Heat and Temperature
Reading: Textbook Chapter 14 p.470-493
What is Heat?
Heat is the thermal energy of the particles in a substance due to the kinetic energy of the particles moving. Look at the cool images of thermal energy, heat, at the What is Heat? web site.
Temperature is the measure of how hot or cold something is; specifically, a measure of the average kinetic energy of the particles in an object. When we touch an object, such as the hood of an automobile, we are getting a rough sense of the temperature of the object. The particles in an object is constantly moving. Each moving particle as kinetic energy. The more the particle moves the more kinetic energy it has. Therefore, as the kinetic energy increases the temperature increases.
A Thermometer is an instrument that measures and indicates the temperature. Common thermometers rely on expansion. A liquid thermometer uses the expansion of a liquid, alcohol or mercury, to indicate changes in temperature.
Thermometers can use different methods. Liquid thermometers can measure only temperature within a certain range. A refrigerator thermometer is based on the expansion of metal. A digital thermometer is designed to measure temperature changes by noting change in electric current.
Fahrenheit and Celsius are common scales used for measuring temperature. The degrees on the Fahrenheit scale are called degrees Fahrenheit or F°, water freezes at 32°F and boils at 212°F.
The United States is about the only country that used the Fahrenheit scale, other countries use the Celsius scale. The Celsius scale give a value of 0°C to the freezing point of water and a value of 100°C to the boiling of water.
To convert one scale to the other, use one of the following formulas.
Fahrenheit temperature = (1.8 X Celsius temperature) + 32
F= 1.8C + 32
Celsius temperature = Fahrenheit temperature - 32/ 1.8
C= F-32 / 1.8
The Kelvin scale is based on absolute zero. Absolute zero is the lowest temperature possible, the temperature at which molecular energy or movement of particles is 0. This temperature is 0 on the Kelvin scale and -273.16°C.
Kelvin temperature = Celsius temperature + 273
K = C + 273
Relating Temperature to Energy Transfer
The feeling associated with temperature differences results from energy transfer. For example, when you hold an ice cube, the molecules in the ice are moving slower than the molecules in your hand. The faster moving molecules of your hand transfer energy to the slower moving molecules in the ice causing those molecules to speed up and their kinetic energy to increase. This causes the ice to melt.
Temperature changes indicate an energy transfer. Heat is the energy transferred between objects that are at different temperatures. The transfer of energy always takes place from a substance of higher temperature to lower temperature. You can use temperature to predict which way energy transfer is occurring.
Complete the learning activity Work and Power.
Go to assignments and do questions 1-5.
Methods of Energy Transfer
1. Conduction is the transfer of energy as heat through a material. Conduction takes place when two objects that are in contact are at unequal temperatures.
2. Convection is the movement of matter due to differences in density that are caused by temperature variations. Convection results from the movement of warm fluids, including air. The heated fluid expands and rises about the cooler fluid. Heated fluids have convection currents. Convection currents are the vertical movement of air currents due to temperature variations.
3. Radiation is the energy that is transferred as electromagnetic waves, such as visible light and infrared waves. Radiation does not require physical contact between objects. Radiation differs from conduction and convection in that it does not involve the movement of matter. Radiation is the only method of energy transfer that can take place in a vacuum, such as outer space. Much of the energy we receive from the sun is transferred by radiation.
Heat transfer type shown using thermal imaging can be seen at Cool Cosmos Heat & Temperature.
Go to assignments and do questions 6-9.
Conductors and Insulators
Any material through which energy can be easily transferred as heat is called a conductor. For example, pans must be able to conduct energy for cooking.
Insulators are materials that do not easily transfer energy. For example, materials used for the roof and walls of buildings are made of material that do not easily transfer energy. Energy is transferred by the collision of particles.
Specific heat describes how much energy is required to raise an object's temperature. Specific heat can be used in calculations to predict the effects of larger temperature changes for masses other than 1kg. The following formula is used when predicting energy used.
energy = (specific heat) x (mass) x (temperature change)
Go to assignments and do questions 10-16.
Work can increase the average kinetic energy. Some of the energy from food is transferred as heat to blood moving throughout the human body. Your body is a heating system that is able to maintain a temperature of 98.6°F. If you are surrounded by cold air , energy will be transferred from your skin to the air. To compensate, stored nutrients are broken down by your body to provide the energy to your blood that is being transferred to the air.
Heated water or air transfers energy as heat in central heating systems. Solar heating systems also use air or water.
Usable energy decreases in all energy transfers. Insulation minimizes undesirable energy transfer.
Cooling systems often use evaporation to transfer energy from their surroundings. Hidden in the back of a refrigerator is a set of coiled pipes through which a substance called a refrigerant flows. The refrigerant evaporates into a gas then condenses back to a liquid during each cooling cycle. Condensation transfers energy to the surroundings. Heat pumps can transfer energy to or from rooms.
Heat engines convert potential chemical energy and internal kinetic energy to mechanical energy by using the process of combustion. Internal combustion engines burn fuel inside the engine. Not all internal combustion engines work alike. Diesel engines use internal combustion , but have no spark plug instead they use fuel-air mixture compressed until it becomes hot enough to ignite. Internal combustion engines vary in number of pistons.
Go to assignments and do question 17- 21.
1. Do practice problems on p.477 in the Physical Science textbook.
2. Search the Internet for a temperature unit converter. Convert the following temperatures.
a) 45 C to F b) 125 C to F c) 150 C to K d) 0 F to C e) 50 F to C f) 110 F to K g) -25 F to C h) 23K to C i) 400K to C j) 650 K to F
3. Two cups contain the same amount of water.
a) What device would be best for comparing the average energy of the particles of each sample of water?
b) Explain how this device would help you compare the energies of the particles.
4. Define absolute zero
in terms of kinetic energy of particles.
5. Determine which of the following has a higher temperature and which contains a larger amount of total kinetic energy: a cup of boiling water or Lake Michigan.
6. Predict whether the hottest part of a room will be near the ceiling, in the center, or near the floor; given that there is a hot-air vent hear the floor. Explain your reasoning.
7. Explain why cookies baked near the turned-up edges of a cookie sheet receive more energy than those baked near the center.
8. A couple decide to camp on the beach after a beautiful day enjoying the sun. After dark, they find the sand is cold to their feet and have to put on shoes. When they wake up in the middle of the night, they find that they are very cold and there is a cold wind blowing outside. What types of energy transfer would explain the changes from the day to the night at the beach? Explain each.
9. Identify the types of heat transfer shown in the picture above. Give the type of heat transfer and a description of where it is in the picture.
10. The sun goes down, snow falls on cement playground and on an asphalt road. Why does the snow on the road melt sooner than on the cement?
. Why are fireplace pokers made of iron and not copper?
12. Some animals have hair which is composed of solid tubular strands, while others have hollow, air-filled tubes. Where would one more likely find the latter animal: In cold climates, or warm? Explain why.
13. Two identical cups of cocoa are sitting on a table. One has a metal spoon in it and one does not. After five minutes, which cup is cooler?
. In Alaska, a lack of snow allowed the ground to freeze down to a depth of about one meter, causing buried water pipes to freeze and burst. Why did a lack of snow lead to this situation?
15. Several days after the end of a snowstorm, the roof of a house is completely covered with snow, another house's roof has no snow. Which house is probably better insulated? Why?
16. Do practice problems on p.486 in the Physical Science textbook.
17. List one type of home heating system, and describe how it transfers energy to warm the air inside the house.
18. Write at least five sentences comparing the advantages and disadvantages of using a solar heating system in Kirksville.
19. Water has a high specific heat, meaning it takes a good deal of energy to raise its temperature. For this reason, the cost of heating water may be a large part of a monthly energy bill. Describe two ways the people in your household could change their routines, without sacrificing results, in order to save money and energy by using less hot water.
20. Draw and describe each of the strokes of an automobile engine. Explain how the spark-plug ignition of compressed gas results in work done by the engine.
21. Take the Heat Review Quiz and show the teacher your results.
Chapter 14 test