Kinetic energy and potential energy are both types of work: A body in motion is doing work; a stationary body has the potential to be doing work. The first law of thermodynamics states that energy cannot be created or destroyed but must be transformed from one form to another. A stationery automobile has no kinetic energy but maximum potential energy in the form of chemical potential energy. The burning of fuel in the car's engine releases energy that drives the pistons, causing the car's the wheels to turn. Some of the car's potential energy stored in its fuel has been converted into kinetic energy. If the car was to reach top speed, it would have zero potential energy, as it could not go any faster.
Potential energy can be chemical, elastic or gravitational. A battery in isolation is no use, however when connected to a circuit chemical energy is transformed into electrical energy. A spring is similarly motionless until compressed or extended which will set it in motion. Simply picking up an object increases it gravitational potential energy: Releasing this object will cause it to do work as it falls back to the ground.
There are many different ways to demonstrate energy transfer in the laboratory. One of the simplest methods uses three different types of toy car: one that works with a wind-up mechanism; one that is powered with a battery; and one that has no powering mechanism. The first car will move when its mechanism is wound, demonstrating a change from elastic potential energy to kinetic energy. The movement of the second car is the result of two changes in energy: First the chemical potential energy in the battery is transformed into electrical energy, which is then used to drive the motor to move the car. In the final example, movement of the wrist or arm propels the car.
A body displaying simple harmonic motion is one whose energy is continually changing between kinetic and potential. At rest a pendulum has no kinetic energy, but introducing energy to the system by moving it gives the pendulum potential energy. This energy is then transformed into kinetic energy and then back to potential energy is a continuous cycle.
Extending or comprising a spring gives it potential energy which also sets it into repeating, periodic motion. A body with simple harmonic motion has maximum potential energy when it has minimum kinetic energy and vice versa.