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Motion, Mass, Force and Work done

Specific Learning Outcomes (SLO's; these incorporate knowledge, scientific and other essential skills and attitudes). At the end of this unit students will be able to:

Read scales on a variety of measuring devices. Recall the S I units for distance, time, velocity, mass, weight, force.

Make measurement of distance and time to calculate average speed using

Use to calculate d, t or v.

Calculate a gradient from a line graph. >Gradient of a distance vs time graph = velocity. >Gradient of a velocity vs time graph = acceleration.

Use a = change in velocity to calculate acceleration.. time

Define a force as a push or a pull. List the types of force that act on contact. List the forces which act at a distance and draw fields surrounding:- the Earth (Gravitational Force Field )- Van de Graaf generator (Electrostatic Force Field)- bar magnet (Magnetic Force Field)

Describe examples of Action Force - Reaction Force pairs. Draw simple Free Body Force Diagrams using arrows to represent force.

Explain that a Net Force causes an acceleration in the direction of the force. Make measurements of force and mass and graph appropriately. Differentiate between mass and weight.

> Mass is the amount of matter in an object (so would be constant on the moon and earth)> Weight is the Force of gravity acting on that mass (so would be less on the moon).

Use Newton’s Law ( F = ma ) to calculate F, m or a. Describe effects & causes of friction and how it can be reduced/enhanced in everyday objects.

Define “Work done” on an object as the transfer of energy to that object (Joules) Use W = Fd to calculate W (Work done) horizontally and vertically. Use the Conservation of Energy Law and Work done to explain simple levers using

F1d1 = F2d2 eg

/tt/file_convert/5f31f70bf3d8c1464f4be894/document.doc

F2 = _______N

d2 = 0.1 m

F1 = 10 N

d1 = 1 mfulcrum

Unit Word List

acceleration F friction Line Of Best Fit ( LOBF )

scale

action force F gravity litre secondsaction/reaction force pairs

F magnetic Magnetic Force Field speed

Ammeter F pull mass stationaryamps F push Measuring Cylinder Stop watchattraction F reaction millilitre straight line average velocity F support minute Symbol for Unitbalanced force F thrust Thermometerbar magnet F weight Motion timechange in velocity field moving object transfer of energy constant velocity Force Net Force transformedcontact force Force meter Newtons unbalanced force created free-body force

diagram Newton’s Law Unit

deceleratesdegrees Celcius friction force opposite Van de Graaf

generator destroyed fulcrumdistance gradient pull velocityElectronic Balance grams push VoltmeterElectrostatic Force Field

Gravitational Force Field

reaction force volts

equal and opposite Gravitational Potential Energy

rearrange volume

equation Joules repulsion weightF air resistance kilograms rise work done F bouyancy kinetic energy RulerF drag lever runF electrostatic line graph S I units


Reading Scales and SI Units

Fill in the gaps in this Table using a pencil.

Scientific Instrument Quantity Measured Unit Measured in ( word )

Symbol for Unit

Measuring CylinderRulerThermometerStop watchElectronic BalanceAmmeterVoltmeterForce meter


Each set of diagrams shows part of the scale of a measuring instrument. Record the reading shown on each instrument with its correct units. Find the corresponding letter in the key list and write it next to the number of the question. Read off the letters, in order and record the answer to the riddle below the Key List.

_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

Why wouldn’t anyone play with the baby vampire ?

0C

ml

N

ml

Plotting a Graph of Distance against (vs) Time

The diagram below shows a bike at 10 second intervals as it rides over a 60 metre course.

1. Complete the data table below recording the distance from the start and the time it took to get to each distance.

Distance from the start ( metres)

0 15 30 45 60

Time ( seconds) 0 10

2. Draw a fully labelled Distance vs Time graph for the data collected above. ( Remember all of the graphing rules)

3. In the graph above how far did the cyclists travel every ten second interval? ____ __

4. In the graph above how far did the cyclists move every second? ____ __

5. What was the average speed of the cyclists in metres per second? ____ __

6. If the cyclists had continued at the same speed for another 20 seconds how far from the

start would they have ended up? ____ + ______ = _______ ___/tt/file_convert/5f31f70bf3d8c1464f4be894/document.doc

A

Start 15 m 30 m 45 m 60 m

Time

Distance vs Time GraphsCalculating the speed by calculating a GRADIENT

1. Work out the gradients ( velocities ) of the following distance vs time graphs.


Time ( s )

AGradient =

=_____ ____

=_____ __/__

BGradient =

=_____ ____

=_____ __/__

Gradient = =

= 0.6 m / s ( metres per second )

= velocity (speed of the object in a particular direction)

The units of the ‘rise’ go on the top.

The units for the ‘run’ go on the bottom

Run from here to here = 14 – 4 = 10 seconds

Rise ( up )

Run ( along )

Rise From here to here = 9 – 3= 6 metres

0

Distance( m )

4 8 12

8

4

6

2

16

1

2 6 10 14

5

3

7

9

Calculation Practice and Graph Interpretation.


4. Answer the following questions using the velocity formula.a) A sprinter runs the last 100 m of a 200 m race in 10 seconds. What is their average

velocity for the last 100 m? v = ________ _______

= _________ ___ /____

b) A car drives 500 m at a velocity of 5 m/s. How many seconds does it take to travel the distance?

____ __c) A plane flies at 40 m/s for 2 minutes. How many seconds are there in 2 minutes?____

How far does the plane travel?

____ __

d

tv

1. Fill in the gaps in the following sentences using a sharp pencil.An object moving has s____________. If the object is moving in a direction we call it a

vel____________. We use v______________ as the scientific name for speed in equations.

The SI unit for distance is m______________. The SI unit for time is s_____________.

Because velocity is calculated by dividing m____________ by s___________., the SI unit for

v_____________ is __________ per s____________ and we abbreviate it ___/ ____.

2. In a graph of distance vs time the g_____________ of the

L______ of B________ F_____ is calculated by G_____________ = . This has a similar structure to the equation v_____________ = .

3. Work out the velocity of the object for each of the sections of the graph opposite.i) From A to B. v =

= _________ m / s

ii) From B to C. v = _________ ______

= _________ ___ /____

iii) From C to D. v = _________ ______

= _________ ___ /____

iv) From D to E. v = _________ ______

= _________ ___ /____

ACROSS5. The SI units for mass9. An unbalanced force acting on an object causes this11. The type of motion caused by balanced forces acting on an object (“stopped” is an

example of this)12. The SI unit that Work is measured in13. Sets of 2 forces that act on an object as an action-reaction (eg. Gravity and support

forces) (2 words – 5,5)14. The type of contact force that always acts in the opposite direction to movementDOWN1. The force of gravity acting on a mass2. The amount of matter in an object – constant anywhere

in the universe3. The speed in a particular direction (measured in

metres per second)4. Force pairs that result in an acceleration6. Occurs when a force is moved a distance. Measured in

Joules7. The SI units for Force8. Can easiest be described as a push or a pull10. A type of Force contained by a charged object – seen

in the van der Graaf machine on the right


Acceleration- a change in velocity

1. Fill in the gaps in the following sentences.

Objects that move at the same speed in the same direction are said to have a

c____________ v_____________. This means that their velocity does not change and a

graph of d__________ vs t____________ would have a straight line drawn on it. If an object like a car changes its velocity and speeds up the driver would have pressed down on the

accelerator. This ‘speeding up’ is called a__________________. If the driver slows down

using the brakes the car d___________________ ( this is the same as a negative

a________________). Both the a__________________ and the d__________________ of the car was caused by applying a force. Engine push force in the case of the

a________________. Braking friction force in the case of the d____________________.

Measuring and calculating Acceleration


2. Plot the following data onto a Velocity vs time graph. Time on the bottom axis. 9 km hr –1 means the same as km / hr or kilometres per hour ( the speed of the car at 2 second intervals as it accelerated

3. You will notice that there are two distinct parts to the graph. Calculate the gradient for each part. The units this time are m/s divided by s so the unit for the acceleration is m/s2.First part. a = _______ ____ Second part. a = ________ ______

=_______ _____/ ___ = ______ ___/ ___

The a______________ of

an object is given by the

g_____________ of a

v_____________ vs

t__________ graph. It can also be calculated using the formula-

a = change in velocity

time

Types of Forces

1. Fill in the gaps of the following sentences.

A Force is defined as a p_________ or a p_______. They can act by directly touching an

object and are called c___________ f__________s. There are also three types of force that act at a distance without having to touch an object.

2. Below each type of force write if it acts on contact or acts at a distance.pull kick push friction gravity

buoyancy electrostatic reaction magnetic lift

3. Fill in the gaps of the following sentences.

The energy of a moving object is transformed from kinetic energy into heat energy as it slows

down. The force that slows things down is called f____________ and it always acts in the

o________________ direction to the direction an object moves in.

4. Force Fields surround some objects and account for the three types of Force that act at a distance. Practice drawing the Force Field Lines around the three objects below. (Remember that the Force Field Lines have arrows indicating a pull force. Gravity goes toward the Earth. A positive charge moves toward a negative Van de Graaf, A North Pole would travel toward a South Pole).

Gravity Force Field lines around the Earth

Electrostatic Force Field Lines around the negatively charged Van de Graaf

Magnetic Force Field lines around a bar magnet.


N

S

Earth

Earth

Drawing Forces PracticeFree Body Force Diagrams are a tool to help you think clearly about each force.

1. Follow the rules and draw a Free Body Force Diagram of the shark floating still in the water.

Rules for drawing Free Body Force Diagrams0.2 kilogram apple sitting on a plate sitting on a table

A 250 kg dolphin floating in the water.

1. Only one object is shown in the diagram.

2. All Forces are shown using arrows. Arrows show the direction AND by their length the size of the force.

3. Force arrows touch the diagram where the force is acting.

4. Forces are labelled using a description of what the type of force is. eg FFriction, Fpush,

5. Forces are measured in units called Newtons ( N ) and written on the diagram.

Types of Force: FFriction, Fpush, Fpull,

Fthrust, Fgravity, Fweight, Fair resistance, Fdrag,

Fmagnetic, Fsupport, Fbouyancy, Felectrostatic,

Freaction.

Draw the Free Body Force Diagram of the dolphin here.

2. In both the diagrams above the object is not moving and the force arrows you have drawn are exactly the same length pointing in opposite directions. These two forces cancel each other out and the object remains still. The Action Force is the Fgravity, the Reaction Force is what stops the object moving. Fbouyancy in the case of the dolphin. This pairing of forces is

called an A________ F________ - R____________ F________ pair and is very common.


3. Sketch a Free Body Force Diagram for this bloke standing on some scales.

Drawing and Calculating Forces PracticeFweight always acts downwards toward the centre of the mass that is doing the attracting. The bigger the mass that is doing the attracting the bigger the force of attraction. The moon is 1/6th the mass of the Earth so its Force of gravity is 1/6th that of the Earth. 1. The Fweight is drawn for you on the diagram below. The astronaut is stationary. Draw in the reaction force on each diagram and write beside the arrow what the reaction force must be equal to.

2. Fill in the gaps in the following sentences. Fweight is different depending on which planet you are on BUT your m__________ stays

c_____________. Force is measured in N________ and its symbol is ___. It is calculated

using the equation F = ma. ‘F’ is short for _________. ‘m’ is short for _______.

‘a’ is short for __________________.

Mass is the amount of m___________ in an object and is different to w____________.

W____________ is the F__________ of G____________ acting on the mass.

3. For each of the stationary objects on the Earth listed, calculate their Fweight and the FReaction (reaction force) that is keeping them still. The acceleration due to gravity downwards on Earth ( a in F = ma ) is the same for all masses and is 10 m/s2.

Object mass ( kg) Fweight = ma FReactionStone sitting on the ground.

20

Car standing at a set of traffic lights

850

Hot air Balloon floating stationary

540

You sitting here doing this homework.

My mass is

______ ___

2. How much mass do you have? Sounds a silly question but it is asking for an answer in kilograms. “I have a mass of ______ kg.”

3. How much do you weigh? In science Weight is a force so you should reply by multiplying your mass by 10 and answer in Newtons. “I weigh _______ N “


am

F

MoonEarth JupiterFweight = 110 N

Fweight = 700 NFweight = 3600 N

More Balanced Forces

Imagine you are riding along on your bike. You are applying a Fpush to the pedals. You feel wind in your face. There is a Fdrag and it is against you. In order to go faster you apply more Fpush to the pedals. The wind in your face gets stronger and you end up going at a constant velocity. This is a general Law if an object is travelling at a constant velocity or is stationary all forces are equal and opposite.

1. Draw and label the missing force arrows on the Free Body Force Diagrams below. ( Remember the second diagram has larger Fdrag arrows because the bike is travelling faster but at a constant velocity.)

A bike and riders ( m = 150 kg ) travelling at a constant velocity of 2 m/s

A bike and riders ( m = 150 kg ) travelling at a constant velocity of 4 m/s

2. Fill in the gaps in the following sentences.

If forces are e________ and o______________ they are said to be a balanced A_________

F__________ - R____________ F_________ pair. The object will either remain

s_____________ or continue at a c______________ v________________. This means that

no change in v____________ occurs so the object does not a_________________.

3. Forces are not always equal and opposite. If they are not, we see an object changing its velocity. It accelerates. A ball that is dropped from a hand, no longer has a Freaction up from the hand that was holding it up. It falls toward the ground faster and faster, it accelerates because there is still the Force of Gravity down. All masses accelerate downwards on Earth at 10 m/s2 if air resistance is very small.

Draw the Free Body Force Diagram of the 1.2 kg ball dropping through the air.


Fdrag = 60 N Fdrag = 120 N

Fweight = 1500 N

Freaction = _______ N

Fweight = 1500 N

Fpush = ______ N Fp___ = ______ N

Fr______ = _______ N

4. As the ball gains velocity the air resistance force up slowly increases. There is still an unbalanced force downwards so it accelerates downwards in the direction of the unbalanced force.a) What is the Fweight of the 1.2 kg ball? ____Nb) If there is a 1 N force up, what is the unbalanced force down? ____N Fw______ = _____ N

Fa__ r_________ = 1 N

Unbalanced Forces1. Fill in the gaps in the following sentences.

If F_______ are not e_________ and o______________ an object will

a_______________. The Net Force can be calculated by drawing a

F______ B_______ F_________ D__________. When this Net F________ is put into the

rearranged equation F = ma the objects a________________ can be calculated if its

m__________ is known.

2. The Newton’s Law equation is F = ma. a) ‘F’ is short for _____________ and is measured in N____________.

b) ‘m’ is short for ___________ and is always measured in _______________.

c) ‘a’ is short for _______________ and is always measured in ____ / _____.

3. By covering up the ‘m’ with your finger you can rewrite the equation to work out for mass. Repeat the process for ‘a’.

Write out the rearranged equation both in symbols and in words below

Symbols Words

m = ___ m__________ = ____________________

a = ____ a___________________ = ____________________

2. Use the diagrams below to calculate the Net Force. Then use that to calculate the object’s acceleration using the equation. ( in this case the Fweight and the Freaction have been left off the diagrams so they are not complete Free Body Force Diagrams)

Object Net Force Objects acceleration

Fnet = 40 - 20 = 20 N

Fnet = 12 + 12

= ____ N

Fnet = ______

= _________

Fnet = ___________

= ___________


F

m a

a = = = _____ m/s2

10 kg

1 kg

2.5 kg

24 kg

a = = 24

= _____ m/s2

a = = ______

= _____ __/__

a = = ______

= _____ __/__

Friction- Both a problem and a necessary effect.

Fill in the gaps and answer the questions that follow.

3. Each of the pictures below has an example of friction either being helpful or a problem. Explain what is going on in the pictures.

Picture What is going on Picture What is going onSole of a sports shoe A Hydrofoil boat riding up

on its skis

A Hovercraft riding on a cushion of air.

A spacecraft as it enters the atmosphere from space

A roller bearing A boy slips on a banana skin


‘Curling’ is a bizarre sport carried out in frosty Otago on a frozen lake. The stone is hurled down and like lawn bowls it is meant to stop in a circle.1. A Fpush is applied to the stone so it

changes v_______________. It

a_________________. Once the stone has left the thrower’s hand, does it:-a) Continue to accelerateb) Keep going at a constant velocityc) Immediately stops_______________________

2. The stone moves away from the thrower at a c____________ v____________ if there is

no force opposing the motion. We call this opposing force F___________. Why are there two people sweeping water off the ice in front of the stone as it moves?____________________________________________________________________________________________________

Work done.

2. Complete the following table by calculating how much Work would be done on the following bits of steel at the same yard.

Mass of steel ( kg) Fweight (N)Height lifted to

(m)Joules of Work done

on the steel ( J )20 200 5 1000

120 1200 5250 10150 18

3. You also use a force to get an object to move along the ground. Obviously it takes more effort ( Force ) to push a bus than a bike. If each of the vehicles below is pushed 5 m use the Fpush given to calculate the Work done on each vehicle.

Bike Motorbike Car Bus

Fpush ( N )150 350 1000 15000

distance ( m ) 5 5 5 5W ( J )

4. Levers are very effective Force multipliers. They are able to multiply Forces because of the Energy Conservation Law. Fill in the gaps in the following Law . “ E________ can not be c___________ or d_____________ it is only t________________ from one type to another.”


F1d1 = F2d2

=> F1d1 = F2

d2

=> 10 x 1 = _______ N. 0.1 10 times bigger force.

W

dF

If a piece of steel is lifted up a distance the steel stores the energy it has gained as Gravitational Potential Energy. The magnet had to use a Flift over a distance to get the steel to the height required. The gain in energy of the steel is exactly the same as the Work done on the steel W = Fd (Work done equals force times the distance it is lifted to). Remember Energy is measured in Joules and so is Work done.

The bit of steel being lifted in the picture has a mass of 150 kg. It therefore has a Fweight of 150 x 10 = 1500 N. The force to lift it must be at least this if the bit of steel is going to lift.

1. Use the formula W = Fd to work out the energy gained by the bit of steel if it rises 3 m. (Work done on the bit of steel) W = Fd

= __________ x _____

= _________ ____

If the lever on this side of the fulcrum is pushed down with a force the other side of the lever rises a distance and can apply a force upwards. Work Done is the same on both sides because energy is conserved. So F1d1 = F2d2. Calculate the extra force exerted at the other side of the lever in the diagram.

F2 = _______Nd2 = 0.1 m

F1 = 10 Nd1 = 1 m

fulcrum

Height = 3 m

Definitions PracticeIn the space beside each of the words in the following list, select a definition from the list below and write it out.acceleration

Action Force - Reaction Force pairsconstant velocity

Electrostatic Force FieldF weight

Force

friction force

Joules

kilograms

mass

Newtons

unbalanced force

velocity

weight

work done

Definitions Lista Another term for the Force of Gravity acting on a mass.b A contact Force that always acts in the opposite direction to movement.c A force field made around a charged object.d A push or a pulle The SI unit Energy and Work done is measured in.f A change in velocity divided by timeg A velocity that does not change.h The unit Force is measured ini An unequal Action Force- Reaction Force pair results in this force and the mass

accelerates.j A pair of forces that act in opposite directions opposing each other.k A speed in a particular direction that is measured in metres per second.l The SI unit mass is measured in.m The amont of energy transferred to an objectn The amount of matter in an objecto Force of Gravity acting on a mass


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