All matter is made up of particle or molecules. These molecules are in constant motion. Anything in motion, even particles, has kinetic energy.
Even in a solid object, like ice, these particles are vibrating.
As we add heat, these particles gain extra energy and begin to vibrate more and more. This increases the thermal energy produced by the object.
Thermal energy is measured in Joules (J).
If we have a boiling cup of coffee it is giving off a high amount of thermal energy.
When we add cold milk to the coffee, some of the energy is transferred from the coffee to the milk. This cools down the drink, because the thermal energy is lost to the milk.
By now you’ve probably noticed that thermal energy and temperature are related. However its important to understand that one doesn't equal the other.
If we have a swimming pool at 35 deg Celsius, and a cup of coffee at 80 deg Celsius, the pool has more thermal energy.
This is because there is much more water in the pool than the coffee.
Observe the animation to the left.
Both containers are the same temperature, however when we cut the heat, the larger one takes twice as long to return to room temperature (20 deg). This means the larger one has twice as much thermal energy as the small one.
We can transfer heat from one object to another through Conduction, convection or radiation.
