Forces and Motion
Physics 1 Velocity and Acceleration
●The velocity of an object is its speed in a given direction
●The acceleration of an object is given by the equation:
a is the acceleration in metres per second squared, m/s2.
v is the final velocity in metres per second, m/s.
u is the final velocity in metres per second, m/s.
t is the time taken in seconds, s.
Physics 2 Motion Graphs
●Interpret data from tables and graphs relating to speed, velocity and acceleration.
●The gradient of a distance-time graph represents speed. Candidates should be able to construct distance-time graphs for an object moving in a straight line when the body is stationary or moving with a constant speed.
●Calculation of the speed of an object from the gradient of a distance-time graph
●The gradient of a velocity-time graph represents acceleration
●Calculation of the acceleration of an object from the gradient of a velocity-time graph
●Calculation of the distance travelled by an object from the area under a velocity-time graph
Physics 3 Resultant Force
●Whenever two objects interact, the forces they exert on each other are equal and opposite.
●A number of forces acting at a point may be replaced by a single force that has the same effect on the motion as the original forces all acting together. This single force is called the resultant force.
●A resultant force acting on an object may cause a change in its state of rest or motion. Candidates should be able to determine the resultant of opposite or parallel forces acting in a straight line.
●If the resultant force acting on a stationary object it:
■zero, the object will remain stationary
■non-zero, the object will accelerate in the direction of the resultant force.
●If the resultant force acting in a moving object is:
■zero, the object will continue to move at the same speed and in the same direction.
■not zero, the object will accelerate in the direction of the resultant force.
●The acceleration of an object is determined by the resultant force acting on the object and the mass of the object.
F is the resultant force in newtons, N.
m is the mass in kilograms, kg.
a is the acceleration in metres per second squared, m/s2.
Physics 4 Terminal Velocity
●Evaluate how the shape and power of a vehicle can be altered to increase the vehicle’s top speed
●Draw and interpret velocity-time graphs for objects that reach terminal velocity, including a consideration of the forces acting on the object.
●The faster an object moves through a fluid the greater the frictional forces that act on it.
●An object falling through a fluid will initially accelerate due to the force of gravity. Eventually the resultant force will be zero and the object will move at its terminal velocity (steady speed). Candidates should understand why the use of a parachute reduces the parachutist’s terminal velocity
●Draw and interpret velocity-time graphs for objects that reach terminal velocity, including a consideration of the forces acting o the object.
●Calculate the weight of an object using the force exerted on it by a gravitational force.
W is the weight in newtons, N.
m is the mass in kilograms, kg.
g is the gravitational field strength in newtons per kilogram, N/kg.
Physics 5 Stopping Distance
●Evaluate the effects of alcohol and drugs on stopping distance.
●When a vehicle travels at a steady speed the resistive forces balance the driving force. Candidates should realise that most of the resistive forces are caused by air resistance.
●The greater the speed of a vehicle the greater the braking force needed to stop it in a certain distance. Candidates should understand that for a given braking force the greater the speed the greater the stopping 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)
●A driver’s reaction time can be affected by tiredness, drugs and alcohol. Candidates should appreciate that distractions may affect a driver’s ability to react.
●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. Candidates should understand that ‘adverse road conditions’ includes wet or icy conditions. Poor condition of the car is limited to the car’s brakes or tyres.
Physics 6 Hooke’s Law
●A force acting on an object may cause a change in shape of the object
●A force applied to an elastic object such as a spring will result in the object stretching and storing elastic potential energy. Calculations of the energy stored when stretching an elastic materials is not required.
●For an object that is able to recover its original shape, elastic potential energy is stored in the object when work is done on the object to change its shape
●The extension of an elastic object is directly proportional to the force applied, provided that the limit of proportionality is not exceeded:
F is the force in newtons, N.
k is the spring constant in newtons per metre, N/m.
e is the extension in metres, m.
Physics 1 Velocity and Acceleration
If something is described as ‘fast’ it means that ______
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If something is described as ‘slow’ it means that ______
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Symbol / Quantity / Units / Unit Symbolv
d
t
Rearrange the equation to make d and then t the subject
What is the difference between speed and velocity?
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What does the word ‘accelerate’ mean?
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Symbol / Quantity / Units / Unit Symbola
Δv
t
Rearrange the equation to make Δv and then t the subject
Physics 2 Motion Graphs
Sketch what the distance-time graph and speed-time graph would look like for:
1 An object moving at a constant speed
2 An object that is speeding up
3 An object that is slowing down
What does the word gradient mean?
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Gradients can be calculated using the equation:
The gradient of a distance-time graph gives us ______
The gradient of a speed-time graph gives us ______
The area under a speed-time graph gives us ______
Here are six graphs representing the motion of different objects.
Graph 1
Graph 2
Graph 3
Graph 4
Graph 1
Which sections of the graph show that the object is…
Stationary? ______
Moving at a constant speed?______
Moving with increasing speed?______
Moving with decreasing speed?______
Moving with the greatest speed?______
Calculate the gradient of the line AB______
Calculate the gradient of the line CD______
Calculate the gradient of the line DE______
Graph 2
Which sections of the graph show that the object is…
Stationary? ______
Moving at a constant speed?______
Moving with increasing speed?______
Moving with decreasing speed?______
Moving with the greatest speed?______
Calculate the gradient of the line 0A______
Calculate the gradient of the line AB______
Calculate the gradient of the line CD______
Calculate the gradient of the line DE______
Graph 3
Which sections of the graph show that the object is…
Stationary? ______
Moving at a constant speed?______
Moving with increasing speed?______
Moving with decreasing speed?______
Calculate the gradient of BC______
Calculate the area under the graph______
Graph 4
Which sections of the graph show that the object is…
Stationary? ______
Moving at a constant speed?______
Moving with increasing speed?______
Moving with decreasing speed?______
Calculate the gradient of line W______
Calculate the gradient of line X______
Calculate the gradient of line Z______
Calculate the area under Y______
Physics 3 Resultant Force
If two forces are described as balanced what does this mean? ______
______
If two forces are described as unbalanced what does this mean? ______
______
What does the term ‘resultant force’ mean? ______
______
Symbol / Quantity / Units / Unit SymbolF
m
a
Rearrange the equation to make m and then a the subject
For each of the following situations calculate the resultant force and describe what would happen to the object:
A)The object is initially stationary
Resultant Force: Size ______Direction ______
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B)The object is initially stationary
Resultant Force: Size ______Direction ______
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C)The object is initially stationary
Resultant Force: Size ______Direction ______
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D)The object is initially moving to the right
Resultant Force: Size ______Direction ______
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E)The object is initially moving to the right
Resultant Force: Size ______Direction ______
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F)The object is initially moving to the right
Resultant Force: Size ______Direction ______
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G)The object is initially moving to the left
Resultant Force: Size ______Direction ______
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Physics 4 Terminal Velocity
As an object speeds up the air resistance will ______
Symbol / Quantity / Units / Unit SymbolW
m
g
Rearrange the equation to make m and then g the subject
Below are stages of a parachutist as they travel from plane to ground. For each stage describe how the weight and air resitance compare to each other.
A) A parachutist as they stand in the plane, ready to jump
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B) Immediately after they have left the plane
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C) 20 seconds after they have left the plane and are falling through the air
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D) When the parachutist stops accelerating and travels at a constant speed
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E) When the parachute first opens
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F) When the parachutist reaches terminal velocity again
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G) When the parachutist is stood on the ground.
______
Sketch a velocity-time graph for the parachute jump. Add labels for the stages A to G.
Physics 5 Stopping Distances
When the brakes of a vehicle are applied and it comes to rest where does the energy go and what effect does it have?
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The overall stopping distance of a vehicle is given by the equation:
Explain what is meant by thinking distance
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Explain what is meant by braking distance
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If the driver’s reaction time was reduced what effect would this have on the stopping distance?
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List the factors that can affect the thinking distance and for each one explain how it affects it (e.g. increases distance).
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List the factors that can affect the braking distance and for each one explain how it affects it (e.g. increases distance).
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What can affect both the thinking and braking distance?
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Physics 6 Hooke’s Law
When a force acts on a spring (because a mass is hung on it) it will stretch. Which type of energy will it now have?
______
The extension is directly proportional to the force applied. What does directly proportional mean?
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How could you tell that an object follows Hooke’s law from a graph of force (y axis) against extension (x axis)?
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What would the graph look like if you replaced the original spring with a spring of larger spring constant?
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How can you find the spring constant from the graph?
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What is the point called when the force and extension are no longer directly proportional?
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Describe the energy changes that happen as a bungee jumper travels from their highest to lowest point.
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Why doesn’t the bungee jumper reach the same higher as they jumped from?
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Symbol / Quantity / Units / Unit SymbolF
k
e
Rearrange the equation to make k and then e the subject
Energy and Momentum
Physics 7 Work Done and Power
●When a force causes an object to move through a distance work is done.
●Work done, force and distance moved are related by the equation:
W is the work done in joules, J.
F is the force applied in newtons, N.
d is the distance moved in the direction of the force in metres, m.
●Energy is transferred when work is done. Candidates should be able to discuss the transfer of kinetic energy in particular situations. Examples might include shuttle re-entry or meteorites burning up in the atmosphere.
●Work done against frictional forces.
●Power is the work done or energy transformed in a given time:
P is the power in watts, W.
E is the energy transferred in joules, J.
t is the time taken in seconds, s.
Physics 8 Kinetic and Potential Energy
●Gravitational potential energy is the energy that an object has by virtue of its position in a gravitational field.
Ep is the change in gravitational potential energy in joules, J.
m is the mass in kilograms, kg.
g is the gravitational field strength in newtons per kilogram, N/kg.
h is the change in height in metres, m.
Candidates should understand that when an object is raised vertically work is done against gravitational force and the object gains gravitational potential energy.
●The kinetic energy of an object depends on its mass and its speed
EK is the kinetic energy in joules, J.
m is the mass in kilograms, kg.
v is the speed in metres per second, m/s.
Physics 9 Momentum
●Momentum is a property of moving objects:
p is the momentum in kilograms metres per second, kg m/s.
m is the mass in kilograms, kg.
v is the velocity in metres per second, m/s.
Physics 10 Collisions and Explosions
●In a closed system the total momentum before an event is equal to the total momentum after the event. This is called the conservation of momentum. Candidates may be required to complete calculation involving two objects. Examples of events are collisions and explosions.
Physics 11 Car Safety Features
●Evaluate the benefits of air bags, crumple zones, seat belts and side impact bars in cars. This should include ideas of both energy changes and momentum changes
●Evaluate the benefits of different types of braking systems, such as regenerative braking
Physics 7 Work Done and Power
Work is done when a force causes an object to ______
What affects the energy that I use whilst moving a trolley across a floor?
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When work done is ______
Symbol / Quantity / Units / Unit SymbolW
F
d
Rearrange the equation to make F and then d the subject.
When a force causes an object to move across the floor what is work done against? ______
What are the energy transformations as this happens?
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When a force causes an object to move up through the air what is work done against? ______
What are the energy transformations as this happens?
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Calculate the work done when a force of 4N moves a chair by 5.7m across the ground.
How high could 90 J raise a box of weight 1.2 kN?
Symbol / Quantity / Units / Unit SymbolP
E
t
Rearrange the equation to make E and then t the subject.
Which of these speakers is the most powerful? Speaker A transfers 3510000 J in 24 hours and speaker B transfers 3.8 kJ in 1 minute 34 seconds?
Physics 8 Kinetic and Potential Energy
What is gravitational potential energy?
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Symbol / Quantity / Units / Unit SymbolEP
m
g
h
Rearrange the equation to make m and then h the subject.
What is kinetic energy?
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Symbol / Quantity / Units / Unit SymbolEK
m
v
Rearrange the equation to make m and then v the subject.
Ford Fiesta1465 kg / Vauxhall Astra
1685 kg / Smart City Coupe
730 kg / Ferrari 360 Spider
1350 kg / Ford Transit Van
1850 kg
Pick two cars from the choice above and calculate the kinetic energy it would have travelling at 14 m/s (around 30 miles per hour).
Now calculate the change in gravitational potential energy when they roll down a hill of height 5 m.
A 70 kg woman sits at the top of a slide 4 m above the ground. Calculate the speed that she will be travelling at when she reaches the bottom of the slide.
She is actually travelling slower than this speed, explain why.
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A man is driving a car with a total mass of 1450 kg at 15 m/s along a flat section of road at the bottom of a hill. If the man turns off the engine at the bottom of the hill what height will he get to?
The car does actually get that high up the hill, explain why.
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Physics 9 Momentum
What is the difference between speed and velocity?
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Symbol / Quantity / Units / Unit Symbolp
m
v
Rearrange the equation to make m and then v the subject.
How can an object travelling at a constant speed have a changing momentum?
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Physics 10 Collisions and Explosions
What does the conservation of momentum mean?
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The diagram shows a car and a van, just before and just after the car collided with the van.
Before the collision / After the collisionWhat is the momentum of the car before the collision?
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What is the momentum of the van before the collision?
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What is the total momentum before the collision?
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What is the total momentum after the collision?
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What is the momentum of the car after the collision?
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What is the momentum of the van after the collision?
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What is the velocity of the van after the collision?
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What assumption have you made during these calculations?
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The picture shows two teenagers riding identical skateboards. The skateboards are moving at the same speed and the teenagers have the same mass.
Why don’t the teenagers have the same momentum?
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One of the skateboarders slows down and stops. The teenager then jumps off the skateboard, causing it to recoil and move in the opposite direction
The teenager, of mass 55 kg, jumps off the skateboard at 0.4 m/s causing the skateboard to recoil at 10 m/s.
What is the total momentum before the jump? ______
What is the total momentum after the jump? ______
What is the momentum of the teenager?
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What is the momentum of the skateboard?
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What is the mass of the skateboard?
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Physics 11 Car Safety Features
How do the side impact bars of a vehicle protect passengers?
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Air bags, crumple zones and seat belts all keep passengers safe by the same basic principle; they reduce the force the passengers
experience by ______
for the momentum of the vehicle and passengers to ______
The front crumple zone of a car is tested at a road traffic laboratory. This is done by using a remote control device to drive the car into a strong barrier. Electronic sensors are attached to the dummy inside the car.