Thermal Energy

What do the words hot and cold mean? What does it mean when something feels hot? How do the words hot and warm differ?

The group of friends shown here are spending the day outdoors in the snow. Some of the group is bundled up in thick clothing. However, one of the friends is wearing shorts.

Imagine what would happen if the woman to the right asked her friend if it was cold enough to need a hat outside. He would answer that the weather was comfortable, and she would end up cold on their walk.

Engage

Recall that matter is composed of atoms. Sometimes those atoms travel in groups called molecules. Whether a substance contains molecules or individual atoms, those tiny bits of matter are in constant motion.

The molecules in this container move and bounce off of one another. Thermal energy is the energy present in matter due to the motion of its particles. Thermal energy is a type of kinetic energy because the atoms or molecules in matter move.

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Thermal Energy

Recall that thermal energy comes from the movement of particles in matter. Temperature is the measure of the average kinetic energy of particles in a substance. Temperature is a quantitative way to describe thermal energy because it uses numbers.

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Temperature

Temperature Continued

You are probably most familiar with measuring temperature using degrees Fahrenheit (°F). When you watch the news or use your phone to look up the weather, the temperatures reported are in Fahrenheit.

However, scientists usually use degrees Celsius (°C) to measure temperature. The Celsius temperature scale is based on the properties of water.

• Water freezes at 0°C.

• Water boils at 100°C.

Using the boiling and freezing points of water provides useful reference points on the Celsius scale.


Temperature measures the average kinetic energy of particles in matter. Scientists measure temperature using degrees Celsius.

​You have probably seen a thermometer like this before.

What is the red stuff inside of the thermometer?

Why does it rise and fall with temperature fluctuations?

The temperature of a substance is related to the kinetic energy of its molecules. Examine the GIF below. Note the relative kinetic energy of the molecules at a low temperature. Then note the kinetic energy of the molecules at a high temperature.

How do the molecules behave differently in different temperatures?

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Relationship Between Temperature and Kinetic Energy

​Think about it in human terms... how would you feel if you were in each of these places?

​When you think about thermal energy, you might confuse thermal energy, temperature, and heat. All three words are very similar concepts. As you view the video pay attention to the difference between thermal energy, heat, and temperature.

​Although the three terms are similar, heat, temperature, and thermal energy have distinct meanings.

• Thermal energy refers to the kinetic energy of all of the particles of a substance.

• Temperature refers to the average kinetic energy of the particles in a substance.

• Heat refers to the transfer of thermal energy.

Two substances with the same temperature can have different amounts of thermal energy if one has a greater mass. You will learn more about how mass relates to thermal energy in an upcoming lesson.

​Science Fun Fact

​What animal sees in the way this image to the right is depicted?

Hint: This animal is able to see thermal energy to pick out it's targets.

​HAVE AN AMAZING WEEKEND!