# How the conversion of thermal energy in the oceans works

## Conversion of energy

### Conservation of energy

To do work, you have to give up energy. But just like money, energy doesn't just go away when it's given off. The energy is going elsewhere! People talk about "using energy", but energy is never used. It just goes into different forms, as shown in the following example.

When energy passes from one form to another, scientists say that energy is converted. The above pictures show a sequence of energy transformations. The last picture shows the conversion of kinetic energy into thermal energy (heat). When the ball hits the wall, the atoms and molecules in the ball and wall move faster, so the materials warm up a little.

With each transformation in the above illustration, the total amount of energy remains the same. This is an example of the law of conservation of energy:

Energy cannot be produced or destroyed, it can only appear in one form or another.

### Loss of energy

The above pictures show the energy conversions as a simple chain. In reality, energy is lost from the system in different phases. For example, muscles convert less than \$ \ smash {\ frac {1} {5}} \$ of the stored energy in food into kinetic energy. The rest is wasted as thermal energy - which is why exercise makes you sweat. And when objects move through the air, some of their kinetic energy is converted into thermal energy due to friction (air resistance). Even the sound is eventually "absorbed", which makes the absorbing materials a little warmer than before.

The diagram below shows how all of the original energy of the bullet thrower ends up as small thermal energy. Despite the apparent loss of energy from the system, the law of conservation of energy still applies. The total amount of energy remains unchanged.

### Work done and energy converted

Whenever work is done, energy is converted. In the figure, for example, a falling ball loses 20 J of potential energy. Assuming that there is no air resistance, this energy is converted into 20 J kinetic energy. So 20 J of work is done to accelerate the ball. When the ball touches the ground and comes to rest, 20 J of kinetic energy is converted into thermal energy. Again 20 J of work are done when the ball hits the ground below.

The following applies in all cases:

Work done = energy converted

 20 J energy in one form 20 years of work done 20 J energy in the other form