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Energy and Diet: Defining a Calorie

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Activity Overview: While British thermal units (Btus) and kilowatt-hours (kWh) are common units of energy in the energy industry, the unit of energy most common in everyday life is the calorie. Your students may see the number of calories on their food packaging or in dietary recommendations from the Food and Drug Administration (FDA). However, what is commonly referred to as the calorie is actually the kilocalorie (kcal or Cal), which is defined as the amount of energy (as heat) it will take to raise the temperature of 1 kilogram (kg) of water by 1 degree Celsius at standard pressure (air pressure at sea level).

This activity uses the small calorie or gram calorie (cal), which is defined as the amount of heat required to raise the temperature of 1 gram (g) of water by 1 degree Celsius.

Procedure:

Visualize the energy of the calorie by mapping it onto the concept of a melting ice cube. Measure the mass of an ice cube from the cafeteria or a freezer tray. How many grams is it?

The investigation depends on the following premises, which you can share with the class.

  • As soon as the ice cube leaves a 0° environment, such as the freezer, it is absorbing energy from the warmer environment around it.
  • The number of degrees Celsius required to melt this ice cube is 1°.

Based on the mass in grams of the ice cube, how many calories has the water absorbed from its warmer environment?

The number of gram calories required is equal to the mass of the ice cube.

Exposing the ice cube to increased heat via sunlight, flame, or an electric burner will result in melting faster as the ice cube absorbs energy faster.

TEKS

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