In the simple everyday events and processes, we identify objects that gain or lose energy. For example, objects slow down or get hotter. There are different ways energy is stored. Hence, it can be said that there are different types of energy stores.
Different types of energy stores – We use the following labels to describe different types of energy stores:
- internal (or thermal)
- gravitational potential
- elastic potential
Energy stores and systems
We can begin to understand energy by studying changes in the way energy is stored when a system changes. A ‘system’ is an object or a group of objects that interact.
Here are some situations with which we are generally familiar where when a system changes the way energy is stored also changes.
Throwing an object upwards
– When we throw a ball upwards, just after the ball leaves our hand it has a store of kinetic energy. When the ball reaches its highest point, it has a store of gravitational potential energy. Just before we catch it again, it has a store of kinetic energy.
Boiling water in a kettle
– When we turn on an electric kettle, the water in the kettle gets hotter. There is now more internal (or thermal) energy stored in the hot water than there was in the cold water.
-When we burn coal there is a chemical reaction. Coal has a store of chemical energy which is transferred to thermal energy as it burns. A coal fire can warm up a room.
A car using its brakes to slow down
– A moving car has a store of kinetic energy. When the car slows to a halt, it has lost this store of kinetic energy. The brakes exert a frictional force on the wheels, and the brakes get hot. The store of kinetic energy in the car has been transferred to a store of thermal energy in the brakes. This energy is then transferred to the surroundings.
Dropping an object which does not bounce
– Just before the object hits the ground, it has a store of kinetic energy. After the object has stopped moving, the kinetic energy has been transferred to a store of internal energy in the object and the surroundings. So the object and the surroundings warm up a little. (We might hear a noise, but the energy carried by the sound is also transferred to the internal energy of the surroundings.)
Accelerating a ball with a constant force
– We have a store of chemical potential energy in our muscles. When we throw a ball, our store of chemical potential energy decreases, and the ball’s store of kinetic energy increases. The hand applies a force to the ball and does work to accelerate it.