# P4 Revision

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• Created by: ElishaG
• Created on: 15-06-16 18:06
What is speed?
The distance travelled over a period of time.
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What is the formula for speed?
Speed(m/s)=Distance(m) divided by time(s).
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Why is it more useful to know the average speed?
Because it gives an average speed of the journey, not the highest or lowest speed.
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What is instantaneous speed?
Velocity.
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On a distance-time graph, what does the gradient represent?
Speed.
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What do flat sections show on a distance-time graph?
It is stationary(not moving).
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Continue the correlation: The steeper the gradient...
The faster it is going.
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What do 'downhill' sections on a distance-time graph mean?
It's coming back towards the starting point.
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What do curves represent on a distance-time graph?
Acceleration or deceleration.
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What does a steepening curve represent?
Acceleration.
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What does a levelling-off curve represent on distance-time graphs>
Deceleration.
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How do you work out the speed in a distance-time graph?
Vertical divided by horizontal.
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What is a displacement-time graph?
Similar to distance-time graph but is for velocity.
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What can displacement be?What does this mean?
Positive or negative.Means that positive is one direction and negative is the opposite direction.
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What is the definition of displacement?
The distance in a given direction from a starting point at any moment in time.
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What is the difference between speed and velocity?
Speed is a number but velocity has direction too.
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What is instantaneous velocity?
The speed and direction at a given moment in time.
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If somethings velocity is decelerating, what happens to the number?
Becomes negative.
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What is acceleration?
Change in velocity or speed in a certain amount of time.
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What is deceleration?
Negative acceleration.
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On a velocity-time graph, what does the gradient represent?
Acceleration.
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What do flat sections represent on a velocity-time graph?
Moving in straight line at constant speed.
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Complete the correlation: The steeper the gradient..
The greater the acceleration or deceleration.
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What are uphill (/) sections on a velocity-time graph?
Acceleration in a straight line.
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What are downhill(\) sections on a velocity-time graph?
Deceleration in a straight line.
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What is the area under any section of the velocity-time graph equal to?
The displacement (distance) travelled in that time interval.
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What does a curve mean in a velocity-time graph?
Change in acceleration.
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What does a negative velocity mean?
The object is travelling in the opposite direction.
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What is the difference between speed-time graphs and velocity-time graphs?
Velocity graphs have directions.
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What is the formula for calculating acceleration using a velocity-time graph?
Vertical divided by horizontal.
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When do forces occur?
When two objects interact.
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What happens when an object exerts a force onto another object?What is this called?
The other object puts an equal and opposite force in return.Called interaction pairs.
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Even though forces are equal, why can they still cause things to move?
They act on different objects.
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What is a reaction force?
If book is placed on a table, exerts downwards force, table exerts equal and opposite force-a response to the force from the book.
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Give the definition of friction.
When objects are moving relative to each other, both experience a force that opposes their movement.
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What is friction?
A reaction force- happens as a result of something else.
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What are three types of friction?
1)Between solid surfaces that are gripping.2)Between solid surfaces sliding past each other.3)Resistance from fluids.
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Describe friction between solid surfaces that are gripping.
Kind of friction that lets us walk around, friction between shoes and ground lets us push against it and move forwards.
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Describe friction between solid surfaces sliding past each other.
Can reduce sliding friction by putting oil and grease between surfaces e.g. parts of car engine.
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Describe resistance from fluids.
Object moving through fluids has to use force to pass other molecules-causes friction.E.g. air resistance.
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What does the length and direction of arrow show on force diagrams?
Length=size of force. Direction=direction of force.
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If an object is moving at a steady speed, what are the forces like?
Balanced.
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When an object is moving, when is there an overall force?
When it is changing speed or direction.
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What is another word for the overall force?
Resultant force.
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What decides the motion of an object?
Force-decides acceleration, deceleration or steady speed.
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What is acceleration the same as?
Change in velocity.e.g. if a car is going round corner it's acceleration is changing.
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What happens if there is a resultant force on an object?
Speed or direction (or both) changes.
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When will a car accelerate?
When the thrust (driving force) exerted by the car is bigger than the resistance(counter force).
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Complete the correlation: The bigger the resultant force...
..The greater the acceleration.
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What would happen if the driving force was smaller than the resistance?
The car would slow down.
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What is momentum?
How hard it is to stop an object moving- the heavier an object,the harder is is to stop.
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Continue the correlation: The greater the mass of an object..
The greater the velocity, the more momentum the object has.
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If a stationary object has a resultant force of 0, what does this mean?
The object will stay still.
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If a moving object has a resultant force of 0, what does this mean?
Stays at constant velocity and momentum.
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If a resultant force on an object is not 0, what does this mean?
Momentum changes in the direction of the force.
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What changes when a resultant force acts on an object?
Causes change in momentum.
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Complete the correlation: The bigger the force and the longer it acts for..
..The bigger the change in momentum.
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If momentum changes quickly, what will the forces be like?
Very large, more likely to cause injury.
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If momentum changes slowly when in a car e.g. by braking, what will the forces be like?
Small, unlikely to be hurt.
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What do safety features in cars do?
Increase collision time to reduce the forces on the body.
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What are 4 safety features of a vehicle?
1)Crumple zones.2)Air bags.3)Seat belt.4)Helmets.
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Describe crumple zones.
Crumple on impact, increase time taken for car to stop.
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Describe air bags.
Slow you down more gradually.
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Describe seatbelts.
Stretch slightly,increases time taken for wearer to stop.Also, reduces force acting on chest.
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Describe helmets.
Provide padding, that increases time taken for head to stop if it hits something hard.
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What happens when a force moves an object?
It does work and energy is transferred to the object.
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Describe work done.
1)When something moves, something else causes it to.2)The thing that causes it needs energy supply(food,fuel,electricity).3)Then does work by moving object-transfers energy into other forms.4)Energy can be useful or waste.
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How is amount of energy transferred by an object calculated?
Amount of energy transferred (J)= Work done (J)
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What happens if energy is transferred?
The object doing the work loses energy.
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What does anything that's moving have?
Kinetic energy.
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What is kinetic energy?
Energy of movement.
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What does the kinetic energy of something depend on?
The mass and speed- greater the mass and faster it's going, the higher the kinetic energy.
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What is the formula for kinetic energy?
Kinetic Energy(J)= 1/2 x Mass(kg) x velocity (m/s squared).
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How do you increase something's kinetic energy?
Need to increase velocity-to increase velocity must apply force to it.
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What are you doing if you're applying a force to something?
Doing work.
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True or False- energy cannot be created or destroyed?
True-energy is always conserved, gets transferred into a different kind of energy.
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Why isn't the KE equal to the work done?
Energy is wasted as heat due to friction and air resistance.
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What is GPE?
Energy stored in an object when you raise it to a height against the force of gravity.
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What happens when you lift an object?
The GPE increases as it's raised.
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What happens as an object falls?
Its GPE decreases.
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What do falling objects convert GPE into?
Kinetic energy, further it falls, the faster it goes.
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What is the formula for Kinetic energy gained?
KE gained= GPE lost.
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Why isn't the amount of KE converted the same amount as the GPE?
Some energy is lost as heat due to air resistance.
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## Other cards in this set

### Card 2

#### Front

What is the formula for speed?

#### Back

Speed(m/s)=Distance(m) divided by time(s).

### Card 3

#### Front

Why is it more useful to know the average speed?

### Card 4

#### Front

What is instantaneous speed?

### Card 5

#### Front

On a distance-time graph, what does the gradient represent?

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