temperature and heat

example of thermal energy transfer

Figure 18.3 illustrates an example of thermal energy transfer. Before the spoon was put into the steaming hot coffee, it was cool to the touch. Once in the coffee, the spoon heated up quickly. The fast-moving particles of the coffee transferred some of their energy to the slower-moving particles of the spoon. The spoon particles started moving faster and became warmer, causing the temperature of the spoon to rise. Because the coffee particles lost some of their kinetic energy to the spoon particles, the coffee particles started to move more slowly. This caused the temperature of the coffee to fall. Before long, the coffee and spoon had the same temperature.

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heat

Something that has a high temperature is said to be hot. Does temperature measure heat? Is heat just another word for thermal energy? The answer to both questions is no. Heat is the transfer of thermal energy between objects that have different temperatures. Thermal energy always moves from an object with a higher temperature to an object with a lower temperature. When thermal energy is transferred in this way, the warm object becomes cooler and the cool object becomes warmer. Sooner or later, both objects will have the same temperature. Only then does the transfer of thermal energy end. For a visual explanation of these concepts, watch the animation "Temperature vs. Heat" at this URL: .

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kqed bridge thermometer

The roadway across the Golden Gate Bridge rises and falls as much as 16 feet depending on the temperature. When the sun hits the bridge, the metal expands and the bridge cables stretch. As the fog rolls in, the cables contract and the bridge goes up. Curators from the Outdoor Exploratorium in San Francisco have set up a scope two miles away so you can see how the bridge is moving up or down depending on the weather. For more information on how the bridge moves due to temperature, see http://science.kqed.org/quest/video/quest-lab-bridge-thermometer/ . Heat is the transfer of thermal energy between objects that have different temperatures. Thermal energy always moves from an object with a higher temperature to an object with a lower temperature. Specific heat is the amount of energy (in joules) needed to raise the temperature of 1 gram of a substance by 1C. Substances differ in their specific heat.

specific heat

The girls in Figure 18.4 are having fun at the beach. Its a warm, sunny day, and the sand feels hot under their bare hands and feet. The water, in contrast, feels much cooler. Why does the sand get so hot while the water does not? The answer has to do with specific heat. Specific heat is the amount of energy (in joules) needed to raise the temperature of 1 gram of a substance by 1C. Specific heat is a property that is specific to a given type of matter. Table 18.1 lists the specific heat of four different substances. Metals such as iron have relatively low specific heat. It doesnt take much energy to raise their temperature. Thats why a metal spoon heats up quickly when placed in hot coffee. Sand also has a relatively low specific heat, whereas water has a very high specific heat. It takes a lot more energy to increase the temperature of water than sand. This explains why the sand on a beach gets hot while the water stays cool. Differences in the specific heat of water and land also affect climate. To learn how, watch the video at this URL: MEDIA Click image to the left or use the URL below. URL: In Table 18.1, how much greater is the specific heat of water than sand? Substances iron sand wood water Specific Heat (joules) 0.45 0.67 1.76 4.18

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temperature

No doubt you already have a good idea of what temperature is. You might define it as how hot or cold something feels. In physics, temperature is defined as the average kinetic energy of the particles in an object. When particles move more quickly, temperature is higher and an object feels warmer. When particles move more slowly, temperature is lower and an object feels cooler.

measuring temperature

Temperature is measured with a thermometer. A thermometer shows how hot or cold something is relative to two reference temperatures, usually the freezing and boiling points of water. Scientists often use the Celsius scale for temperature. On this scale, the freezing point of water is 0C and the boiling point is 100C. To learn more about measuring temperature, watch the animation Measuring Temperature at this URL: Did you ever wonder how a thermometer works? Look at the thermometer in Figure 18.2. Particles of the red liquid have greater energy when they are warmer, so they move more and spread apart. This causes the liquid to expand and rise higher in the glass tube. Like the liquid in a thermometer, most types of matter expand to some degree when they get warmer. Gases usually expand the most when heated, followed by liquids. Solids generally expand the least. (Water is an exception; it takes up more space as a solid than as a liquid.)

temperature and thermal energy

If two objects have the same mass, the object with the higher temperature has greater thermal energy. Temperature affects thermal energy, but temperature isnt the same thing as thermal energy. Thats because an objects mass also affects its thermal energy. The examples in Figure 18.1 make this clear. In the figure, the particles of cocoa are moving faster than the particles of bathwater. Therefore, the cocoa has a higher temperature. However, the bath water has more thermal energy because there is so much more of it. It has many more moving particles. Bill Nye the Science Guy cleverly discusses these concepts at this URL: MEDIA Click image to the left or use the URL below. URL: If youre still not clear about the relationship between temperature and thermal energy, watch the animation "Tem- perature" at this URL: .

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instructional diagrams

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questions

device for measuring temperature

a. thermal energy

b. heat

c. temperature

-->  d. thermometer

e. mass

f. Celsius

g. specific heat

What happens to water when you heat it?

a. The particles of the water gain kinetic energy.

b. The thermal energy of the water increases.

c. The temperature of the water rises.

-->  d. all of the above

total kinetic energy of particles of matter

-->  a. thermal energy

b. heat

c. temperature

d. thermometer

e. mass

f. Celsius

g. specific heat

What causes the liquid in a thermometer to rise?

-->  a. The liquid expands.

b. The liquid turns to a gas.

c. The liquid increases in mass.

d. The liquid has greater specific heat.

amount of energy needed to raise the temperature of 1 gram of a substance by 1 C

a. thermal energy

b. heat

c. temperature

d. thermometer

e. mass

f. Celsius

-->  g. specific heat

When heat is transferred between objects of different temperatures, what is the end result?

a. Both objects have a higher temperature.

b. Both objects have a lower temperature.

-->  c. Both objects have the same temperature.

d. The difference in temperature is greater.

Why does the sand on a beach get so much warmer than the water on a sunny day?

a. The particles of sand are smaller.

b. The sand has higher specific heat.

c. The water has less thermal energy.

-->  d. The water has greater specific heat.

average kinetic energy of particles of matter

a. thermal energy

b. heat

-->  c. temperature

d. thermometer

e. mass

f. Celsius

g. specific heat

scale for measuring temperature

a. thermal energy

b. heat

c. temperature

d. thermometer

e. mass

-->  f. Celsius

g. specific heat

Specific heat is measured in

a. grams.

b. degrees.

-->  c. joules.

d. newtons.

transfer of thermal energy between objects with different temperatures

a. thermal energy

-->  b. heat

c. temperature

d. thermometer

e. mass

f. Celsius

g. specific heat

measure that affects the thermal energy of matter but not its temperature

a. thermal energy

b. heat

c. temperature

d. thermometer

-->  e. mass

f. Celsius

g. specific heat

The particles of all matter are in constant random motion.

-->  a. true

b. false

Objects with the same temperature always have the same total kinetic energy.

a. true

-->  b. false

A thermometer measures temperature relative to two reference temperatures.

-->  a. true

b. false

Heat is always transferred from a larger object to a smaller object.

a. true

-->  b. false

Differences in the specific heat of land and water affect climate.

-->  a. true

b. false

Only warm or hot objects have thermal energy.

a. true

-->  b. false

If particles of an object start to move more quickly, the objects temperature rises.

-->  a. true

b. false

Temperature is the same thing as thermal energy.

a. true

-->  b. false

An object with a higher temperature always has greater thermal energy than an object with a lower

a. true

-->  b. false

On the Celsius scale, the boiling point of water is 32 C.

a. true

-->  b. false

Most types of matter expand to some degree when they get warmer.

-->  a. true

b. false

Temperature is a physical property of matter.

a. true

-->  b. false

Thermal energy always moves from an object with a higher temperature to an object with a lower

-->  a. true

b. false

Specific heat is a property that is specific to a given type of matter.

-->  a. true

b. false

Most metals have a very high specific heat.

a. true

-->  b. false

If two objects have the same mass, the object with the higher temperature always

a. has greater thermal energy.

b. has higher specific heat.

c. feels warmer.

-->  d. two of the above

Which of the following statements about temperature is true?

a. Temperature measures heat.

-->  b. Temperature measures kinetic energy.

c. Temperature is the same thing as heat.

d. Temperature is the same thing as thermal energy.

If a bucket full of water and a cup full of water have the same temperature, then the water in the

a. bucket and cup have the same thermal energy.

-->  b. bucket has greater thermal energy.

c. cup has lower average kinetic energy.

d. cup has lower specific heat.

The thermal energy of an object depends on its

a. mass.

b. temperature.

c. specific heat.

-->  d. two of the above

If you put a cool spoon into a cup of hot coffee, the temperature of the spoon rises because

a. thermal energy is transferred from the coffee to the spoon.

b. specific heat is transferred from the coffee to the spoon.

c. particles of the spoon gain kinetic energy.

-->  d. two of the above

Which of the following materials has the greatest specific heat?

a. iron

b. sand

c. wood

-->  d. water

A material with greater specific heat

a. warms up more quickly.

b. requires less energy to get hot.

c. always has a higher temperature.

-->  d. none of the above

diagram questions

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