PHYSICS CHAPTER 16

Global warming

-Energy absorbed from the Sun -Part reradiated by Earth as longer-wavelength terrestrial radiation

Winds

-Result of uneven heating of the airnear the ground. -Absorption of Sun's energy occursmore readily on different parts of Earth's surface

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?

NO! B/C 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.

Greenhouse effect

Named for a similar temperature-raising effect in florists' greenhouses. --All things radiate at a frequency (and therefore wavelength) that depends on the temperature of the emitting object. --Transparency of things depends on the wavelength of radiation.

Sea breeze

The ground warms more than water in the daytime. Warm air close to the ground rises and is replaced by cooler air from above the water.

Radiation

Transfer of energy from the Sun through empty space

Conduction

Transfer of internal energy by electron and molecular collisions within a substance, especially a solid

Poor conductors

are insulators. -molecules with tightly held electrons in a substance vibrate in place and transfer energy slowly—these are good insulators (and poor conductors). --Example: Glass, wool, wood, paper, cork, plastic foam, air --Substances that trap air are good insulators. Example: Wool, fur, feathers, and snow

The "greenhouse gases" that contribute to global warming absorb

more infrared radiation than visible.

Which is the better statement?

B. An object that absorbs energy well is black. This is a cause-and-effect question. The color black doesn't draw in and absorb energy. It's the other way around—any object that does draw in and absorb energy, will, by consequence, be black in color.

Although warm air rises, why are mountaintops cold and snow covered, while the valleys below are relatively warm and green?

BOTH, WARM AIR COOLS WHEN RISING & THERE IS A THICK INSULATING BLANKET OF AIR ABOVE VALLEYS. EARTH'S ATMOSPHERE ACTS A BLANKET WHICH KEEPS THE VALLEYS FROM FREEZING AT NIGHT TIME.

A hot pizza placed in the snow is a net

Net energy flow GOES FROM HIGHER TO LOWER temperature. Since the pizza is hotter than the snow, emission is greater than absorption, so it's a net emitter

Reflection of radiant energy

Opposite to absorption of radiant energy Any surface that reflects very little or no radiant energy looks dark Examples of dark objects: eye pupils, open ends of pipes in a stack, open doorways or windows of distant houses in the daytime. -Darkness often due to reflection of light back and forth many times partially absorbing with each reflection. -GOOD REFLECTORS ARE POOR ABSORBERS.

Cooling by expansion

Opposite to the warming that occurs when air is compressed.

The surface of Earth loses energy to outer space due mostly to

Radiation, is the only choice, given the vacuum of outer space.

Which body glows with electromagnetic waves?

SUN & EARTH. Earth glows in long-wavelength radiation, while the Sun glows in shorter waves.

It is commonly thought that a can of beverage will cool faster in the coldest part of a refrigerator. Knowledge of Newton's law of cooling

SUPPORTS THIS KNOWLEDGE. When placed in the coldest part of the refrigerator, the ΔT (i.e., the difference in temperature between the can and its surroundings) will be the largest, so it will cool the fastest.

Newton's law of cooling

-Approximately proportional to the temperature difference, ΔT, between the object and its surroundings -In short: rate of cooling ~ ΔT -Example: -Hot apple pie cools more each minute in a freezer than if left on the kitchen table. -Warmer house leaks more internal energy to the outside than a house that is less warm.Applies to rate of warming --Object cooler than its surroundings warms up at a rate proportional to ΔT. --Example: Frozen food will warm faster in a warm room than in a cold room.

Insulation

-Doesn't prevent the flow of internal energy -Slows the rate at which internal energy flows --Example: Rock wool or fiberglass between walls slows the transfer of internal energy from a warm house to a cool exterior in winter, and the reverse in summer. EX: Walking barefoot without burning feet on red-hot coals is due to poor conduction between coals and feet.

Conductors

-Good conductors conduct heat quickly. --Substances with loosely held electrons transfer energy quickly to other electrons throughout the solid. ---Example: Silver, copper, and other solid metals

Absorption of radiant energy

-Occurs along with emission of radiant energy -Good absorbers are good emitters -Poor absorbers are poor emitters ----Example: Radio dish antenna that is a good emitter is also a good receiver (by design, a poor transmitter is a poor absorber).

Wavelength of radiation

-Related to frequency of vibration (rate of vibration of a wave source) -Low-frequency vibration produces long-wavelength waves. -High-frequency vibration produces short-wavelength waves.

Convection

-Transfer of heat involving only bulk motion of fluids --Example: -Visible shimmer of air above a hot stove or above asphalt on a hot day -Visible shimmers in water due to temperature difference

Radiant energy

-Transferred energy -Exists as electromagnetic waves ranging from long (radio waves) to short wavelengths (X-rays) -In visible region, ranges from long waves (red) to short waves (violet)

Reason warm air rises

-Warm air expands, becomes less dense, and is buoyed upward. -It rises until its density equals that of the surrounding air. -Example: Smoke from a fire rises and blends with the surrounding cool air.

Which melts faster in sunshine—dirty snow or clean snow?

A. DIRTY SNOW B/C absorbs more sunlight, whereas clean snow reflects more.

If a good absorber of radiant energy were a poor emitter, its temperature compared with its surroundings would be

HIGHER. 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 would remain higher than the temperature of the surroundings. Nature is not so!