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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. For a visual introduction to these concepts, watch the animation “Temperature vs. Heat” at this URL:

http://www.sciencehelpdesk.com/unit/science2/3

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 warmer to cooler substances until both substances have the same temperature.

Vocabulary

  • heat : Transfer of thermal energy between objects that have different temperatures.

Practice

View the slides at the following URL, and then do the matching questions below.

http://www.slideshare.net/AlkorBilingual/u11-heat-temperature

Fill in the blank before each number with the letter of the term that is the best match. Note that there are more terms than needed.

_____ 1. amount of heat in a system

_____ 2. increase in volume that occurs when a system gains thermal energy

_____ 3. state of matter that expands most when it is heated

_____ 4. unit used to measure heat

_____ 5. amount of thermal energy that is transferred from one system to another

_____ 6. instrument used to measure temperature

a. contraction

b. heat

c. solid

d. expansion

e. temperature

f. heat meter

g. gas

h. joule

i. degree

j. thermometer

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.

Vocabulary

heat

heat

Transfer of thermal energy between objects that have different temperatures.

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