Energy can be transferred from one object to another by doing work. To do work requires that an agent exert a force on an object over a distance. When work is done, energy is transferred from the agent to the object, which results in a change in the object’s motion (more specifically, a change in the object’s kinetic energy).
An Example of How Doing Work Transfers Energy from One Object to Another
Suppose that a person (the agent) exerts a force on a wheelbarrow (the object) that is initially at rest, causing it to move over a certain distance. Recall that the work done on the wheelbarrow by the person is equal to the product of the person’s force multiplied by the distance traveled by the wheelbarrow. Notice that when the force is exerted on the wheelbarrow, there’s a change in its motion. Its kinetic energy increases. But where did the wheelbarrow get its kinetic energy? It came from the person exerting the force, who used chemical energy stored in the food they ate to move the wheelbarrow. In other words, when the person did work on the wheelbarrow, they transferred a certain amount of chemical energy to the wheelbarrow, causing it to move. As a result, the person’s store of chemical energy decreases and the wheelbarrow’s kinetic energy increases.
Heat is the transfer of energy from a warmer object to a cooler object. For example, a lighted match (higher temperature object) will transfer heat to a large pan filled with lukewarm water (lower temperature object). Note that the actual amount of thermal energy each object has doesn’t matter, as the pan of lukewarm water might have more thermal energy than the match. What is needed for heat transfer to take place is a difference in temperature between two objects. Without this difference, no heat transfer can take place.
Heat can be transferred in three ways: by conduction, by convection, and by radiation.
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! (Taken from KEEP Energy Education Activity Guide “Exploring Heat“).