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43

of energy tells us that the work done plus the heat energy produced must equal

the original amount of energy available.

total energy = work done + heat produced (usually by friction)

E

t

= W + H

3

Notice that as energy, heat has the unit of joule (J). This is known as the

mechanical equivalent of heat. A traditional unit for measuring heat energy is

the calorie. A calorie (cal) is defined as the amount of heat necessary to raise

one gram of pure liquid water by one degree Celsius (from 14.5° to 15.5° C) at

normal atmospheric pressure. In terms of the SI energy unit, 1 cal = 4.186 J. A

kilocalorie is the amount of heat necessary to raise the temperature of one

kilogram of water one degree Celsius. The calorie that we have defined is not

the same as the one used when discussing diets and nutrition. A diet calorie

(Cal) is equal to one kilocalorie and is commonly written with a capital C to

avoid confusion. We sometimes refer to a “big” calorie and a “little” calorie.

1 food Calorie = 1000calorie

1 food Calorie = 4186 joules

4

When heat is added to a substance the temperature increases. But how

much does the temperature rise? That depends. If you add equal amounts of heat

to equal masses of iron and aluminum, you might be surprised to find that their

temperatures changes are different. If the temperature of the iron increased by

100° C, the corresponding temperature change in the aluminum would be only

48° C. You would have to add more than twice the amount of heat to the

aluminum to get the same temperature change as for an equal mass of iron. This

result reflects the fact that the internal forces of the materials are different. We

express this difference in terms of specific heat. The specific heat of a substance

is the amount of heat, necessary to raise the temperature of one kilogram of a

substance one degree Celsius.

5

Water’s specific heat is 1.0 kcal / kg ⋅°C because one kilocalorie is the

amount of heat that raises the temperature of one kilogram of water one degree

Celsius. Other substances require different amounts of heat to raise the

temperature of one kilogram of the substance by one degree. Notice that the

units of specific heat are kcal / kg ⋅°C (amount of heat per unit mass per degree

change in temperature). The SI units or J / kg ⋅°C. The greater the specific heat

of a substance, the greater is the amount of heat required to raise the temperature

of a unit mass. Put another way, the greater the specific heat, the greater is its

43 of energy tells us that the work done plus the heat energy produced must equal the original amount of energy available. total energy = work done + heat produced (usually by friction) Et = W + H 3 Notice that as energy, heat has the unit of joule (J). This is known as the mechanical equivalent of heat. A traditional unit for measuring heat energy is the calorie. A calorie (cal) is defined as the amount of heat necessary to raise one gram of pure liquid water by one degree Celsius (from 14.5° to 15.5° C) at normal atmospheric pressure. In terms of the SI energy unit, 1 cal = 4.186 J. A kilocalorie is the amount of heat necessary to raise the temperature of one kilogram of water one degree Celsius. The calorie that we have defined is not the same as the one used when discussing diets and nutrition. A diet calorie (Cal) is equal to one kilocalorie and is commonly written with a capital C to avoid confusion. We sometimes refer to a “big” calorie and a “little” calorie. 1 food Calorie = 1000calorie 1 food Calorie = 4186 joules 4 When heat is added to a substance the temperature increases. But how much does the temperature rise? That depends. If you add equal amounts of heat to equal masses of iron and aluminum, you might be surprised to find that their temperatures changes are different. If the temperature of the iron increased by 100° C, the corresponding temperature change in the aluminum would be only 48° C. You would have to add more than twice the amount of heat to the aluminum to get the same temperature change as for an equal mass of iron. This result reflects the fact that the internal forces of the materials are different. We express this difference in terms of specific heat. The specific heat of a substance is the amount of heat, necessary to raise the temperature of one kilogram of a substance one degree Celsius. 5 Water’s specific heat is 1.0 kcal / kg ⋅°C because one kilocalorie is the amount of heat that raises the temperature of one kilogram of water one degree Celsius. Other substances require different amounts of heat to raise the temperature of one kilogram of the substance by one degree. Notice that the units of specific heat are kcal / kg ⋅°C (amount of heat per unit mass per degree change in temperature). The SI units or J / kg ⋅°C. The greater the specific heat of a substance, the greater is the amount of heat required to raise the temperature of a unit mass. Put another way, the greater the specific heat, the greater is its

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