Forces,
movement,
shape and
momentum
Paper 1
Forces and
motion
Forces and motion
Forces, movement, shape and momentum
objectives
• 1.11 describe the effects of forces between bodies such as changes in
speed, shape or direction
• 1.12 identify different types of force such as gravitational or
electrostatic
• 1.13 understand how vector quantities differ from scalar quantities
• 1.14 understand that force is a vector quantity
• 1.15 calculate the resultant force of forces that act along a line
• 1.16 know that friction is a force that opposes motion
Forces and motion
Forces, movement, shape and momentum
objectives
•
•
1.17 know and use the relationship between unbalanced force, mass and acceleration:
force = mass × acceleration.
1.18 know and use the relationship between weight, mass and gravitational field strength:
weight = mass × gravitational field strength
•
1.19 know that the stopping distance of a vehicle is made up of the sum of the thinking
distance and the braking distance
•
1.20 describe the factors affecting vehicle stopping distance, including speed, mass, road
condition and reaction time
•
1.21 describe the forces acting on falling objects (and explain why falling objects reach a
terminal velocity)
•
•
1.23 know that the initial linear region of a force-extension graph is associated with
Hooke’s law
1.24 describe elastic behavior as the ability of a material to recover its original shape after
the forces causing deformation have been removed
Scalar and vector quantities recap
Scalars recap
B - describe the forces acting on falling objects (and explain why falling objects reach a terminal velocity). know and use the relationship
between weight, mass and gravitational field strength. calculate the resultant force of forces that act along a line
C - describe the factors affecting vehicle stopping distance, including speed, mass, road condition and reaction time. know and use the
relationship between unbalanced force, mass and acceleration.
D - describe the effects of forces between bodies such as changes in speed, shape or direction.
• A scalar quantity is a quantity that has magnitude only and
has no direction in space
Examples of Scalar Quantities:
▪
Length
▪
Area
▪
Volume
▪
Time
▪
Mass
Vectors recap
B - describe the forces acting on falling objects (and explain why falling objects reach a terminal velocity). know and use the relationship
between weight, mass and gravitational field strength. calculate the resultant force of forces that act along a line
C - describe the factors affecting vehicle stopping distance, including speed, mass, road condition and reaction time. know and use the
relationship between unbalanced force, mass and acceleration.
D - describe the effects of forces between bodies such as changes in speed, shape or direction.
• A vector quantity is a quantity that has both magnitude and a direction
in space
Examples of Vector Quantities:
▪
Displacement
▪
Velocity
▪
Acceleration
▪
Force
What is a force?
Forces
B - describe the forces acting on falling objects (and explain why falling objects reach a terminal velocity). know and use the relationship
between weight, mass and gravitational field strength. calculate the resultant force of forces that act along a line
C - describe the factors affecting vehicle stopping distance, including speed, mass, road condition and reaction time. know and use the
relationship between unbalanced force, mass and acceleration.
D - describe the effects of forces between bodies such as changes in speed, shape or direction.
A force is any influence that causes an object to undergo a specific change
Types of forces
• Contact Force – Forces that act through direct contact between
two objects
Applied Forces, Friction
• Long Range Forces – Forces that can act over distances
Gravity, Electromagnetic Force (EMF)
Types of forces
Newtons laws of motions
Newton’s Laws of Motion
B - describe the forces acting on falling objects (and explain why falling objects reach a terminal velocity). know and use the relationship
between weight, mass and gravitational field strength. calculate the resultant force of forces that act along a line
C - describe the factors affecting vehicle stopping distance, including speed, mass, road condition and reaction time. know and use the
relationship between unbalanced force, mass and acceleration.
D - describe the effects of forces between bodies such as changes in speed, shape or direction.
1. An object in motion tends to stay in motion and an object at rest tends
to stay at rest unless acted upon by an unbalanced force.
2. Force equals mass times acceleration
(F = ma)
3. For every action there is an equal and opposite reaction.
Newton’s First Law
B - describe the forces acting on falling objects (and explain why falling objects reach a terminal velocity). know and use the relationship
between weight, mass and gravitational field strength. calculate the resultant force of forces that act along a line
C - describe the factors affecting vehicle stopping distance, including speed, mass, road condition and reaction time. know and use the
relationship between unbalanced force, mass and acceleration.
D - describe the effects of forces between bodies such as changes in speed, shape or direction.
An object at rest tends to stay at rest and an object in motion
tends to stay in motion unless acted upon by an unbalanced
force.
Newton’s First Law
If no unbalanced forces act on a moving object, then the object will
continue to move with a constant velocity (constant speed in a straight
line). If an object is at rest it will stay at rest.
First Condition for Equilibrium
If the Net Force acting on the object is zero
FNET = 0 a = 0
The object is either stationary (v = 0) or traveling with a constant
velocity (v = constant)
Newton’s First Law
B - describe the forces acting on falling objects (and explain why falling objects reach a terminal velocity). know and use the relationship
between weight, mass and gravitational field strength. calculate the resultant force of forces that act along a line
C - describe the factors affecting vehicle stopping distance, including speed, mass, road condition and reaction time. know and use the
relationship between unbalanced force, mass and acceleration.
D - describe the effects of forces between bodies such as changes in speed, shape or direction.
Basically, an object will “keep doing what it was doing” unless acted on
by an unbalanced force.
If the object was sitting still, it will remain stationary. If it was moving
at a constant velocity, it will keep moving.
Newton’s First Law
B - describe the forces acting on falling objects (and explain why falling objects reach a terminal velocity). know and use the relationship
between weight, mass and gravitational field strength. calculate the resultant force of forces that act along a line
C - describe the factors affecting vehicle stopping distance, including speed, mass, road condition and reaction time. know and use the
relationship between unbalanced force, mass and acceleration.
D - describe the effects of forces between bodies such as changes in speed, shape or direction.
What is meant by unbalanced force?
If the forces on an object are equal
and opposite, they are said to be
balanced, and the object
experiences no change in motion.
If they are not equal and
opposite, then the forces are
unbalanced and the motion of the
object changes.
Newton’s First Law – examples from real life
B - describe the forces acting on falling objects (and explain why falling objects reach a terminal velocity). know and use the relationship
between weight, mass and gravitational field strength. calculate the resultant force of forces that act along a line
C - describe the factors affecting vehicle stopping distance, including speed, mass, road condition and reaction time. know and use the
relationship between unbalanced force, mass and acceleration.
D - describe the effects of forces between bodies such as changes in speed, shape or direction.
A soccer ball is sitting at rest. It takes an unbalanced force of a kick to
change its motion.
Two teams are playing tug of war. They are both exerting equal force on the
rope in opposite directions. This balanced force results in no change of
motion.
Law of Inertia
B - describe the forces acting on falling objects (and explain why falling objects reach a terminal velocity). know and use the relationship
between weight, mass and gravitational field strength. calculate the resultant force of forces that act along a line
C - describe the factors affecting vehicle stopping distance, including speed, mass, road condition and reaction time. know and use the
relationship between unbalanced force, mass and acceleration.
D - describe the effects of forces between bodies such as changes in speed, shape or direction.
Newton’s First Law is also called the Law of Inertia
Inertia: the tendency of an object to resist changes in its state of motion
The First Law states that all objects have inertia. The more mass an object has,
the more inertia it has (and the harder it is to change its motion).
More Examples from Real Life
B - describe the forces acting on falling objects (and explain why falling objects reach a terminal velocity). know and use the relationship
between weight, mass and gravitational field strength. calculate the resultant force of forces that act along a line
C - describe the factors affecting vehicle stopping distance, including speed, mass, road condition and reaction time. know and use the
relationship between unbalanced force, mass and acceleration.
D - describe the effects of forces between bodies such as changes in speed, shape or direction.
A powerful locomotive begins to pull a long line of
boxcars that were sitting at rest. Since the boxcars are
so massive, they have a great deal of inertia and it takes
a large force to change their motion. Once they are
moving, it takes a large force to stop them.
On your way to school, a bug flies into your windshield.
Since the bug is so small, it has very little inertia and
exerts a very small force on your car (so small that you
don’t even feel it).
Newtons first law
B - describe the forces acting on falling objects (and explain why falling objects reach a terminal velocity). know and use the relationship
between weight, mass and gravitational field strength. calculate the resultant force of forces that act along a line
C - describe the factors affecting vehicle stopping distance, including speed, mass, road condition and reaction time. know and use the
relationship between unbalanced force, mass and acceleration.
D - describe the effects of forces between bodies such as changes in speed, shape or direction.
If objects in motion tend to stay in motion, why don’t moving objects keep
moving forever?
Things don’t keep moving forever because there’s almost
always an unbalanced force acting upon it.
A book sliding across a table slows down and stops because
of the force of friction.
If you throw a ball upwards it will eventually slow down
and fall because of the force of gravity.
Newton’s first law
B - describe the forces acting on falling objects (and explain why falling objects reach a terminal velocity). know and use the relationship
between weight, mass and gravitational field strength. calculate the resultant force of forces that act along a line
C - describe the factors affecting vehicle stopping distance, including speed, mass, road condition and reaction time. know and use the
relationship between unbalanced force, mass and acceleration.
D - describe the effects of forces between bodies such as changes in speed, shape or direction.
In outer space, away from gravity
and any sources of friction, a rocket
ship launched with a certain speed
and direction would keep going in
that same direction and at that same
speed forever.
Balanced forces
B - describe the forces acting on falling objects (and explain why falling objects reach a terminal velocity). know and use the relationship
between weight, mass and gravitational field strength. calculate the resultant force of forces that act along a line
C - describe the factors affecting vehicle stopping distance, including speed, mass, road condition and reaction time. know and use the
relationship between unbalanced force, mass and acceleration.
D - describe the effects of forces between bodies such as changes in speed, shape or direction.
If forces are in balance, then they cancel
each other out, and the object behaves as if
there is no force on it at all
When terminal velocity is reached, the
skydiver is falling at a steady speed. The force
of air resistance is exactly balanced by the air
resistance pushing upwards.
Balanced and Unbalanced Forces
Balanced forces:
If the forces acting on an object are balanced then the object will either
remain stationary or continue to move with a constant speed.
Unbalanced forces:
If the forces acting on an object are unbalanced then the object will
change its speed. It will begin to move, speed up, slow down or stop.
Newton’s second law
B - describe the forces acting on falling objects (and explain why falling objects reach a terminal velocity). know and use the relationship
between weight, mass and gravitational field strength. calculate the resultant force of forces that act along a line
C - describe the factors affecting vehicle stopping distance, including speed, mass, road condition and reaction time. know and use the
relationship between unbalanced force, mass and acceleration.
D - describe the effects of forces between bodies such as changes in speed, shape or direction.
Force equals mass times acceleration.
F = ma
Acceleration: a measurement of how quickly an
object is changing speed.
What does F = ma mean?
B - describe the forces acting on falling objects (and explain why falling objects reach a terminal velocity). know and use the relationship
between weight, mass and gravitational field strength. calculate the resultant force of forces that act along a line
C - describe the factors affecting vehicle stopping distance, including speed, mass, road condition and reaction time. know and use the
relationship between unbalanced force, mass and acceleration.
D - describe the effects of forces between bodies such as changes in speed, shape or direction.
Force is directly proportional to mass and acceleration. Imagine a ball of a
certain mass moving at a certain acceleration. This ball has a certain force.
Now imagine we make the ball twice as big (double the mass) but keep the
acceleration constant. F = ma says that this new ball has twice the force of the
old ball.
Now imagine the original ball moving at twice the original acceleration. F =
ma says that the ball will again have twice the force of the ball at the original
acceleration.
What does F = ma say?
B - describe the forces acting on falling objects (and explain why falling objects reach a terminal velocity). know and use the relationship
between weight, mass and gravitational field strength. calculate the resultant force of forces that act along a line
C - describe the factors affecting vehicle stopping distance, including speed, mass, road condition and reaction time. know and use the
relationship between unbalanced force, mass and acceleration.
D - describe the effects of forces between bodies such as changes in speed, shape or direction.
F = ma
Something very massive (great mass) that’s changing
speed very slowly (small acceleration), like a glacier,
can still have great force.
Something very small (small mass) that’s changing
speed very quickly (great acceleration), like a bullet,
can still have a great force.
Net Force
• When Multiple forces are acting on an object. The Net Force is the amount
of force that is left after adding all the forces on the object.
• Net force (FNET) = Resultant Force (FR)
Balanced Forces
Balanced Forces are forces that are equal and opposite so that they cancel out.
10 N East
10 N West
→

Net Force = +10 N + -10 N = 0
Unbalanced Forces
Unbalanced Forces are forces that when added do not
cancel out and cause a change in the motion of the
object.
30 N East 10 N West
→

Fnet = +30 N + -10 N = +20 N East
Newtons third law
Newton’s Third Law
B - describe the forces acting on falling objects (and explain why falling objects reach a terminal velocity). know and use the relationship
between weight, mass and gravitational field strength. calculate the resultant force of forces that act along a line
C - describe the factors affecting vehicle stopping distance, including speed, mass, road condition and reaction time. know and use the
relationship between unbalanced force, mass and acceleration.
D - describe the effects of forces between bodies such as changes in speed, shape or direction.
For every action there is an equal and opposite reaction.
Newton’s Third Law
B - describe the forces acting on falling objects (and explain why falling objects reach a terminal velocity). know and use the relationship
between weight, mass and gravitational field strength. calculate the resultant force of forces that act along a line
C - describe the factors affecting vehicle stopping distance, including speed, mass, road condition and reaction time. know and use the
relationship between unbalanced force, mass and acceleration.
D - describe the effects of forces between bodies such as changes in speed, shape or direction.
For every action there is an equal and opposite reaction.
What does this mean?
For every force acting on an object, there is an equal force acting in
the opposite direction.
Right now, gravity is pulling you down in your seat, but Newton’s
Third Law says your seat is pushing up against you with equal
force. Therefore you are not moving. There is a balanced force
acting on you– gravity pulling down, your seat pushing up.
Newton’s Third Law
B - describe the forces acting on falling objects (and explain why falling objects reach a terminal velocity). know and use the relationship
between weight, mass and gravitational field strength. calculate the resultant force of forces that act along a line
C - describe the factors affecting vehicle stopping distance, including speed, mass, road condition and reaction time. know and use the
relationship between unbalanced force, mass and acceleration.
D - describe the effects of forces between bodies such as changes in speed, shape or direction.
Think about it . . .
What happens if you are standing on a skateboard or a slippery floor
and push against a wall? You slide in the opposite direction (away
from the wall), because you pushed on the wall but the wall pushed
back on you with equal and opposite force.
Why does it hurt so much when you stub your toe?
When your toe exerts a force on a rock, the rock exerts an equal
force back on your toe. The harder you hit your toe against it, the
more force the rock exerts back on your toe (and the more your toe
hurts).
Real life examples of newtons third law
Review
B - describe the forces acting on falling objects (and explain why falling objects reach a terminal velocity). know and use the relationship
between weight, mass and gravitational field strength. calculate the resultant force of forces that act along a line
C - describe the factors affecting vehicle stopping distance, including speed, mass, road condition and reaction time. know and use the
relationship between unbalanced force, mass and acceleration.
D - describe the effects of forces between bodies such as changes in speed, shape or direction.
Newton’s First Law:
Objects in motion tend to stay in motion and objects at rest
tend to stay at rest unless acted upon by an unbalanced force.
Newton’s Second Law:
Force equals mass times acceleration (F = ma).
Newton’s Third Law:
For every action there is an equal and opposite reaction.
Newton’s laws questions
1) A force of 1000N is applied to push a mass of 500kg. How quickly does
it accelerate?
2) A force of 3000N acts on a car to make it accelerate by 1.5m/s2. How
heavy is the car?
3) A car accelerates at a rate of 5m/s2. If it weighs 500kg how much driving
force is the engine applying?
4) A force of 10N is applied by a boy while lifting a 20kg mass. How much
does it accelerate by?
Free Body Diagram (FBD)
B - describe the forces acting on falling objects (and explain why falling objects reach a terminal velocity). know and use the relationship
between weight, mass and gravitational field strength. calculate the resultant force of forces that act along a line
C - describe the factors affecting vehicle stopping distance, including speed, mass, road condition and reaction time. know and use the
relationship between unbalanced force, mass and acceleration.
D - describe the effects of forces between bodies such as changes in speed, shape or direction.
A diagram that looks at all the forces acting on a single object. A force
body diagram (FBD) has all the forces labeled with their magnitude and
direction as well as the motion of the object.
Difference between mass and weight
Mass and Weight
Mass is amount of matter that an object possess. Mass does not change with location.
Weight is the gravitational force that a large body (such as a planet) exerts on another
object.
Weight
• Weight is a Force! It is measured in Newtons.
• Weight = Mass x Acceleration due to Gravity (Newton’s 2nd law)
• W = mg
• Weight does change with location! (“g” will change with location)
Misconceptions about falling objects
Air resistance and terminal velocity
B - describe the forces acting on falling objects (and explain why falling objects reach a terminal velocity). know and use the relationship
between weight, mass and gravitational field strength. calculate the resultant force of forces that act along a line
C - describe the factors affecting vehicle stopping distance, including speed, mass, road condition and reaction time. know and use the
relationship between unbalanced force, mass and acceleration.
D - describe the effects of forces between bodies such as changes in speed, shape or direction.
Terminal Velocity – The maximum speed a falling object reaches when dropped
from rest.
An object reaches terminal velocity when the force of gravity is balanced with the
force of air resistance.
Free Fall – The situation where gravity is the only force acting on an object (Assume
no Air Resistance).
Air Resistance – The force the air applies on a moving object. It attempts to slow
down falling objects (similar to friction).
Falling objects
•
Things fall because of gravity.
• The objects falls through air particles thus creating an air resistance.
•
Air resistance opposes gravity and slows down the falling object
• The greater the surface area the greater the air resistance.
• Air resistance is dependent on the size shape and speed of the falling object
• As a falling objects speed increases so does the air resistance.
• Eventually the air resistance acting in the object is equal to its weight force
• The forces are balanced, and the object is falling at a constant speed or its terminal velocity
Air resistance and terminal velocity
B - describe the forces acting on falling objects (and explain why falling objects reach a terminal velocity). know and use the relationship
between weight, mass and gravitational field strength. calculate the resultant force of forces that act along a line
C - describe the factors affecting vehicle stopping distance, including speed, mass, road condition and reaction time. know and use the
relationship between unbalanced force, mass and acceleration.
D - describe the effects of forces between bodies such as changes in speed, shape or direction.
Eventually the force of Air resistance is equal and opposite to the force
of gravity and the Net Force acting on the falling object is zero.
W = FAR
Therefore FNET = 0
Since the Net Force acting on the object is zero, the object continues to fall but
falls the rest of the way at a constant velocity (Newton’s First Law). This
velocity is called the Terminal Velocity!
Air resistance and terminal velocity
B - describe the forces acting on falling objects (and explain why falling objects reach a terminal velocity). know and use the relationship
between weight, mass and gravitational field strength. calculate the resultant force of forces that act along a line
C - describe the factors affecting vehicle stopping distance, including speed, mass, road condition and reaction time. know and use the
relationship between unbalanced force, mass and acceleration.
D - describe the effects of forces between bodies such as changes in speed, shape or direction.
FNET = 0
and
therefore
F = ma
ay = 0
Object falls with a constant velocity (Terminal Velocity)
Terminal Velocity
Consider a skydiver:
1) At the start of his jump the air resistance is
_______ so he _______ downwards.
2) As his speed increases his air resistance
will _______
3) Eventually the air resistance will be big enough
to _______ the skydiver’s weight. At this
point the forces are balanced so his speed
becomes ________ - this is called
TERMINAL VELOCITY
Terminal Velocity
Now he opens his parachute:
4) When he opens his parachute the air resistance
suddenly ________, causing him to start _____
____.
5) Because he is slowing down his air resistance
will _______ again until it balances his
_________. The skydiver has now reached a
new, lower ________ _______.
Parachute opens – diver
slows down
Velocity-time graph for terminal velocity…
Velocity
Speed
increases…
Terminal
velocity
reached…
Time
New, lower terminal velocity
reached
Diver hits the ground
Stopping, thinking, braking distance
Forces and braking
• When a vehicle travels at a steady speed the resistive forces balance the driving force.
• The greater the speed of a vehicle the greater the braking force needed to stop it in a certain
distance.
• The stopping distance of a vehicle is the sum of the distance the vehicle travels during the
driver’s reaction time (thinking distance) and the distance it travels under the braking force
(braking distance).
• When the brakes of a vehicle are applied, work done by the friction force between the
brakes and the wheel reduces the kinetic energy of the vehicle and the temperature of the
brakes increase.
• A vehicle’s braking distance can be affected by adverse road and weather conditions and
poor condition of the vehicle.
• A driver’s reaction time can be affected by tiredness, drugs and alcohol.
Forces and braking
B - describe the forces acting on falling objects (and explain why falling objects reach a terminal velocity). know and use the relationship
between weight, mass and gravitational field strength. calculate the resultant force of forces that act along a line
C - describe the factors affecting vehicle stopping distance, including speed, mass, road condition and reaction time. know and use the
relationship between unbalanced force, mass and acceleration.
D - describe the effects of forces between bodies such as changes in speed, shape or direction.
When a vehicle travels at a steady speed the resistive forces balance the driving force
For any car travelling at constant velocity, the resultant force
on it is zero.
•
This is because the motive force of its engine is balanced by
the resistive forces (i.e. friction and air resistance) on it.
•
A car driver uses the accelerator pedal (also called the gas
pedal) to vary the motive force of the engine.
•
The resistive forces change to meet to the rise or fall.
Forces and braking
• The greater the speed of a vehicle the greater the braking force needed to
stop it in a certain distance.
The braking force needed to stop a vehicle in a certain distance depends on:
•
the velocity of the vehicle when the brakes are first applied
•
the mass of the vehicle.
We can see this using the equation F = ma in which the braking force is the resultant force.
•
•
The greater the velocity, the greater the deceleration needed to stop it in a certain
distance. So the braking force must be greater than at low velocity.
The greater the mass, the greater the braking force needed for a given deceleration.
Forces and braking
• The stopping distance of a vehicle is the sum of the distance the vehicle travels during the driver’s
reaction time (thinking distance) and the distance it travels under the braking force (braking
distance).
Travel this whilst
thinking about
applying the brakes
Now this when you
actually have your
foot on the brakes
Stopping distance
Forces and braking
• A driver’s reaction time can be affected by tiredness, drugs and alcohol.
• A vehicle’s braking distance can be affected by adverse road and weather conditions
and poor condition of the vehicle.
The faster a vehicle is
travelling, the further it
travels before it stops.
This is because the
thinking distance and the
braking distance both
increase with increased
speed.
Poorly maintained vehicles,
for example with worn brakes
or tyres, take longer to stop
because the brakes and tyres
are less effective.
Tiredness, alcohol and drugs all
increase reaction times. So they
increase the thinking distance
(because thinking distance =
speed x reaction time). Therefore,
the stopping distance is greater.
In adverse road conditions,
for example on wet or icy
roads, drivers have to brake
with less force to avoid
skidding. Stopping distances
are therefore greater in poor
road conditions.
Forces and braking – summary
Stopping distance
The distance needed for a car, travelling at a given speed, to stop (m).
Stopping distance = Thinking distance + Braking Distance
Thinking Distance
Braking Distance
Before we react to a danger our brain takes
time to think. The distance travelled during
this time is the Thinking Distance (m)
Cars don’t stop straight away. They travel a
certain distance from when you start
braking to when they stop. This is the
Braking Distance.
Hooke's Law, elastic and plastic behaviour
• If a material returns to its original size and shape when you remove the forces stretching or deforming it
(reversible deformation), we say that the material is demonstrating elastic behaviour.
• A plastic (or inelastic) material is one that stays deformed after you have taken the force away. If
deformation remains (irreversible deformation) after the forces are removed then it is a sign of plastic
behaviour.
• If you apply too big a force a material will lose its elasticity.
• Hooke discovered that the amount a spring stretches is proportional to the amount of force applied
to it. This means if you double the force its extension will double, if you triple the force the extension
will triple and so on.
Hooke’s law
B - describe the forces acting on falling objects (and explain why falling objects reach a terminal velocity). know and use the relationship
between weight, mass and gravitational field strength. calculate the resultant force of forces that act along a line
C - describe the factors affecting vehicle stopping distance, including speed, mass, road condition and reaction time. know and use the
relationship between unbalanced force, mass and acceleration.
D - describe the effects of forces between bodies such as changes in speed, shape or direction.
Hooke’s law states that the extension of a spring force is
proportional to the force used to stretch the spring.
‘Proportional’ means that if the force is doubled then the extension also
doubles.
The line on a graph of force against extension will be a straight AND go
through the origin.
Hooke’s law
When a material obeys Hooke’s Law, the force is proportional to the
extension of the material.
Force  Extension
Fx
This leads to the equation:
F = kx
Where k is a measure of the stiffness of the sample – the gradient of a force –
extension graph.
Hooke’s law
Stretching Springs
B - describe the forces acting on falling objects (and explain why falling objects reach a terminal velocity). know and use the relationship
between weight, mass and gravitational field strength. calculate the resultant force of forces that act along a line
C - describe the factors affecting vehicle stopping distance, including speed, mass, road condition and reaction time. know and use the
relationship between unbalanced force, mass and acceleration.
D - describe the effects of forces between bodies such as changes in speed, shape or direction.
Experimental procedure:
1. Place the weight holder only on the spring and note the position of the
pin against the metre rule.
spring
2. Add 1N (100g) to the holder and note the new position of the pin.
weights
3. Calculate the extension of the spring.
pin
4. Repeat stages 1 to 3 for 2N, 3N, 4N, 5N and 6N. DO NOT EXCEED
6N.
metre rule
Typical results
B - describe the forces acting on falling objects (and explain why falling objects reach a terminal velocity). know and use the relationship
between weight, mass and gravitational field strength. calculate the resultant force of forces that act along a line
C - describe the factors affecting vehicle stopping distance, including speed, mass, road condition and reaction time. know and use the
relationship between unbalanced force, mass and acceleration.
D - describe the effects of forces between bodies such as changes in speed, shape or direction.
Pin position
with holder
only (mm)
Added weight
or Force (N)
Pin position
with weight
(mm)
Extension
(mm)
450
1
480
30
450
2
509
59
450
3
541
91
450
4
570
120
450
5
601
151
450
6
629
179
Force-Extension Graphs
Force-Extension Graphs
Force -Extension Graph
12
10
Force (N)
8
6
4
2
0
0
0.2
0.4
0.6
Extension
0.8
1
1.2
Force-Extension Graphs
Force - Extension Graph stiffer spring
12
10
Force (N)
8
6
4
2
0
0
0.2
0.4
0.6
Extension
0.8
1
1.2
Question
B - describe the forces acting on falling objects (and explain why falling objects reach a terminal velocity). know and use the relationship
between weight, mass and gravitational field strength. calculate the resultant force of forces that act along a line
C - describe the factors affecting vehicle stopping distance, including speed, mass, road condition and reaction time. know and use the
relationship between unbalanced force, mass and acceleration.
D - describe the effects of forces between bodies such as changes in speed, shape or direction.
A spring of original length 150mm is extended by 30mm by a force of 4N. Calculate the
length of the spring if a force of 12N is applied.
12N is three times 4N
Therefore the new extension should be 3 x 30mm
= 90mm
New spring length = 150mm + 90mm
= 240mm
Elastic limit
B - describe the forces acting on falling objects (and explain why falling objects reach a terminal velocity). know and use the relationship
between weight, mass and gravitational field strength. calculate the resultant force of forces that act along a line
C - describe the factors affecting vehicle stopping distance, including speed, mass, road condition and reaction time. know and use the
relationship between unbalanced force, mass and acceleration.
D - describe the effects of forces between bodies such as changes in speed, shape or direction.
Up to a certain extension if the force is removed the
spring will return to its original length. The spring is
behaving elastically.
If this critical extension is exceeded, known as the
elastic limit, the spring will be permanently stretched.
Hooke’s law is no longer obeyed by the spring if its
elastic limit is exceeded.
The right hand
spring has been
stretched beyond its
elastic limit
Elastic limit
Force against extension
graph if the elastic limit
is exceeded
Force (N)
B - describe the forces acting on falling objects (and explain why falling objects reach a terminal velocity). know and use the relationship
between weight, mass and gravitational field strength. calculate the resultant force of forces that act along a line
C - describe the factors affecting vehicle stopping distance, including speed, mass, road condition and reaction time. know and use the
relationship between unbalanced force, mass and acceleration.
D - describe the effects of forces between bodies such as changes in speed, shape or direction.
elastic limit
0
0
Extension (mm)
Hooke’s law
B - describe the forces acting on falling objects (and explain why falling objects reach a terminal velocity). know and use the relationship
between weight, mass and gravitational field strength. calculate the resultant force of forces that act along a line
C - describe the factors affecting vehicle stopping distance, including speed, mass, road condition and reaction time. know and use the
relationship between unbalanced force, mass and acceleration.
D - describe the effects of forces between bodies such as changes in speed, shape or direction.
Force
Stretching an elastic band
An elastic band does not
obey Hooke’s law.
0
0
Extension
Fill in the blanks
Choose appropriate words to fill in the gaps below:
stretched the
Hooke’s law states that when a wire or spring is _________
extension is proportional to the load
increase in length or _________
force applied.
______
elastic
This law is not obeyed if the spring is taken beyond its ______
permanently
limit after which it will become _____________
stretched.
A ________
rubber band does not obey Hooke’s law.
A graph illustrating Hooke’s law will have a line that is
straight
origin
___________
and passes through the _______.
WORD SELECTION:
stretched elastic permanently extension
origin force rubber straight
Force-Extension Graphs
Force-Extension Graphs
Force-Extension Graphs
Force-Extension Graphs
Force-Extension Graphs
The elastic limit can be seen on the graph.
This is where it stops obeying Hookes law.
Force-Extension Graphs
Newtons third law with a bicycle
Galileo's famous experiment
Forces and motion
Forces, movement, shape and momentum
p1
Past paper questions
Paper 1
13 questions
Question 1
Question 2
Question 3
Question 4
Answer 1-3
Answer 3-4
Question 5
Question 6
Answer 6
Question 7
Question 7
Question 8
Answer 7
Answer 8
Question 9
Answer 9
Question 10
Question 11
Question 12
Answer 10-11
Answer 12
Question 13
Answer 13