# Work, energy and momentum

• Created by: Holly45
• Created on: 18-03-15 17:47

## Car safety

• brakes do work against the kinetic energy of the car
• the brakes reduce the kinetic energy of the car by transferring heat and sound energy
• cars are designed to convert kinetic energy safely in a crash
• if a car crashes it will slow down very quickly, this will mean that a lot of kinetic energy is converted into other forms of energy in a short time, which can be dangerous

SEAT BELTS:

• stretch slightly increasing the time taken for the wearer to stop
• this reduces the forces acting on the chest
• kinetic energy is absorbed by the seat belt

AIR BAGS:

• slow you down gradually and prevent you from hitting hard surfaces inside the car
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## Momentum and collision

• momentum = mass X velocity
• momentum is the property of moving objects
• the greater the mass of an object and the greater its velocity the more momentum the object has
• momentum has size and direction
• momentum before = momentum after
• forces can cause changes in momentum
• a larger force means a faster change in momentum
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## Forces and elasticity

• work done to an elastic object is stored as elastic potential energy
• any object that can go back to its original shape after the force has been removed is an elastic object
• elastic potential energy is converted into kinetic energy when it returns to its original shape
• extension of a stretched spring is directly proportional to the force applied
• F = K x E (where K is the spring constant)
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## Work and potential energy

• when a force moves an object through a distance, energy is transferred and work it done
• work done = force X distance
• gravitational potential energy = mass X g X height
• gravitational potential energy is the energy that an object has by virtue because of its vertical position on a gravitational field
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## Kinetic energy

• energy of movement
• kinetic energy = 1/2 X mass X speed squared
• kinetic energy transferred is work done
• it needs to be converted into heat energy as friction between the wheels and brake pads
• kinetic energy transferred = work done by brakes
• kinetic energy gained = potential energy lost
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