# 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?

#### Back

### Card 4

#### Front

What is instantaneous speed?

#### Back

### Card 5

#### Front

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

#### Back

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