About Thermal (Heat) energy

Heat is given off whenever energy is being used. You can tell if a television has been on by feeling if it is warm. When you run up a flight of stairs you feel warm because you are burning food energy.
What exactly is heat? Heat is the transfer or flow of energy from a hot object to one that is cooler. When you feel a warm object, you are actually feeling thermal energy, which is the movement of molecules that make up the object. An object has more thermal energy when it is warm than when it is cool.
The more thermal energy an object has, the faster its molecules move. These faster moving molecules bump into each other more frequently and spread out as they require more space (decreasing the density of the molecules).
Think of people standing in an elevator. If they started moving around, they would start bumping into each other and need more space. This is essentially what happens when molecules get more energy and start moving around; they spread out.
For the most part, the volume of an object increases as the amount of thermal energy it receives increases. In other words, the molecules in warmer objects are less densely packed than the molecules in cooler objects.
You can't see thermal energy, but you can detect evidence of heat transfer. You might see the air shimmering over a radiator (convection), put your hand on a warm spoon that's been sitting in a hot bowl of soup (conduction), or notice that the sun shine feels warm on your skin (radiation). If you need evidence of thermal energy or heat in your life, just feel your arm. Your body generates heat 24 hours a day!
Therefore, Thermal Energy can be transferred by 3 ways: conduction, convection and radiation. :D