Chapter 22: Heat Transfer

Convection

A means of heat transfer by movement of the heated substance itself, such as by currents in a fluid. Convection occurs in all fluids, whether liquids or gas, When fluid is heated, it expands, becomes less dense, and rises

Absorption and reflection are opposite processes...

Absorption and reflection are opposite processes. Therefore, a good absorber of radiant energy reflects very little radiant energy, including the range of radiant energy we call light. A good absorber appears dark. The pupil is black because it absorbs all the light

You can stick your hand into a hot pizza oven for several seconds without harm, whereas you'd never touch the metal inside surfaces for even a second. Why?

Air is a poor conductor, so the rate of heat flow from the hot air to your relatively cool hand is low. But touching the metal parts is a different story. Metal conducts heat very well, and a lot of heat in a short time is conducted into your hand when thermal contact is made.

All object continually emit what?

All object continually emit radiant energy in a mixture of wavelenths. Objects at low temperatures emit long waves, just as long, lazy waves produced when you shake a rope with little energy. Higher-temperature objects emit waves of shorter wavelenths. Objects of everyday temperatures emit waves mostly in the long-wavelenth end of the infrared region, which is betweeen radio and light waves. Shorter-wavelength infrared waves absorbed by out skin produces the sensation of heat

What happens at about 1200C?

At about 1200C all the different waves to which the eye is sensitive are emitted and we see and object as "white hot".

What do atmospheric gases do?

Atmospheric gases (mainly carbon dioxide and water vapor) absorb and re-emit much of this long-wavelength terrestrial radiation back to Earth. So the long-wavelenth radiation that cannot escape Earth's atmosphere warms Earth

How do birds vary their insulation

Birds vary their insulation by fluffing their feathers to create air spaces

How is the sun's heat transmitted through the atmosphere?

By radiation process

IF you hold one end of a metal bar against a piece of ice, the end in your hand will soon become cold. Does cold flow from the ice to your hand?

Cold does NOT flow from the ice to your hand. Heat flows from your hand to the ice. The metal is cold to your touch because you are transferring heat to the metal.

Why do cars get so hot in bright sunlight?

Compared with the car, the sun's temperature is very high. This means the waves it radiates are very short. These short waves easily pass through both Earth's atmosphere and the glass windows of the car. So, the sun's light gets into the car where it is then absorbed. These new long wavelength can't pass through windows, so the heat is trapped

What is conduction explained by?

Conduction is explained by collisions between atoms or molecules, and teh actions of loosely bound electrons

What produce winds

Convection currents stirring the atmosphere produce winds. Some parts of Earth's surface absorbs heat from the sun more readily than others. The uneven absorption causes uneven heating of the air near the surface, and creates convection currents. In the daytime, the shore warms more easily than the water. Air over the shore rises, and coooler air from above the water takes its place. The result is a sea breeze. At night, the process reverses as the shore cools off more quickly than the water- the warmer air is now over the sea. If you build a fire on the beach, you'll notice that the smoke sweeps inward in the day and seaward at night.

On a sunny day, ____ ______ is a net absorber.

Earth's surface

Terrestrial Radiation

Energy that Earth radiates

Conduction

Energy transfer from particle to particle within certain materials, or from one materials to another when the two are in direct contact

Wood is a better insulator than glass. Yet fiberglass is commonly used to insulate wooden buildings. Why?

Finberglass is a good insulator, many times better than glass, because of the air that is trapeed among its fibers

Good absorbers are also what? poor absorbers are also what

Good absorbers are also good emitters; poor absorbers are poor emitters

What is different about heat form coldness

Heat is energy and is tangible, cold is not. Cold is simply the absence of heat.

You can hold your fingers beside the candle flame without harm, but not above the flame. Why?

Heat travels UPWARD by air convection. Since air is a poor conductor, little heat travels sideways.

High-temperature objects radiate ____ ____; low temperature objects radiate ____ ____

High temperature objects radiate short waves; low temperature objects radiate long wavelenghts

What would happen if a good absorber were not also a good emitter?

If a good absorber were not also a good emitter, then black objects would remain warmer tthan light-colored objects and never come to thermal equilibrium with them, but object in thermal contact do come to thermal equilibrium with them. Each object is emitting as much energy as it is absorbing, so dark objects that absorb a lot must also emit a lot as well

If a good absorber of radiant energy were a poor emitter, how would its temperature compare with its surroundings?

If a good absorber were not also a good emitter, there would be a net absorption of radiant energy and the temperature of a good absorber woud remain higher than the temerperature of the surroundings. Things around us approach a common temperature only becasue good absorbers are, by their very nature, also good emitters

If a home becomes colder, what is that due to

If a home comes colder, it is because heat flows out

What happens if an object is hot enough?

If an object is hot enough, some of the radiant energy emits is in the range of visible light. At a temperature of 500C an objet begins to emit the longest waves we can see, red. Higher temperatures produce yellowish light

What happens if several object are near one another and have different temperatures?

If several objects near one another have different temperature, then those that are warm become cooler and those that are cool become warmer, until all have a common temperature. The equalization of temperatures is brought about in three ways: by conduction, by convection, and by radiation

Insulator

Material that delays the transfer of heat. A poof conductor is a good insulator!

What make good conductors?

Materials composed of atoms with loose outer electrons are good conductors of heat (and electricity, also). Because metals have the loosest outer electrons, they are the best conductors of heat and electricity

Is it more effiecient to paint a heating radiator black or silver?

Most of the heat provided by a heating radiator is accomplished by convection, so the color is not really that important for optimum efficiency, however, the radiators should be painted a dull black so the contribution by radiation is increased

No insulator can keep heat form getting THROUGH . An insulator just does what?

NO insulator can keep heat from getting through. An insulator just REDUCES the rate at which heat gets through.

SInce a hot cup of tea loses heat more rapidly than a lukewarm cup of tea, would it be correct to say that a hot cup of tea will cool to room temperature before lukewarm cup of tea will?

No! Although the rate of cooling is greater for the hotter cup, it has further to cool to reach thermal equilibrium. The extra time is equal to the time it takes to cool to the initial temperature of the lukewarm cup of tea. Cooling RATE and cooling TIME are not the same

Why do openings appear black?

Openings appear black because the radiant energy is that eneters is reflected from the inside walls many times

When do record breaking cold nights occur?

Record breaking cold nights occur when skies are clear

Describe rising warm air

Rising warm air, like a rising balloon, expands. Why? because less atmospheric pressure squeezed on it at higher altitudes. As the air expands, it cools, just the opposite of what happens when air is compressed. If you've ever compressed air with a tire pump, you probably noticed that the air and pump become quite hot. The opposite happens when air expands, Expanding air cools.

Are snowflakes good insulators? Why?

Snowflakes imprison a lot of air in their crystals and are good insulators. Snow slows the escape of heat from Earth's surface, shields skimo dewellings from the cold, and provides protection from the cold to animals on cold winter nights. Snow prevents any heat from escaping too rapidly

What are the good insulating properties of materials such as wool, fur, and feathers due to

The good insulating properties of materials such as wool, fur, and feathers are largely due to the air spaces they contain

What does the rate of cooling of an object depend on?

The rate of cooling of an object depends on how much hotter the object is than the surroundings

Newton's law of cooling

The rate of cooling of an object, whether by conduction, convection, or radiation, is proportional to the temperature difference between the object and its surroundings. (also holds true for heating)

When will the temperature change per minute of a hot pie be more?

The temperature chnage per minute of a hot pie will be more if the hot pie is put in a cold freezer than if put on the kitchen table. A warm house iwll lose heat to the cold outside at a greater rate when there is a large difference between the inside and outside temperatures.

Greenhouse Effect

The warming effect whose cause is that short-wavelength radiant energy from the sun can enter the atmosphere and be absobed by Earth more easily than the long-wavelength energy from Earth can leave.

What does whether a surface plays a role of the net emitter or net absorber depend on?

WHether a surface plays a role of net emitter or net absorber depends on whetehr its temperature is above or below the surroundings.

Why do we insulate our homes?

We don't insulate our homes to keep the cold out; we insulate them to keep the heat IN

You feel the sun's heat not because it's __, but because it's ___

YOu feel the sun's heat not because it's hot, but because it's big.

Why does Bea and my mood ring on the dresser field different temperatures yet they are in the same room?

You can touch Bea and then your metal mood ring on the dresser, but they both FEEL different temperatures , yet they're in the same room! They actually are the same temperature, but the ring FEELS cooler because it's better conductor. Bea, on the other hand, is a poor conductor. little heat moves out of your hand into Bea, so your hand does not detect you are touching something the same temperature. Wood, wool, straw, paper, cork, and styrofoam area ll poor heat conductors. They are called insulators.

radiant energy

any energy, including heat, that is transmitted by radiation. Radiant energy is in the form of electromagnetic waves. It includes radio waves, microwaves, infrared radiation, visible light, ultra violet radiation, x-rays, and gamma rays

What heats Earth?

burning fossil fuels heats Earth. Except where the source of energy is solar, wind, or water, increased energy consumption on Earth adds heat.

radiation

energy transmitted by electromagnetic waves

Light-colored objects reflect more light and ___ than dark-colored ones

heat

LIquids and gases, in general, are good ____. Air is also a good ____

insulator

conductors

materials that conduct heat well

What is the best conductor? Why?

metal. Free electrons that can drift through the metals are made to jostle and transfer energy by colliding with atoms and other free electrons within the rod that is being warmed