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Year 7 Topic 2a: Speed and Forces (Physics)

Contents Contents........................................................................................................................................................... 2

Prior knowledge........................................................................................................................................3Speed............................................................................................................................................................... 4

Distance and displacement.......................................................................................................................... 5Velocity and speed....................................................................................................................................... 6Average and instantaneous velocity and speed...........................................................................................7Investigating velocity....................................................................................................................................7How we gain agreement that an idea is correct in science........................................................................10Distance-time graphs: Sectioning...............................................................................................................10Distance-time graphs: Slope.......................................................................................................................12Distance-time graphs: rates........................................................................................................................14

Acceleration................................................................................................................................................... 16Forces.............................................................................................................................................................17

About forces............................................................................................................................................... 17Drawing forces........................................................................................................................................... 18Non-contact forces.....................................................................................................................................18

Magnetic force........................................................................................................................................19Electrostatic force...................................................................................................................................21Gravitational force – Weight...................................................................................................................22

Contact forces............................................................................................................................................ 23Normal contact force..............................................................................................................................24Upthrust..................................................................................................................................................24Lift........................................................................................................................................................... 27Thrust......................................................................................................................................................28Friction....................................................................................................................................................28Air resistance.......................................................................................................................................... 32Tension................................................................................................................................................... 35

Balancing forces and the resultant force....................................................................................................36Newtons 1st Law of Motion.....................................................................................................................38Unbalanced forces..................................................................................................................................39Balanced forces.......................................................................................................................................39Stretching and squashing........................................................................................................................41Stopping distance................................................................................................................................... 44

Turning effect of forces.............................................................................................................................. 45Force pairs: Newtons 3rd Law......................................................................................................................46

Knowledge Organiser Questions....................................................................................................................47

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Prior knowledge 1. What are the usual units of speed we use in Physics?

a) mph b) m/s c) s/m d) miles per hour

e) N

2. What is the usual unit of distance we use in Physics?a) metre b) kilometre c) mile d) millimetre e) light year

3. What do we call speed in a named direction?a) Scalar b) Energy c) Acceleratio

nd) Force e) Velocity

4. What does the gradient of a graph refer to it?a) Area b) Number of

pointsc) Steepnes

sd) Height e) Intervals

5. Which is the equation we use to calculate speed?a) distance x

timeb) distance ÷

timec) speed = distance x

timed) speed = distance ÷

time6. What do we call any change in velocity?

a) Force a) Energy b) Work Done c) Speed d) Acceleration

7. What is the difference between speed and velocity?a) Direction b) Distance c) Acceleratio

nd) Force e) Energy

8. What are the units of acceleration?a) M b) m c) s d) m/s e) m/s2

9. What are the units of force?a) n b) N c) j d) J e) m/s

10. Which one box best describes what un balanced forces on an object can do?a) Change

speedb) Change

directionc) Change

shaped) Change speed,

direction or shape

e) Not change anything

11. Which one box best describes what balanced forces on an object can do?a) Change

speedb) Change

directionc) Change

shaped) Change speed,

direction or shape

e) Not change anything

12. Which of these is a non-contact force?a) Friction b) Tension c) Upthrust d) Weight e) Thrust

13. Which diagram shows balanced forces

a) b) c) d) e)

14. What must be true for the motion of this tractor? a) Changing

how it moves

b) Moving forwards

c) Starting to move

d) Speeding up

e) Slowing down

15. What do we call the single force that we can use to replace lots of forces in a diagram?

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f) Velocity g) Weight h) Summary i) Resultant j) TotalReflectionBefore the topic End of the topic Score: /

15What were you pleased with? What were you pleased with?

Speed Speed is a measure of how fast something or somebody is moving. It gives us information about how much distance is covered each unit of time. There are many units of speed such as: miles per hour (mph) – an old imperial measurement only. Still

used in vehicles. metres per second (m/s) – these are the ones we usually use in

Science kilometres per hour (km/h) centimetres per year (cm/y)They always have a unit we measure distance in, then the word per, followed by a unit we use to measure time.We use the symbol ‘/’ to represent the word ‘per’. When a physicist reads ‘m/s’ they actually hear ‘metres per second’ in their head. An easier way to read it may be to think of ‘per’ as ‘each’. So 300km/h becomes 300 km each hour.The equation we use to calculate speed must have distance and time. The units of speed depend on the units used for distance and time.

speed = distance ÷ timeRemember: when we do calculations in our exercise book, we:1) Write the general formula out first at the top for each calculation2) line the = signs up one below each other3) Never have more than one = on each line4) Check units

16. This student has the correct answer but would only score 1 out of 4 marks. What have they done poorly in their calculation? Write it correctly scoring all 4 marks.

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17. How far does each thing below travel in the time given?Speed (m/s) Time (s) Distance travelled

a) Person walking 1.5 2b) Person running 3 3c) Person cycling 6 3d) Car 30 mph 13 2e) Car 60mph 30 2f) Sound wave 330 3g) Light wave 300 000 000 3

18. Calculate the speed of each of these animals and add appropriate units

Distance travelled

Time Speed

a) A fly 100 m 10 s b) Cheetah

running45 m 1.5 s

c) Ostrich walking 45 m 15 sd) Peregrine

falcon180m 2

e) Dolphin 2200 m 200 sf) Human jogging 5 km 60 ming) Continent

moving3cm 365 days

19. Light and electromagnetic waves are the fastest things possible. What does 300 000 km/s mean?

20. What are the most common units for speed we use in Science?

Distance and displacement Distance gives us no information about the direction something moves. Values which do not tell us the direction are called scalars. Distance is a scalar.e.g. if I move a distance of 10m I could end up anywhere within a 10m radius of the start point depending on the path I take. This diagram shows three different journeys from A each the same distance but each with very different end points.

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Calculate the speed of a cow if it walks 300m in 1 minute.distance ÷ time = 300 ÷ 1 = 300 ÷ 60 = 5

Displacement is distance in a certain direction from the origin. A value in a certain direction is called a vector. Displacement is a vector. E.g. If I travel 10m upwards from here, there is only one position I could end up. Looking at the diagram above, The middle path has a total displacement of 0m as it ends back

at the start point. The path on the right has a displacement of 10m in the direction

of C. The path on the left has a displacement of around 3m in the

direction B. Remember that each path has a distance of 10m.

21. Use the graphic organiser below to compare distance and displacement.

22. What do both scalars and vectors have in common?23. How would you convert any scalar value into a vector?24. A teacher goes for a walk in a lesson and writes this true note: “I walked a total

distance of 50m but my total displacement was only 1m forwards.” Explain what has happened?

Velocity and speed Speed and velocity are often interchanged. They have the same relationship to each other as distance and displacement. Velocity is a speed in a direction.A value of speed for an object tells us nothing about its direction. Remember that values that only tell us how big something is are called scalars. Speed is a scalar e.g. 10m/s is a scalar as it does not tell us which way the object is moving.If we add information about the direction a scalar is pointing it becomes a vector. Velocity is the vector version of speed. 10m/s East is a velocity as it has size and direction. Velocity is a vector.

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25. A boat is travelling at 45 km/h. Why is this value a speed and not a velocity?26. Identify if each of these values is a speed, a velocity, a distance or a

displacement.a) 30 m/s b) 30m c) 30 m/s downd) 45 m/s e) 45 m/s f) 45 m g) 67 km/s East h) 67 cm/hr toward

Londoni) 30m left

j) 45m starting here k) 45 mm l) 45 nm down27. Use the graphic organiser below to compare speed and velocity.

28. The Moon travels around the Earth once every 28 days. It has a constant speed but its velocity is changing constantly. Explain how this is possible.

29. Extended writing challenge. You score points by using key words. You can use words more than once.Billy gets onto a big wheel and goes around once (a total of 30m) in one minute.When he gets off he tells Tara that his displacement was zero. The owner reminds him that he travelled all the way around the wheel (30m).Explain how both Billy and Tara are correct.

1 Point: Velocity Speed

2 Points: Direction Vector

3 Points: Total displacement Scalar

Average and instantaneous velocity and speed If we were running a race, our speed would change as we ran. At the start it would be zero then it would increase as we got into the swing. It may start decreasing as we get tired towards the end. In this case, we could use the term velocity instead of speed as we know that we are running from the start of the race to the end in a known direction.The instantaneous speed is the speed at one instant of time. The average speed would be a single value which would cover the entire distance and the entire time taken. The average speed is a simplification we often use.

30. What is the difference between instantaneous speed and average speed?

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31. Calculate the instantaneous velocity of this runner at each stage in the race.Part of race Distance covered

(m)Time taken (s) Speed (m/s)

Start 0 1First stage 20 4Middle stage 50 5Final stage 30 4

32. Calculate the average velocity of this runner over the entire race.33. What is the difference between speed and velocity?34. What is the difference between displacement and distance?35. What is the equation for speed?36. What are the normal units we use for speed?Investigating velocity

Use the following structure strip to plan your investigation.37. Hypothesis

being tested? (simple statement stating a relationship)

The speed of a marble is affected by the surface it is rolling on.

38. Independent variable (you change)

39. Dependent variable (you will measure )

40. 3 control 1)8

variables (ensures only the IV affects the DV – makes it fair)Do not pick same measuring device (ruler)

2)

3)

46. Step by step method (start each line with a command verb e.g. measure, set-up, record)

1)

2)

3)

4)

5)

6)

58. Risk assessment(3 most obvious hazards in your experiment and how you will reduce their risk)

1)

2)

3)

Now test your hypothesis using the method. Write your results in the table below.Surfaces tested

Distance marble travels in 2 seconds (cm) Average speed of marble (cm/s)

1st test 2nd test 3rd test Average distance

Normal floor

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64. Are there any anomalous results (ones that do not fit the pattern)? How can you tell? If you have some put a circle around them. We will ignore these results from now on. Pretend they don’t exist.

65. What sort of errors cause anomalous results? Tick the correct boxa) Random errors – ones we cannot predict Systematic errors – ones we can

predict66. What should we do with anomalous results?67. Calculate the mean average value for Average speed of marble for each surface.

Using mean = (1st test + 2nd test + 3rd test) ÷ 3 Remember to ignore anomalies e.g. If 2nd test result is anomalous then mean = (1st

test + 3rd test) ÷ 268. Plot a bar chart of Average speed of marble vs Distance the block is pushed

(cm) It should look something like this when complete

69. Write your conclusion for your chart using this prompt:As we change the surface the speed of the marble { Changes

Doesn' t change}. 70. What do you notice about surfaces that seem to slow the marble down more?71. Does your investigation support your hypothesis? How can you tell?72. Look at the KO Questions. Practice Look, Read, Cover, Write, Check for 5

minutes. Then work with your partner and test each other for another 5 minutes. Write a list of the 5Q numbers you are most confident with. Write another list with the 5Q you are least confident with.

How we gain agreement that an idea is correct in science We share our results and methods so that other people can check our claims and ensure they are valid. We call this process peer review. There are three main things we look for to gain confidence that something is correct:1. How reliable is the source? Some are bias or

misleading.

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2. Has the person repeated and got same results? If so, the results are called repeatable.

3. Have different people get similar results using different methods? If so, we call the results reproducible.

Results that have not passed these three checks may be incorrect.

73. What could you do now to increase your confidence that everyone agrees with your answer? What would you hope to find discover?

74. If other people in your class got the same results as you using a different technique (e.g. different slope) would that make your results repeatable or reproducible? Say why?

Distance-time graphs: Sectioning In science we often use graphs to help us understand numbers more easily. They allow us to spot patterns.Distance-time are some of the only line graphs where we use dot-to-dot.

When we interpret graphs there are three rules we always follow:1. Always start at the origin (this means beginning)2. Use a ruler to split the graph into different sections. A

section can be spotted as the line seems to do the same thing in it. In this graph of Sam’s journey to school there are three different sections time: 0 to 5 minutes; 5 to 15 minutes and 15 to 20 minutes.

3. Consider each section separately. For time 0 to 5 minutes: distance travelled = 0.6km. Time taken

= 5minSpeed = distance ÷ time = 0.6 ÷ 5 = 0.12 km / min

For time 5 to 15 minutes: distance travelled = 0km. Time taken = 10min

For time 15 to 20 minutes: distance travelled = 0.6km. Time taken = 5min

75. Section the graph above using a ruler.

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76. Calculate the speed for next two sections of Sam’s journey to school. Lay them out in same way as shown in the example.

77. Calculate the average speed for Sam over his entire journey to school.78. Explain how to read scales using bar models to help.79. Where is the origin of a graph? What does origin mean?80. Section the graph below and calculate the speed for each section separately.

81. Calculate the average speed for the graph above.

82. Complete MultiChoice Questions Topic 7.1a. List 5Qs you are happy with and 5Qs you are not.

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83. Section the graph below and calculate the speed for each section separately.

84. Calculate the average speed for the graph above.

Distance-time graphs: Slope Our brains are far quicker at spotting patterns in pictures. That’s’ why we use graphs.Graphs can be especially useful for spotting mistakes as they do not fit the pattern. We call results that do not fit the pattern anomalous and we ignore them from our analysis. Anomalies are caused by random errors such as human error.On any graph there are three things we can use to spot patterns: The height of each point compared to other points The steepness/slope of the line. We call this gradient or rate of

change The area under a lineFor distance-time graphs, the gradient and how it changes tells us about the speed. Straight lines tell us that things are constant. Curves tells us that things are changing.

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85. Why do we use graphs to present our results rather than tables?86. How can we spot anomalous results on a graph? What should we do with them?87. The graph below has been put into sections already for you. Match each section

to the correct description opposite. Be careful there is one description that does not fit.

88. What is the total displacement in this journey?89. Calculate speed for each section of the journey shown in the graph above.90. Using the blank grid, sketch the journey described in the table below.

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Stationary

Speeding up – accelerating

Low constant speed forwards

Medium constant speed backwards

Fastest constant speed forwards

91. By looking at the slopes, can you rank each section of the graph above into order of speed slowest to fastest.

92. Calculate speed for each section of the journey shown in the graph above.

Distance-time graphs: rates We use graphs across all of science and the idea of gradients (steepness) is important for all. A more useful way may be to call the gradient (steepness) the rate of change. This means we can use the same language for any graph regardless of what information it is showing us.

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Section of journey

A. Journey starts at 0m distance

B. For time 0-40s: constant speed until distance = 4m

C. For time 40-60s: constant speed until distance = 7m

D. For time 60-70s: stationary

E. For time 70-90s: constant speed until distance = 4m

F. For time 90-120s: constant speed until distance = 0m

93. What is the difference between a vector and a scalar?94. What does the steepness of a line on a distance-time graph tell you about

speed?95. How is it possible to walk 100m but end up with a displacement of 0m from

where you started?96. A train travels at 40km/hr how many km does it travel each hour? How many

will it travel in 3hrs?97. How can you tell if a result on a graph is anomalous? 98. What is the difference between instantaneous velocity and average velocity?99. Extended writing challenge. You score points by using key words. You can use

words more than once.Sometimes we use sketch graphs to describe patterns in less detail.Drew thought about his different speeds over his science lesson and sketched this graph. Describe the 4 different sections of this graph and predict what was happening at each.

1 Point: Speed Stationary

2 Points: Constant Sitting down Increased

breathing rate3 Points:

Walking to class Velocity Increased

respiration

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100. Section this graph into its 4 different parts. Use the conclusions from below to describe each section.

101. Calculate the speeds of each of the straight-line sections.102. For the curved section, state the initial speed, the final speed and how long it

took.103. How would the curved sections change if the object had accelerated at a higher

rate?104. Look at the KO Questions. Practice Look, Read, Cover, Write, Check for 5

minutes. Then work with your partner and test each other for another 5 minutes. Write a list of the 5Q numbers you are most confident with. Write another list with the 5Q you are least confident with.

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Acceleration There are big misconceptions with the term acceleration. This is because it is described differently in science and everyday life. We need to be careful when using.When an object accelerates its velocity must change. These situations are all accelerations: Increase in speed – the most common everyday use of the word Decrease in speed – sometimes called deceleration or negative

acceleration Change in direction – we must not forget this oneThe other thing to be careful of is using the word speed in the same sentence as acceleration. E.g. “An object accelerates at a constant speed” makes no sense.The units of acceleration can be confusing. They are written m/s/s or m/s2.When things fall on Earth they accelerate at 9.8 m/s/s. This means that they change speed by 9.8 metres each second, each second. If we drop something off a table, it’s instantaneous speed at the start is 0m/s. An acceleration of 9.8m/s tells us that each second this speed will increase by 9.8m/s.A single force will cause accelerations. We will look at this later in this topic.

105. Which of these situations shows acceleration? Tick the ones that do. A rocket landing on

the moon A car going around a

corner A ball slowing down

as it hits the floor An asteroid heading

through space at constant velocity

A cricket player hitting a ball

The Earth travelling at a constant speed around the Sun

An aeroplane taking off

A helicopter hovering A book on a table

A pen falling off a table

A pen falling off a table on the Moon

A pen falling off a table in Space

106. Gravity is much weaker in space than on Earth. If a ball in space accelerates at only 2 m/s/s how long will it take to reach 10 m/s if it started at 0 m/s?

107. What is the problem with this answer:

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108. What are the units of acceleration? Write down how you would say them out loud.

Forces About forces

A single force will cause motion to change (direction or speed). If there is more than one force then they may also cause objects to change shape.

Sir Isaac Newton is considered to be one of the most influential scientists ever. His work on forces (Naturalis Principia Mathematica, 1687) still provides the basis of much of our understanding of why the Universe behaves the way it does. As well as the three Laws of Motion which bear Newton’s name the unit of force is known as the Newton (N).Forces are pushes or pulls experienced by an object. Some require contact but some can act at a distance with no contact.

These non-contact forces were considered the strangest and their nature is still being discussed today. Even in 1915, Einstein was looking into gravitational forces in his theory of General Relativity. When we measure forces, we use a forcemeter. This is a

simple device that is calibrated for use on Earth. This means it has been set to

only work on Earth with Earths gravitational field. It could not be used on

another planet or in space.There are some forces we need to know the name of:Contact forces: Non-contact forces: Normal contact force Magnetic force Friction Electrostatic forces Thrust Gravitational force -

Weight Tension

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When a car starts a journey from stationary it accelerates. This means that the speed increases. As the driver pushes their foot on the accelerator pedal harder acceleration increases at an increasing speed.When the driver uses the brakes, the car uses negative acceleration at a lower speed until it stops.

Air resistance109. What device do we use to measure force?110. What are the two groups of forces?111. What is the unit we use to measure force? Who is it named after?112. How can a single force affect an objects motion?

113. Look at the KO Questions. Practice Look, Read, Cover, Write, Check for 5 minutes. Then work with your partner and test each other for another 5 minutes. Write a list of the 5Q numbers you are most confident with. Write another list with the 5Q you are least confident with.

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Drawing forces Forces are vectors. This means they have size and direction.When we draw forces, we use arrows to indicate the direction. To show the size of the forces, we either write the size next to them or change the size of the arrow. We often use a circle to represent the object instead of trying to draw it out again.Both of these force diagrams represent the samesituation.

114. Use this graphic organiser to compare the two methods for drawing forces.

115. What does the size of a force arrow tell you?

Non-contact forces Non-contact forces do not need to touch an object in order to exert a force on it. They have force fields around them that we cannot see but can observe through some practicals. These fields have field lines that cannot cross each other.The closer the field lines are together, the stronger the force experienced.

116. Name the three non-contact forces117. How can you use the field lines to see where a force is strongest?

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118. What rule must you remember when drawing field lines?

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Magnetic force A magnetic force is experienced by any magnetic material in a magnetic field. Every magnet has a South and a North pole. It is impossible to have one on its own.There are only 4 magnetic materials: Iron Steel Cobalt NickelOpposite magnetic poles (N - S or S - N) attract each other.

Similar magnetic poles (S-S or N-N) repel each other

Magnetic field lines:

119. Which substances are magnetic? Tick the correct boxes. Metal Iron Copper Plastic Wood Graphite Carbon Cobalt Electrons Nickel Iron oxide Steel

120. On the magnetic field lines above, label where the field is strongest.Magnetics investigationYou will be given four identical boxes. Inside each box is a material: a magnet; some iron; and some copper. Without opening or shaking the boxes can you determine what is in each box.Record your predictions and results into this table.

Box Number Prediction ahead of test Hypothesis after testing123

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Use the structure strip below to write a method for this investigation and how it helped you decide.121. Step by

step method (start each line with a command verb e.g. measure, set-up, record)

1)

2)

3)

4)

5)

6)

133. Risk assessment(3 most obvious hazards in your experiment

1)

2)

3)24

and how you will reduce their risk)

Electrostatic force An electrostatic force is experienced by any charged particle in an electric field. It is the reason that negative electrons are attracted to the positive nucleus of an atom. It is also the force that causes chemical reactions and holds molecules together.Unlike magnets, it is possible to separate + and – charges.Opposite charges (+ and -) attract:

Like charges (- and -, or + and +) repel:

Electrostatic field lines

139. On the electrostatic field lines above, label where the field is weakest.140. Use this graphic organiser to compare the two non-contact forces.

Experiencing the electrostatic forceWe actually experience it all the time. It is the force that stops the atoms in our bodies passing through the empty space around other atoms. It is also the force that causes all chemical reactions. Here are three demonstrations to experience electrostatic forces.

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Van der Graaf ‘lightening’ sparks.Each spark is full of electrons repelling each other.

Rub a balloon on your hair. It gains charge and will attract to walls via electrostatic force.

Rub a plastic rod with cloth. It gains charge. It will bend a stream of water without touching

Gravitational force – Weight A gravitational force (weight) is experienced by any mass in a gravitational field (gravity). It is an attractive force only. It cannot repel.All objects in the Universe experience the effects of gravity and so have a weight. When we say we feel weightless, that does not mean we have no weight only that we cannot feel it because nothing is stopping us falling.All masses are attracted towards each other by gravitational force. The bigger the masses, the bigger the attraction.Misconception 1: Some people wrongly think, that weight and mass are not the same thing. Weight is a force that acts on a mass because of gravity. It is measured in Newtons (N). Your weight depends upon the planet you are on. Mass is a measure of the matter (particles) in something. It is measured in kilograms (kg). It does not depend upon the planet you are on.They are related to each other using the equation Weight = mass x gravity.Misconception 2: People often get weight and gravity confused. Weight and gravity are not the same thing.Weight is a force which is caused by gravity. Weight = mass x gravityGravity is the strength of the gravitational field in a location. It is sometimes called g. On Earth gravity, g, is 9.8N/kg.Misconception 3: Often people incorrectly imagine that weight only acts downward. Firstly, Earth is spherical so weight on Earth acts towards the centre of Earth rather than down. Secondly, even in space objects have weight and are attracted to other objects with mass such as the Sun or Moon.Gravitational field around Earth

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141. Is there gravity in space? Why do you say this?142. Use this table to calculate the weight of objects in different places in the

Universe.Object Mass of

object (kg)

Weight of object in Newtons if it was on…Earthg = 9.8 N/kg

The Moong = 1.6 N/kg

Jupiter surfaceg = 25 N/kg

Surface of Sung = 274 N/kg

Persons head

5 W = m x gW = 5 x 9.8W = 49 N

a) b) c)

Pushbike 15 d) e) f) g)London bus 10000 h) i) j) k)Wellington 0.05 l) m) n) o)

143. When we feel weightless on a fairground ride, are really weightless? Why do we feel that way?

144. Use this graphic organiser to compare the weight and mass.

145. What is the equation we use to calculate weight?146. What is wrong with this student answer?

Contact forces Until you study A-level Physics, any forces that are not magnetic, electrostatic or gravitational force are considered contact forces. These are forces that act between objects that are physically touching each other. Be careful to remember that hitting particles in a gas or liquid is still considered contact.

147. What are the 3 non-contact forces?148. What are the normal units we use for speed and velocity?149. What are the normal units we use for acceleration?

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Objects with lots of particles in have a bigger weight in kg than ones with less. If we took them into space they would have a mass of 0N as there is no gravity or particles in space (it is a vacuum).

150. What are the units of force?151. Does hitting any type of particle count as a contact force? Why do you say this?152. Silent Debate. You will work in a group of 3 or 4 people. Each needs a different

coloured pen.Rules: #1 You must write on each other’s sheets #2 Write in clear English no text-speak or abbreviations. #3 Stay on topic. #4 You must be silent. You can only write your argument points down on this paper. #5 Use arrows to challenge specific points and write next to them.

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Question to discuss: Imagine we want to break a speed record. Use your knowledge of contact and non-contact forces and the particle model to predict which speed record is easiest to break and why? Current records are: Underwater ~100km/h. On the water ~ 500km/h. In the air ~ 850km/h. In space~ 39500km/h.

Normal contact force When an object pushes against a solid surface it experiences a normal contact force. This force always acts at a right angle to the surface being touched.

153. Draw the normal contact force for each of these situations

a) b) c)d)

e) f)g) h)

154. What state of matter is associated with normal contact forces?155. What are the units for force? Who are they named after?Upthrust

When an object is placed in a liquid or gas it pushes particles out of the way. These particles push back and this results in upthrust. The size of the upthrust force is equal to the weight of liquid or gas moved out of the way (displaced) by the object. If the upthrust on an object is the same as its weight then it will float.

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156. What state of matter is associated with normal contact forces?157. Name the forces on these diagrams

a) b) c) d)

e) f) g) h)Investigating upthrust

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Object Weight in Air (N) Apparent weight in water (N)

Upthrust force from water (N)

Wood block

Aluminium block

Polystyrene block

Iron block

158. What size must the upthrust be to make an object float if the object has a weight of 1000N?

159. What is wrong with this diagram of the particles in a liquid?

160. Draw the particle diagrams for a solid, a liquid and a gas. Include 9 particles. Check they are all the same size.

Solid Liquid Gas161. Which particles are closest? What does this mean in terms of density?162. If you threw a solid, liquid and a gas into some water, which is most likely to

float up to the top? Which is most likely to sink?163. Complete these sentences:

Substances sink because they have a ___________ density than the fluid (liquid or gas) they are in. This is why _____________ normally sink in water.Substances float because they have a ___________ density than the fluid (liquid or gas) they are in. This is why _____________ normally rise upwards in water.

164. Both diagrams below show the same substance in solid state but at different temperatures.

a) Which is the hottest?b) Which is most dense? c) Which is most likely to float in water? d) Which would have the greatest upthrust?

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Lift This is really a push force generated by a specific flow of gas or liquid particles over a wing surface. It only exists if particles are flowing over the wing and disappears when they stop. It is often confused with up-thrust.

165. If the plane above stopped moving forwards, what would happen to the lift?166. What mixture of gases is the wing running into as it flies?Investigating Lift

167. In both experiments you generate lift. What happens in both experiments when you stop blowing?

168. Use the visual planner to compare lift and upthrust

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Thrust A general term for any push on an object caused by an engine or a deliberate shove.

169. Name 3 different types of vehicle that use the thrust of an engine to move.170. If this car was going backwards which direction would the thrust force be acting?171. Name the 3 non-contact forces.172. Where in a magnetic field is the magnetic force strongest?173. What are the four magnetic metals?Friction

Two objects sliding past each other experience friction forces. For example, a box sliding down a slope. Friction always tries to stop movement. The faster something moves; the greater friction is.This is caused by tiny ridges on each object scratching past each other. The smoother the surfaces the lower the friction. Think about ice or oil on the road.Energy is transferred from the kinetic store to the thermal store during friction. This is why things get hot. You will learn about this more in Year 8.

174. What causes friction?175. Why has ice far less friction force that concrete?176. Why does wearing spikes or studs on shoes increase the friction force?

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177. Use the diagram below to explain why adding a layer of oil (lubricant) between the two surfaces reduces friction?

Without lubricant With lubricant178. Use the diagram to explain why heavier object experience more friction?

Low weight High weight

Investigating friction and mass


being tested? (simple statement

The mass of a shoe affects its friction force

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stating a relationship)


181. Dependent variable (you will measure)

182. 3 control variables (ensures only the IV affects the DV – makes it fair)Do not pick same measuring device (ruler)

1)

2)

3)


1)

2)

3)

4)

5)

6)


1)

2)

3)

Now test your hypothesis using the method. Write your results in the table below.Mass in Force required to pull shoe (N)

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shoe (g) 1st test 2nd test 3rd test Average0

200

400

600

800

1000

206. Are there any anomalous results (ones that do not fit the pattern)? How can you tell? If you have some put a circle around them. We will ignore these results from now on. Pretend they don’t exist.


predict208. What should we do with anomalous results?209. Calculate the mean average value for Force Required to Pull Shoe for each Mass

in Shoe.Using mean = (1st test + 2nd test + 3rd test) ÷ 3 Remember to ignore anomalies e.g. If 2nd test result is anomalous then mean = (1st

test + 3rd test) ÷ 2210. Plot a graph of Mass in Shoe (g) vs Average Force Required to pull shoe (N).

It should look something like this when complete

211. Draw your line or curve of best fit. Remember it doesn’t have to touch any of the points at all or even go through the origin.

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213. Write your conclusion for your graph using this prompt:

As ‘mass in shoe’ increases, the ’force required to pull shoe’ { increasesdecreases

stays the same}. The steepness of the graph { increases

decreasesstays the same} so the rate of change also { increases

decreasesstays the same} .

214. Predict how much force would be needed to pull a shoe with 1200g mass in it. Describe how you came up with this prediction.

215. Does your investigation support your hypothesis? Why do you think that?216. What could you do now to increase your confidence that everyone agrees with

your answer? What would you hope to find discover?217. If other people in your class got the same results as you using a different

technique (e.g. different ball) would that make your results repeatable or reproducible? Say why?

218. Why might we be suspicious of the results from a climbing shoe manufacturer?Air resistance

Sometimes called drag. Air resistance always tries to stop movement. The faster something moves; the greater air resistance is.An object moving through the air experiences air resistance. For example, a skydiver falling through the air.This is caused by the object hitting air particles as it moves. The faster it goes, the harder it hits. Think about when you put your hand out of a moving car window.

219. What happens to air resistance as an object falls through it faster? Why is this?220. Looking at the pictures below, why does the car experience less air resistance

that the lorry when it moves at the same speed?

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221. Add the following force arrows and labels to the two vehicles above. Assume they are all travelling at a constant speed. Tick each force when you’ve added it. weigh

t frictio

n air

resistance normal contact

force thrust of engine.

Investigating air resistance


being tested? (simple statement stating a relationship)

The shape of the paper affects its speed as it falls




1)

2)

3)


1)

2)

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3)

4)

5)

6)


1)

2)

3)

Now test your hypothesis using the method. Write your results in the table below.Shape of

paperTime to fall 2m (s) Average

speed (m/s)1st test 2nd test 3rd test AverageFlat

Scrunched249. Are there any anomalous results (ones that do not fit the pattern)? How can you

tell? If you have some put a circle around them. We will ignore these results from now on. Pretend they don’t exist.


predict251. What should we do with anomalous results?252. Calculate the mean average value for Time to fall 2m for each shape of paper.

Using mean = (1st test + 2nd test + 3rd test) ÷ 3 Remember to ignore anomalies e.g. If 2nd test result is anomalous then mean = (1st test + 3rd test) ÷ 2

253. Now calculate the average speed for each shape. Use the distance of 2m and your average time to fall in seconds.

In the late 16th Century, Galileo Galilei became interested in the effects of air resistance on objects and came up with the revolutionary idea that all objects fall with the same acceleration.

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To test this hypothesis, he dropped two identically shaped but different mass balls from the top of the Leaning Tower of Pisa. Everyone thought that the heavy ball would fall faster, but it didn’t. Both hit the ground at the same time. They accelerated at 9.8m/s/s (g on Earth). As a consequence, the old model for gravity was replaced with a new one. It was famously repeated during the first Moon landing with a hammer and feather.

You can recreate his experiment by dropping two identical bottles of water, one full and one empty, at the same time. Or you can watch this excellent video exploring the effect of air resistance: https://youtu.be/74MUjUj7bp8

Tension An object that is pulling is exerting a tension force. For example, a cable feels a tension force when it is holding a ceiling lamp.

In normal life, tension tends to be used to indicate someone feeling anxious or under strain. Interestingly, the terms strain, stress and pressure are all used in describing forces. Jolt and jerk are also force related words that seem to have crept into our normal-life vocabulary.

254. Compare tension force and thrust force using the visual organiser below.

255. Lots of forces have two names. Draw lines to connect the terms that mean the same thing.

Tension Push Weight

Pull Gravitational force

Air resistance

Drag Upthrust Thrust

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https://youtu.be/74MUjUj7bp8

Buoyancy Amount of matter

Mass

256. Why is air resistance a contact force?257. Name the 3 non-contact forces.258. Name the 4 magnetic metals.

259. Complete MultiChoice Questions Topic 7.1b. List 5Qs you are happy with and 5Qs you are not.

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Balancing forces and the resultant force We consider all the forces acting on an object to determine what happens to its motion (speed or direction) or shape.The resultant force is a single force which summarises all the others in one go. It is sometimes easier to think of it as a result between two or more teams of forces. The winning force tells us the direction of the resultant, the amount they win by tells us the size of the resultant.If all the forces cancel each other out, we say they are balanced. In this case the resultant (the result of all the forces) would be zero.

If they do not cancel each other out we say the forces are unbalanced. In this case the resultant (the result of all the forces) would not be zero.

260. For each of these force diagrams say if the forces are balanced or unbalanced. If they are unbalanced, which direction wins and estimate the resultant.

a) b) c)

d) e) f)

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g) h) i)261. Match the correct resultant to the force diagram

Unbalanced forces

Resultant is… …3 N

Unbalanced forces

Resultant is……6 N upwards

Unbalanced forces

Resultant is… …6 N downwards

Balanced forcesResultant is…

…0 N

262. Draw the normal contact forces and weight force for these objects.

a)

b)

c)

263. For each of the three diagrams above, are the forces balanced or unbalanced? Can you estimate the direction of the resultant force?

264. What are the units of force?

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Newtons 1 st Law of Motion “An objects motion will not change unless acted on by an external resultant force.”This means that if the resultant force is zero and the forces are balanced, then an object will keep doing whatever it is doing. It cannot change speed or direction.This means that if the resultant force is not zero and the forces are unbalanced, then an object will change speed, direction or both.

266. An object is moving at 3m/s and the forces on it are balanced. What will its motion be like 1second in the future? Will it have moved? Will it have changed speed? Will it have changed direction?

267. An object changes direction but keeps moving at the same speed. Are the forces on it balanced or unbalanced? Why do you say this?

268. If an object is not moving, are the forces on it balanced or unbalanced? Why do you say this?

269. What is the difference between speed and velocity?270. A rocket going to the Moon experiences no air-resistance because space is a

vacuum. It switches its engines off and all forces on it are now balanced. What will happen to its velocity?

271. Some textbooks say that when forces are balanced an object will either continue moving at a constant speed in the same direction or it will remain stationary. Explain why this fits Newton’s 1st Law?

272. A car is travelling at its top speed in a constant direction. Its velocitydoes not change. For this to happen, its engine gives a thrust force. Are the forces on this car balanced? Why do you say this?

273. If the forces on an object are balanced, what is the resultant force on that object?

274. Label the forces on this diagram of a diamond falling through water at constant speed.

275. Correct each paragraph in this student statement

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276. On Earth an object falling through air eventually reaches a top speed (called terminal velocity). What two forces must be balanced at this point for this to happen?

Unbalanced forces When forces are unbalanced it causes change. The resultant force will not equal zero. This means one of more of these things will happen Change in speed Change in direction Change in shapeAny change in any of these three areas show us that the forces on that object must be unbalanced and that there must be a resultant force.Misconception: Some people forget that changing direction is also acceleration. E.g. An object travelling around a circle at a constant speed is changing direction and so is accelerating. This means it must be experiencing unbalanced forces and a resultant force (in this case towards the centre of the circle).

277. What are the three things an object can do if the forces on it are unbalanced?278. Why are objects travelling around corners always considered to be accelerating?279. The resultant force a car is 0 N and it is currently travelling backwards at 30m/s.

How will its motion change in the future?280. A person standing on a table pushes down a Weight of 800N. The table pushes

back with a normal contact force of 700N. What is going to happen to the motion of the person?

Balanced forces Balanced forces do not cause motion to change. If an object is already moving, it will continue to do so in the same way. No force

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When I start pedalling my bike the forces are balanced because I do not fall over.As my speed increases the forces cannot be balanced. The push from my legs is greater than weight and air resistance.The faster I go the less air particles I hit so the air resistance decreases. I know this because my hair gets pushed backwards by the wind it causes.Eventually I reach a top speed and I can’t go any faster. This is because my push, friction and air resistance have all disappeared.

} both cause a change in velocity which we call acceleration

‘wins’ when the situation is balanced. Therefore, the result must be a draw and the resultant must be zero.If speed, direction or shape of an object is changing then the forces cannot be balanced.Misconception: Many people think that moving means accelerating but it does not. E.g. An aeroplane flying upward at a constant velocity is not changing its direction or speed. The forces acting on it must be balanced and the resultant force must be zero.

281. What is the equation for speed?282. Section this graph and look at the axis titles283. On which 5 points on this graph does speed

change? What can you say about the forces on the object at each of these points?

284. How can you tell by looking that the speed is constant for time 20 to 30 seconds?

285. By looking, which section is the object moving fastest?

286. Calculate the speed for each section287. The forces on this paper plan are balanced.

a) Describe the resultant force acting on it?b) What will happen to its motion?

288. For each scenario below state if the forces are balanced, unbalanced or you cannot tell.

a) A ball not moving

b) A bull speeding up

c) An apple falling

d) Book sat on table

e) Bubble rising in water at constant velocity

f) Hot air balloon landing

g) Tennis ball bouncing on floor

h) The Earth going around the Sun

i) Aeroplane rising at constant speed and direction

j) A bee flying up keeping its speed and direction the same

k) A car with its engine revving at traffic lights

l) A spring being stretched at constant speed and direction

m)A skater slowing down

n) Bird flying a loop-the-loop

o) Train going backwards

p) Moon orbiting Earth

289. Use the visual organiser to compare balanced and unbalanced forces and their effects.

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Stretching and squashing If an object changes shape this is evidence of unbalanced forces. If it eventually stops changing then this tells us that the forces have become balanced.Objects that return back to their original shape are called elastic.

Investigating stretching a spring

Use the structure strip below to write a hypothesis and a method to test it.

290. Hypothesis being tested? (simple statement stating a relationship)




1)

2)

3)50


1)

2)

3)

4)

5)

6)


1)

2)

3)

Now test your hypothesis using the method. Write your results in the table below.317. Construct your own table to record your results. Remember that your

independent variable goes on the left-hand side and your dependent variable goes on the right.

Original length of spring (cm)

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318. Are there any anomalous results in your table (ones that do not fit the pattern)? How can you tell? If you have some put a circle around them. We will ignore these results from now on. Pretend they don’t exist.

319. A zero error is one where the measuring device does not start at 0 when there is nothing on it. Does your forcemeter have a zero error? What could you do to fix it if it did?

320. Plot your results on graph paper. Your graph should look something like this.

In this example, there is an anomalous result at 300g. It has been circled it and then ignored from the line of best fit.

321. Are there any anomalous results in your graph (ones that do not fit the pattern)? How can you tell? If you have some put a circle around them. We will ignore these results from now on. Pretend they don’t exist.

322. Look at the origin of your plotted graph. Origin means start point. Starting there and looking right, what happens to the line and its steepness. Use this to write your conclusion for your graph with this prompt:

As ‘mass on spring’ increases the ‘amount the spring is stretched’ { increasesdecreases

stays the same}. The steepness of the graph { increases

decreasesstays the same} so the rate of change also { increases

decreasesstays the same} .

323. If you did this experiment again, what one thing could you do to improve what you did? Why would this improve the experiment?

324. Complete MultiChoice Questions Topic 7.1a. List 5Qs you are happy with and 5Qs you are not.

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Stopping distance When we want to stop quickly we need to reduce our speed. This means we need to accelerate (in this case it will be negative acceleration). For this to happen we need a resultant force provided by whatever we are using to brake. Three main factors affect how quickly we can reduce our speed to stationary (stopped): The speed you are travelling The time it takes to decide to apply the brakes How much braking force we can exertIf we are travelling on a motorcycle at 30m/s (30m each second) which is around 70 miles per hour. Then every second we take before applying the brakes we will move an extra 30m. The distance covered would be less if we were travelling slower. The state of the road and our brakes will affect how much braking force we can apply.We consider two parts of the stopping distance separately: Thinking distance – the distance travelled while we react Braking distance – the distance travelled while the brakes are on

and we are slowing down (accelerating).

325. For each factor say if it would affect your reaction time or your cars braking force?

a) Being tired b) Old age c) Drugs d) Wet roade) Broken brakes f) Heavy car g) Being distracted h) Alcoholi) Poor visibility j) Number of

wheelsk) No grip on tyres l) Ice on road

326. For each factor say if it would affect your thinking distance or your cars braking distance?

a) Being tired b) Old age c) Drugs d) Wet roade) Broken brakes f) Heavy car g) Being distracted h) Alcoholi) Poor visibility j) Number of

wheelsk) No grip on tyres l) Ice on road

327. What is the one factor that affects both thinking distance and braking distance?

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Investigating reaction time

Turning effect of forces If an object can move but is fixed at one point then a force can cause the object to turn around that pivot (or fulcrum) point. We call this the turning effect or the moment of a force. A lever is a simple machine which uses the moment of a force to move objects. Spanners, doors and even our arms are examples of levers.

The size of a turning effect of a force depends upon two factors: The size of the effort force (how hard you push/pull) The distance of the effort force from the pivotThe size of the turning effect of the load depends on the same two factors. When an object balances the clockwise and anticlockwise turning effects must be equal is size. If one direction is bigger than the other then the object will rotate that way.Our body uses muscles to exert forces. Muscle tissue is made of muscle cells. Muscle cells are specialised cells which can pull to do work.

328. Label this muscle cell using the key words and description

Nucleus Where all the chemical reactions happen

Cytoplasm Controls what goes into and out of the cell

Mitochondria Makes new proteinsCell membrane Controls the cell

Ribosomes Performs respiration

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329. Why do muscle cells have so many mitochondria?330. Label on the diagram below the pivot for our elbows.

331. Look at the diagram above. What happens to the length of our bicep when we lift thigs? Why does it do this?

332. Can you name 3 other pivots on our body. What general word do we use to describe the pivots in our skeleton beginning with J?


Force pairs: Newtons 3 rd Law So far we have only considered the forces acting on a single object. This makes it much easier to identify if and how the motion of that object changes. It turns out however that for every force acting on Object A as a result of Object B, there is an identical but opposite force acting backwards Object B caused by Object A.

No force exists by itself.“Every action has an equal and opposite reaction.”If you push on something (action) it pushes back (reaction).

With a racing car the wheel tries to push the road backwards (action) and in return the road pushes the wheel and the car forwards (reaction).Misconception: People often think that because of Newton’s 3rd Law (Every force has an equal and opposite) that all forces must be balanced. This is not the case. Newton’s3rd Law looks at two different objects. When we see if forces are balanced or unbalanced we only consider one object.

334. Complete each of these side-by-side examples on Newton’s 3rd Law force pairs:55

Notes

First force Rocket pushes gas downwards

Cannon pushing ball forwards

c) f)

Type of force Push a) d) g)

Equal and opposite force

Gas pushes rocket upwards

b) e) h)

335. Describe the equal and opposite force for each of these situations:a) Earth’s gravitational pull on the Moon.b) A proton pulled toward an electron by electrostatic force.

336. Complete MultiChoice Questions Topic 7.1b. List 5Qs you are happy with and 5Qs you are not.

Knowledge Organiser Questions KQ.1. What is the equation for speed? Speed = distance ÷ timeKQ.2. What are the units we normally use for speed? m/sKQ.3. What is displacement? Distance in a directionKQ.4. What is a vector A value with directionKQ.5. What is a scalar A value without directionKQ.6. What do you call speed in a direction? VelocityKQ.7. The total distance ÷ total time? Average speedKQ.8. What do we call the speed at one instant of

time?Instantaneous speed?

KQ.9. What do we call the variable we change in an investigation?

Independent variable

KQ.10. What do we call the variable we measure in an investigation?

Dependent variable

KQ.11. What do we call the variables we keep the same to make an investigation a fair test?

Control variables

KQ.12. Why do we share results/use peer review in science?

Confidence (in our results)

KQ.13. What is the slope of a graph called GradientKQ.14. What sort of lines on graphs do we use

the word constant to describe?Straight lines

KQ.15. What two things might change when something accelerates?

Speed or direction

KQ.16. What are the normal units we use for acceleration?

m/s/s or m/s2

KQ.17. What do we call a change in velocity AccelerationKQ.18. What device do we use to measure force? ForcemeterKQ.19. What are the units of force? Newtons (N)KQ.20. What have magnetic, electrostatic and

gravitation forces all got in common?Non-contact (forces)

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KQ.21. In a force field what does it mean if the lines are closer?

Stronger force

KQ.22. What are the four magnetic materials? Iron, Steel, Cobalt and NickelKQ.23. What does repel mean? Push apartKQ.24. What type of electrical charges attract

each other?+ and –

KQ.25. What is another name for the gravitational force?

Weight

KQ.26. What is the equation relating mass, gravity and weight?

Weight = mass x gravity

KQ.27. What angle to the surface does the normal contact force always act?

Right angle

KQ.28. What do we call the upward force that acts on an aeroplane wing

Lift

KQ.29. What do we call the upward force that helps things float?

Upthrust

KQ.30. What do we call the push force from an engine or shove?

Thrust

KQ.31. Which direction do friction and air resistance always act on an object moving forwards?

Backwards

KQ.32. What type of surfaces have low friction? SmoothKQ.33. What happens to air resistance as an

object moves faster?Increases

KQ.34. What do we call results that do not fit the pattern?

Anomalies (Anomalous results)

KQ.35. What sort of errors cause anomalies? Random errorsKQ.36. What do we call the single force we can

use to show the result of lots of forces acting on an object?

Resultant

KQ.37. How big is the resultant if forces are balanced?

0N

KQ.38. What do we call a situation where the forces acting on an object do not cancel each other out?

Balanced forces

KQ.39. What do we call a situation where the forces acting on an object cancel each other out?

Unbalanced forces

KQ.40. If the forces acting on a moving object are balanced, what will happen to its velocity?

No change (in velocity)

KQ.41. If the forces acting on a moving object are unbalanced, what will happen to its velocity?

Velocity will change

KQ.42. What happens to the velocity of an object if the resultant force acting on it is 0N?

No change (in velocity)

KQ.43. What happens to the velocity of an object if the resultant force acting on it is 10N?

Velocity will change

KQ.44. What three things can change when forces are unbalanced?

Speed, direction, shape

KQ.45. What is the science word describing how much something has stretched?

Extension

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KQ.46. The science word for objects that return to their original shape after being stretched or squashed?

Elastic

KQ.47. The name of the error when a device does not start at 0?

Zero error

KQ.48. The factor that affects both thinking and braking distance?

Speed

KQ.49. The name of the distance you travel while thinking about stopping (reacting)?

Thinking distance

KQ.50. According to Newton’s 3rd Law every action has an equal and …

Opposite reaction

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