# Entropy Lesson for Kids

Instructor: Shoshana Yarin

Shoshana has taught all grades with an emphasis in science and has a master's degree in science.

Entropy is an essential concept used in a field of science called thermodynamics. In this lesson, we'll learn more about thermodynamics, entropy, and the uses of this concept.

## Thermodynamics and Heat

Have you ever gone down a slide in shorts and it felt like you burnt your skin? Think about when your hands are cold and you rub them together to warm up. These are examples of friction in action. Friction is the result of one thing rubbing against and, in effect, slowing down the motion of another. With friction, some of the energy of the thing in motion gets changed, or transformed, into heat energy, also called thermal energy.

There's a whole field of science, called thermodynamics, that explores this--the way that heat relates to other types of energy, like motion. In fact, some people believe the term comes from the Greek therme (heat) and dyanims (power). And one very important aspect of thermodynamics is entropy.

## What is Entropy?

Entropy is a measure of how much the atoms in a substance are free to spread out, move around, and arrange themselves in random ways. For instance, when a substance changes from a solid to a liquid, such as ice to water, the atoms in the substance get more freedom to move around. You can see this by the way that water can slosh around, but ice is a solid object. Because those atoms have more freedom, they're more likely to be randomly arranged. And so, we can say that water has higher entropy than ice.

So, when there is higher entropy, there is greater freedom for atoms to move around. And the more energy we have, the more atoms move around and spread into a random arrangement.

## More on Thermodynamics

Entropy plays a large role in the second law of thermodynamics, which says that atoms tend to become more free and randomly arranged, so that throughout the universe, the level of entropy is rising at a steady rate.

With this law also comes the idea that thermal energy moves from hotter to colder areas as a way of spreading out the heat, but it doesn't flow in the opposite direction (from colder to hotter). Think about when you put a pan on the stove--the heat spreads throughout the pan evenly, even though only a small part of the pan is touching the flame. When you turn the stove off, the heat in the pan doesn't just flow back into the stove; it keeps moving to the colder areas--into the air around it.

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