How Does Heat Affect Matter?

Contributor: April Stokes. Lesson ID: 10772

When it's hot outside, do you have more or less energy? Do you know particles of matter react to changes in temperature as well? Watch a science video and design your own experiment to learn about it!


Physical Science

learning style
personality style
Otter, Beaver
Grade Level
Middle School (6-8)
Lesson Type
Quick Query

Lesson Plan - Get It!

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Smack! Pow! Excuse Me. Ouch! Hey — quit being so rough!

moving molecules

If you were a particle, the smallest unit of matter, you'd spend all of your time getting knocked around by other particles, and that's on a good day.

  • How do you think particles react to change in temperature?
  • Do you think they move faster or slower when it's cold?
  • What about when things start to heat up?

Particles that make up matter just can't stand still, but they can slow down a bit when they get a little chilly.

  • But what happens when they get hot?

Let's take a look at what happens to the three different states of matter when exposed to heat, and then we will return to the question.

Suppose you were a gas particle, like a helium atom, inside of a balloon.

You'd fly around, bouncing off the sides of the balloon like a trampoline gymnast. Occasionally, you'd bump into another helium atom, and you would send each other off into new directions. It's not too bad; sometimes, it's even kind of fun.

Then, suddenly, a person takes your balloon outside into the bright sunlight. The sun's rays beat down on your balloon, heating you and the other helium atoms and the other particles. The hotter you become, the more energy you have. You and the other atoms start moving faster and faster. You begin hitting into one another and the sides of the balloon harder and more often. As a result, the balloon stretches, or expands. To expand means to get bigger or take up more space.

You start to worry that your balloon will burst, when the same person takes your balloon inside and puts it in the freezer. Ahhh! That's refreshing — but after a little while, you become rather cold. Brrr! It's becoming more difficult to move. Heat flows out of the balloon and into the cooler air in the freezer. The balloon contracts. To contract means to take up less space, or to become smaller.

  • Why is this happening?

Each time you bang into the wall of the balloon, you lose more energy — your energy is transferred to the balloon. With less energy, you and the other atoms move more slowly. You don't have the energy to travel very far or hit the walls very hard.

Now let's see what happens to water molecules when in a similar situation.

Because ice is a solid, you might think it is heavier than water. If this were true, ice would sink when you put it into your favorite beverage.

Water behaves differently than other liquids. As water cools, it contracts like most other liquids, until the temperature reaches about 4°C. At this point, the particles in the water are packed together as tightly as they can get. However, water changes to ice at 0°C. As the water cools from 4°C to 0°C, the water particles form little rings. Because water particles in rings take up more space, an ice cube is actually larger than the water from which it formed.

  • What about liquid mixtures that turn into solids?

Concrete is a mixture that also expands and contracts. When building bridges, metal joints are placed between sections. As the concrete expands, it pushes the metal in those joints into spaces between the metal. This action prevents the concrete from buckling or breaking.

Another use of expansion and contraction is within a thermometer. Liquid mercury expands almost the same amount for every degree of temperature rise. When you heat mercury, the particles become more active and move away from each other. The mercury expands and the column gets taller, indicating a higher temperature on the thermometer. When you cool mercury, the particles move closer together and the column gets shorter.

All matter expands when it is heated and contracts when it cools. Not all matter expands and contracts the same amount. For every one degree the temperature rises, gases expand the most, liquids expand less, and solids expand the least.

  • So what happens to the particles in the opening section (above) when cooled? 
  • When heated?

You don't even need to know what type of matter the particles are making — all we need to know is that when cooled, the particles loose energy and move more slowly, and, when heated, they gain energy and move more quickly.

Let's go practice this concept to help you understand it better!

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