# P4

P4 module

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## Speed and Velocity

Speed = how fast an object is moving.

Instantaneous speed = speed of an object at a particular point in time.

Speed (M/S) = Distance travelled (M) / time taken (S)

Velocity = describes an object's speed and direction

The gradient of a velocity-time graph represents how quickly an object is increasing in speed.

Steeper the slope = faster the speed is increasing

Velocity-time graphs are used in lorry tachographs to make sure that drivers rest regularly and dont exceed speed limits.

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## Forces

Forces = occurs when two objcts interact with each other

Forces in an interatction pair are equal in size and opposite in direction

Gravity = force of attraction between all masses

Air Resistance = air tries to slow an object down

Reaction of the Surface = an object is pulled down onto the surface by gravity and the surface pushes up onto the object with equal force

Friction = the force that tries to stop two objects moving as they slide past one another

Resultant force = overall effect of adding or subtracting forces

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## Distance-time graphs

The gradient of a distance-time graphs represents the speed of an object.

Steeper the slope = greater the speed

To calculate speed using a distance-time graph

-Take any two points on the gradient

-Read off the distance travelled between these points

-Note the time taken between these points

-Divide the distance by the time

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## Distance-time Graphs continued

Curvey distance-time graphs = speed of an object is changing

Average speed of a curvy distance-time graph = total distance divided by total time

Gradient steeper than dotted line = object travelling faster than average speed

Gradient less steep than dotted line = object travelling slower than average speed

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## Momentum

Momentum = measure of the motion of an object

Momentum (kg m/s) = mass (kg) x velocity (m/s)

Change in momentum (kg m/s) = Resultant force (N) x time for force acts for (s)

Collisions cause a change in momentum

If a change in momentum is spread out over a longer period of time, the resultant force will be smaller.

Increasing time of impact = reduces force of impact

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## Kinetic energy and change in energy

Kinetic energy = the energy an object has because of its movement. it depends on the mass and velocity of an object.

Kinetic energy (J) = 1/2 x mass (kg) x velocity(squared) (m/s)

Change in energy = work done

Gravitational potentional energy= energy an object has because of its mass and height above earth

Object is dropped = GPE decreases = kinetic energy increases

Change in GPE (J) = weight (N) x vertical height difference (m)

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## Work

Work is done by a force to move an object resulting in the transfer of energy

work done on an object = object gains energy

work done by an object = object loses energy

Work done by a force (J) = force (N) x distance moved by force (m)

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