forces powerpoint revision - island...
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Syllabus: Movement and position use the following units: kilogram (kg), metre (m),
metre/second (m/s), metre/second2 (m/s2), newton (N), second (s) (P1.1).
understand and use distance–time graphs (P1.2) recall and use the relationship between average speed,
distance moved and time average speed = distance moved / time taken (P1.3) recall and use the relationship between acceleration, velocity
and time acceleration = change in velocity / time taken a = (v-u)/t (P1.4) interpret velocity–time graphs (P1.5) determine acceleration from the gradient of a velocity–time
graph and the distance travelled from the area between the graph and the time axis (P1.6).
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Syllabus Double Award express a force as a push or pull of one body on another identify various types of force (e.g. gravitational, electrostatic, etc.) understand that friction is a force that opposes motion recall and use the relationship between unbalanced force, mass and
acceleration: force = mass × acceleration F = m × a recall and use the relationship between weight, mass and g : weight = mass × g W = m × g describe the forces acting on falling objects and explain why falling
objects reach a terminal velocity describe the factors affecting vehicle stopping distance including
speed, mass, road condition and reaction time recall and use the relationship between the moment of a force and its
distance from the pivot: moment = force × perpendicular distance from pivot recall that the weight of a body acts through its centre of gravity describe how extension varies with applied force for helical springs,
metal wires and rubber bands recall that the initial linear region of a force – extension graph is
associated with Hooke’s law
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Syllabus Separate Science express a force as a push or pull of one body on another identify various types of force (e.g.
gravitational, electrostatic etc) distinguish between vector and scalar quantities appreciate the vector nature of a force add forces that act along a line understand that friction is a force that opposes motion recall and use the relationship between unbalanced force, mass and acceleration
force = mass × acceleration F = m × a
recall and use the relationship between weight, mass and g : weight = mass × g W = m × g
describe the forces acting on falling objects and explain why falling objects reach a terminal velocity
describe the factors affecting vehicle stopping distance including speed, mass, road condition and reaction time
recall and use the relationship between the moment of a force and its distance from the pivot: moment = force × perpendicular distance from pivot
recall that the weight of a body acts through its centre of gravity recall and use the principle of moments for a simple system of parallel forces acting in one plane understand that the upward forces on a light beam supported at its ends vary with the position of
a heavy object placed on the beam describe how extension varies with applied force for helical springs, metal wires and rubber bands recall that the initial linear region of a force - extension graph is associated with Hooke’s law
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Speed vs. Velocity
Speed is simply how fast you are travelling…
Velocity is “speed in a given direction”…
This car is travelling at a speed of 20m/s
This car is travelling at a velocity of 20m/s east
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Speed Definition:
The rate of change of distance Equation:
speed = distance time
Units: m/s
Symbol: v (final) or u (initial)
Mnemonic: Xylophones are Very Terrible
x
tv
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Acceleration 07/05/23 Definition:
How quickly velocity changes Equation:
acceleration = (final velocity – initial velocity) ÷ time a =(v-u)
t Symbol: a Units: m/s2
Mnemonic: A Changing Vulture
undergoes Therapy
v-u
ta
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•a stationary object•An object with a fast constant velocity•An object with a slow constant velocity•an object which is accelerating
•The gradient of a distance time graph is its velocity•ie distance divided by time
x
t
x
t
x
t
x
t
Distance Time Graphs
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•An object with a constant velocity•An object with a fast constant acceleration•An object with a slow constant acceleration•an object which has a changing acceleration
•The gradient of a velocity time graph is its acceleration•ie velocity divided by time
v
t
v
t
v
t
v
t
Velocity Time Graphs
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Calculating Distance Travelled
Sketch the graph in your books and write the answers
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Definition Symbol
Unit
How far an object has movedHow fast an object is travelling initially
final velocitya
Mnemonic EquationXylophones are Very TerribleA Changing Vulture undergoes Therapy
Distance Time GraphsGradient = _____________
Velocity Time GraphsGradient = ___________, Area under = ____________
x(m)
t (s)
10
10
15
5
D
E
00
5
G
v (m/s)
t (s)
10
10
15
5
F
00
5
K
v (m/s)
t (s)
10
10
15
5
HI
00
5
Description
Speed
A
B
C
C
x (m)
t (s)
10
10
15
5
A
B
00
5
Description
Speed
D
E
Description
a
F
G
Description
a
H
I
K
Distance Travelled =
Distance Travelled =
Bv (m/s)
t (s)
A
C
DE F
The graph is of a sky diver, describe what is happening:________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________
Worksheet
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Definition Symbol
Unit
distance How far an object has moved x minitial velocity
How fast an object is travelling initially
u m/s
final velocity How fast an object is travelling finally
v m/s
acceleration Change in velocity a m/s2
Mnemonic EquationXylophones are Very Terrible x = v tA Changing Vulture undergoes Therapy a = (v-u)/t
Distance Time GraphsGradient = Velocity
Velocity Time GraphsGradient = acceleration, Area under = distance
x(m)
t (s)
10
10
15
5
D
E
00
5
G
v (m/s)
t (s)
10
10
15
5
F
00
5
K
v (m/s)
t (s)
10
10
15
5
HI
00
5
Description
Speed
A Constant v
2 m/s
B Stationary 0 m/sC Coming
Back Constant v
-2 m/s
C
x (m)
t (s)
10
10
15
5
A
B
00
5
Description
Speed
D Constant v
0.5 m/s
E Faster constant v
1 m/s
Description
a
F Constant v 0 m/s2
G Decelerating
-2 m/s2
Description
a
H Constant a 1 m/s2
I Stationary 0 m/s2
K Constant a 1 m/s2
Distance Travelled = 125 m
Distance Travelled = 75 m
Bv (m/s)
t (s)
A
C
DE F
The graph is of a sky diver, describe what is happening:At A he is accelerating due to his weight, as his speed increases the air resistance increases until at B they balance and he reaches a constant velocity called the terminal velocity. At C he opens his parachute and the air resistance increases causing him to decelerate at D. At E the forces are balanced again and he falls at a new lower terminal velocity until at F he lands
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Drawing Vectors
Small Force
Going Right
Big Force
Going Right
Tiny Force
Going Left
Huge Force
Going Down
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Cardsort: Types of Forces• Upthrust:
• upwards force on a body caused by the water being displaced around it. This is sometimes called buoyancy.
• Lift: • upwards force on an aeroplane.
• Thrust: • forwards force created by a body.
• Weight: • Force due to gravitational attraction.
• Friction:• Force caused by rubbing of surfaces that opposes motion.
• Air/Water Resistance:• Frictional Force caused by particles colliding with the body that
opposes motion.• Magnetic:
• Force caused by magnetic attraction.• Electrostatic:
• Force caused by attraction between charges.• Reaction:
• Force created by a body as a reaction to a force being applied.
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Newton’s First Law Definition:
An object will remain at rest or at a constant velocity in a straight line unless there is a resultant force acting on it.
Isaac Newton 1643-1727
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Newton’s Second Law• Definition:
• The net force acting on a body is directly proportional to the mass x the acceleration of the body and acts in the same direction.
• Equation: • F = m x a• N kg m/s2
• Mnemonic:• Fear my anger
Isaac Newton 1643-1727
F
am
If the forces acting on an object are unbalanced then the object will accelerate, like these wrestlers:
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Gravitational Field Strength• Definition
• Acceleration due to a gravitational field. Can be measured in N/kg or m/s2.
• Is 10 N/kg on Earth.• Symbol:
• g• Equation:
• W = m x g• N kg m/s2
• Mnemonic:• Wow my goodness• Wazzup my G
W
gm
Worksheet
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• Friction always acts in the opposite direction to the way an object is moving.•What is the direction of friction for the following moving objects?
Direction of Friction
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Thinking Distance
Braking Distance
Stopping Distance
Stopping Distance =
= Thinking Distance +
Braking Distance
+
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Factors affecting stopping distances
Copy into your book and add:mass of the car
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Moments a moment is a turning force about a point. moment about a point = force x distance If an object is balanced the sum of the moments on it must add
up to zero. Moments clockwise = moments anticlockwise
“Give me a place to stand and I will move the Earth”
Archimedes(287 – 212 BC)
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Drag and drop any of the masses onto the “see – saw” and try to get it to balance. The masses are in kilograms and the distance in metres.
Principle of MomentsSeparate Science
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Centre of Gravity The weight of an object acts through the centre of
gravity. If you balance an object the moments on it are zero. Therefore the centre of gravity must be at the pivot
point when balanced
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Load (N)
Extension (cm)
Load extension
Elastic limit
Plastic region
Extension of a metal
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Mnemonic Equation UnitsFear my AngerWow my GoodnessMoment = _______ x ________
Stopping distance = ______________ + ______________
Force Descriptionupwards force on a body caused by the water being displaced around
it..upwards force on an aeroplane.
forwards force created by a body.Force due to gravitational attraction
Force caused by rubbing of surfaces that opposes motionFrictional Force caused by particles colliding with the body that
opposes motionForce caused by magnetic attraction.
Force caused by attraction between chargesForce created by a body as a reaction to a force being applied.
Thinking Distance Braking Distance
Load (N)
Extension (cm)
________________________________
______ limit______region
• Definition: • A force is a
_____, _____ or _____ that can cause a change in motion, shape, or direction.
• Symbol:• F (_______)• W (_______)
• Units: • N (_______)
Worksheet
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Force Description
Upthrust upwards force on a body caused by the water being displaced around it..
Lift upwards force on an aeroplane.Thrust forwards force created by a body.Weight Force due to gravitational attractionFriction Force caused by rubbing of surfaces that opposes motion
Air/Water Resistance
Frictional Force caused by particles colliding with the body that opposes motion
Magnetic Force caused by magnetic attraction.Electrostatic Force caused by attraction between charges
Reaction Force created by a body as a reaction to a force being applied.Mnemonic Equation UnitsFear my Anger F = m a N = kg m/s2
Wow my Goodness W = m g N = kg N/kgMoment = force x distance Nm = N mStopping distance = braking distance + thinking distance m
Thinking Distance Braking DistanceSpeed of Car Speed of Car
Tiredness Tyre ConditionsAlcohol Brake Conditions
Drugs and Medicines Road ConditionsDistractions (mobiles) Weather Conditions
Mass of Car
Load (N)
Extension (cm)
Load extensionHooke’s Law is Obeyed
Elastic limit
Plastic region
• Definition: • A force is a
push, pull or twist that can cause a change in motion, shape, or direction.
• Symbol:• F (force)• W (weight)
• Units: • N (newton)
Find the Resultant Force: