Download Heat Transfer and more Summaries Heat and Mass Transfer in PDF only on Docsity!
Heat Transfer
Reading Preview^ ~ab^ Discover Activity
Key Concepts
- How is temperature measured?
- In what three ways is heat transferred?
- How is heat transferred in the troposphere? Key Terms
- temperature
- thermal energy
- thermometer
- heat
- conduction
- convection
- convection currents
'-@ Target Reading Skill
Outlining As you read, make an outline about how heat is transferred. Use the red headings for the main topics and the blue headings for the subtopics.
Heat Transfer I. Thermal energy and temperature A. Measuring temperature B. II. How heat is transferred A.
.zone
What Happens When Air Is Heated?
- Use heavy scissors to cut the flat part out of an aluminum pie plate. Use the tip of the scissors to poke a small hole in the middle of the flat part of the plate.
- Cut the part into a spiral shape, as shown in the photo. Tie a 30-centimeter piece of thread to the middle of the spiral.
- Hold the spiral over a source of heat, such as a candle, hot plate, or incandescent light bulb. Think It Over Inferring What happened to the spiral? Why do you think this happened?
You pour a cup of steaming tea from a teapot. Your teacup is warm to the touch. Somehow, heat was transferred from one object (the cup) to another (your hand) that it was touching. This is an example of conduction, one of three ways that heat can be transferred. As you'll learn in this section, heat transfer in the troposphere plays an important role in influencing Earth's weather.
It takes only a smaU amount of energy to heat up a cup of tea.
42 • I
Thermal Energy and Temperature
The tea in the cup and in the teapot are at the same temperature but have a different amount of total energy. To understand this, you need to know that all substances are made up of tiny parti cles that are constantly moving. The faster the particles are mov ing, the more energy they have. Figure 4 shows how the motion of the particles is related to the amount of energy they hold.
Temperature is the average amount of energy of motion of each
particle of a substance. That is, temperature is a measure of how hot or cold a substance is. In contrast, the total energy of motion in the particles of a substance is called thermal energy. The hot tea in the teapot has more thermal energy than the hot tea in the cup because it has more particles.
Measuring Temperature Temperature is one of the most important factors affecting the weather. Air temperature is usually measured with a thermometer. A thermometer is a thin glass tube with a bulb on one end that contains a liquid, usually mercury or colored alcohol. Thermometers work because liquids expand when they are heated and contract when they are cooled. When the air tem perature increases, the temperature of the liquid in the bulb also increases. This causes the liquid to expand and rise up the column.
Temperature Scales Temperature is measured in units called degrees. Two temperature scales are commonly used: the Celsius scale and the Fahrenheit scale. Scientists use the Celsius scale. On the Celsius scale, the freezing point of pure water is O°C (read "zero degrees Celsius"). The boiling point of pure water at sea level is 100°e. Weather reports in the United States use the Fahrenheit scale. On the Fahrenheit scale, the freezing point of water is 32°F and the boiling point is 212°F. Reading (^) Which temperature scale do scientists use? Checkpoint
FIGURE 4 Movement of Molecules The iced tea is cold, so its molecules move slowly. The herbal tea is hot. so its molecules move faster than the molecules in the iced tea. Inferring Which liquid has a higher temperature?
Converting Units
Temperatures in weather reports use the Fahrenheit sca'le, but scientists use the Celsius scale. Temperature readings can be converted from the Fahrenheit scale to the Celsius scale using the following equation: °C = ~ (OF - 32) 9 If the temperature is 68°F, what is the temperature in degrees Celsius? °C =.2 (68 - 32) 9 °C = 20°C Practice Problem Use the equation to convert the following temperatures from Fahrenheit to Celsius: 35.0°F, 60.0°F, and 72.0°F.
Chapter 2 I. 43
Heat transfer by radiation
FIGURE 5 Heat Transfer All three types of heat transfer radiation, conduction, and convection-help to warm the troposphere. Radiation Conduction^ Convection
Section 2 Assessment
'!) Target Reading Skill Outlining Use the information in your outline about heat transfer to help you answer the questions below. Reviewing Key Concepts
- a. Defining What is temperature? b. Identifying What instrument is used to measure air temperature? c. Comparing and Contrasting A pail of water is the same temperature as a lake. Compare the amount of thermal energy of the water in the lake and the water in the pail.
- a. Naming Name three ways that heat can be transferred. b. Describing How do the three types of heat transfer work together to heat the troposphere?
c. Identifying What is the major way that heat is transferred in the troposphere? d. Applying Concepts Explain how a hawk or eagle can sometimes soar upward without flapping its wings.
- Converting Units Use the equation from the Math Skills Activity to convert the following temperatures from Fahrenheit to Celsius: 52°F, 86°F, 77°F, and 97°F.
Chapter 2 I • 45
