When something is moving it has energy. Imagine trying to stop a run away
horse or a rugby forward moving at speed.
This type of energy is called the KINETIC ENERGY of the object.
It is quite easy to see what
things affect the kinetic energy.
There will be more energy 'locked away' in a massive
lorry that is moving at 20 m/s than in a motorbike travelling at the same speed.
Also the faster it goes the more kinetic
energy the lorry will have.
A lorry moving at high speed will have much more kinetic
energy than a lorry moving at low speed.
Therefore a fast moving car or lorry will cause
more damage in an accident than a slow moving one because this kinetic energy has to be turned
into other forms including sound, heat and stress on the other vehicles.
The kinetic energy
of an object therefore depends on two things:
(a) the mass of the object (m)
(b) its speed
(v)
The formula for kinetic energy of an object of mass m travelling at speed v is:
When an object falls to the ground all its
potential energy changes to kinetic energy (ignoring friction with the air). When it hits the ground
this kinetic energy is changed to sound and heat. However when something slides down a hill it looses potential energy and
gains some kinetic energy. The kinetic energy it gains will always be a little less than the potential
energy it looses, the rest will be lost as sound and heat due to friction.
The rocket shown in the diagram had a huge mass at take
off but because its speed was very low its kinetic energy was low. As the speed increased the
kinetic energy rose rapidly even though the rocket was getting lighter as it burnt fuel.