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# Heat

## Explores how thermal energy moves between substances.

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Heat

This chef is taking corn bread out of a hot oven. What happened to the batter when it was put in the oven? Did the hot oven add “heat energy” to the batter? Not exactly. Contrary to popular belief, heat is not a form of energy.

### What Is Heat?

Heat is the transfer of thermal energy between substances. Thermal energy is the kinetic energy of moving particles of matter, measured by their temperature. Thermal energy always moves from matter with greater thermal energy to matter with less thermal energy, so it moves from warmer to cooler substances. You can see this in the Figure below. Faster-moving particles of the warmer substance bump into and transfer some of their energy to slower-moving particles of the cooler substance. Thermal energy is transferred in this way until both substances have the same thermal energy and temperature

Q: How is thermal energy transferred in an oven?

A: Thermal energy of the hot oven is transferred to the cooler food, raising its temperature.

### Cooling Down by Heating Up

How do you cool down a glass of room-temperature cola? You probably add ice cubes to it, as in the Figure below. You might think that the ice cools down the cola, but in fact, it works the other way around. The warm cola heats up the ice. Thermal energy from the warm cola is transferred to the much colder ice, causing it to melt. The cola loses thermal energy in the process, so its temperature falls.

### Summary

• Heat is the transfer of thermal energy between substances. Thermal energy is the kinetic energy of moving particles of matter, measured by their temperature.
• Thermal energy always moves from warmer to cooler substances until both substances have the same temperature.

### Review

1. Define heat.
2. Describe how thermal energy is transferred.
3. Hot cocoa is poured into a cold mug. Apply the concept of heat to explain what happens next.

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### Vocabulary Language: English

heat

Transfer of thermal energy between objects that have different temperatures.