# Making Heat

How do you make heat? You could burn things (chemical reactions), or you could rub things together (friction). When you burn things, thermal energy is released. Thermal energy is measured in calories. For example, when you burn wood, you release 3000 calories for each gram of wood. When you burn an apple, it creates only 600 calories. The amount of energy released is directly related to the chemical bonds that are broken and formed. If you use that idea, there is more energy available when you break and rebond the atoms in wood, than when you do the same to an apple.

# Losing Energy

We just talked about friction. Heat is also created because of inefficiency. When a car engine runs, a lot of heat is given off. Much of that heat is the result of the friction and inefficiency in the running motor. When you lift something and your muscle contracts, you are only 25% efficient. Seventy-five percent of the energy is lost to heat.

# More Transfer of Energy

Heat is the thermal energy transported from one system to another because of a temperature difference. The transfer of that energy stops when the temperature balances out in the entire environment. Scientists use the unit of a calorie to measure heat. You might be saying, "I've heard of calories. Are those like the ones in food?" The answer is "Yes." One calorie is measured as the amount of energy needed to raise the temperature of one gram of water, one degree Celsius. When you “burn” food (this happens VERY slowly in your body), you release energy.

# Specific Heat Capacity

There is also something totally important called specific heat capacity. It is the amount of energy required to raise the temperature of one gram of a substance by one degree Celsius. The specific heat capacity for water is one. As we said, heat is a form of thermal energy. Because it's energy, scientists also use the units of Joules to measure the energy. One calorie equals 4.186 Joules which also equals 4.186 Watts seconds (Ws). Does that mean you can measure the amount of energy you make in your body in one second and express that in terms of an electric value (Watts)? Yes, the rate at which energy is created or used in your body can be expressed as electrical power.

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LaunchPad: The Heat is On! (NASA-eClips Video)

Physics4Kids: Temperatures
Chem4Kids: Reaction Thermodynamics
Chem4Kids: Changing States of Matter
Chem4Kids: Catalysts
Biology4Kids: System Regulation
Biology4Kids: Endocrine System
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