P2aL8 Energy to Move

Key Words

Energy Transfer Diagram - diagram that shows what energy is transferred to what other kinds of energy.

Frictional forces - force opposing movement caused by surface rubbing against each other.

Kinetic energy - energy in a moving object.

Potential energy - energy stored in a raised object that can do work when it falls.

Transformed - energy converted from one form to another.

Work done - energy expended to do a job.

Grade E

Kinetic energy is energy of movement, coming from a Greek word, "kinein" - to move.  Fuels are converted to kinetic energy in a car engine.  Electrical energy is converted into kinetic energy by the large traction motors of an electric locomotive.  Here is a typical energy transfer diagram.

Of course, kinetic energy can be transformed into other forms of energy:

• work done to deform the bodywork of a crashed car.

• heat in brakes.

In a test to show the toughness of concrete used in nuclear power stations, an aeroplane attached to a rocket sled was slammed into a large block at a speed of 800 km/h.  The aeroplane was vaporised except for the wing tips that flew on.

Grade C

High speed objects travelling through air can get very hot due to friction.  Spacecraft coming back to Earth glow red hot as they pass through the upper atmosphere.  Special heat resistant tiles stop the heat passing to the main body of the craft and frying everyone inside.

Concorde travelling at 600 m/s would get hot enough to expand by 20 cm.

In a swinging pendulum, kinetic energy is turned into potential energy, which is turned back into kinetic energy.  The interchange goes on until the pendulum stops swinging.  This is because some energy is transferred to work done against the small opposing forces of friction and air resistance.

Grade A

While kinetic energy can be stored, its storage is not permanent.  A spinning flywheel will store a lot of kinetic energy, but all the energy has to be put in by a motor of some sort.  When the motor is turned off, the flywheel will continue to spin, but kinetic energy will be lost in the bearings and through drag.  Eventually the flywheel will stop.

The machine below provides a back up power supply, which, in the event of a power cut, provides enough power to allow vital computers to be turned off safely.