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
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