Review 7th. (for Friday, May 22).

Content:
23-1 How Heat Gets Around. p 420 S165- S167

23-2 Conduction- Heat Transfer Through a Material. p 424

23-3 Convection- Heat Transfer by Currents. p 431.S165-S170

23-4 Radiation- Heat in a Hurry. p 437. S166-S168

Heat always flows from a hotter place to a cooler place.

Conduction occurs when heat flows through a substance or between substances that are in contact with one another Heat transfer by direct contact between heated particles. Radiation occurs when heat travels through empty space or through a transparent material, without heating the space or the material between the heat source and the heated object. Convection: the transfer of heat in a liquid or gas as groups of heated particles move from one region to another. Occurs when heat is transported as a result of the movement of the heated material.

Show how conduction, convection, and radiation can be compared to the way a football is moved around a playing field. (kicking represents radiation, handing the football from player to player represents conduction, and running with the football represents convection). .

Why is it possible to boil the water (on a paper cup) without burning the cup? Heat is conducted through the paper to the water so that both the cup and the water remain at about the same temperature. Water boils at a lower temperature than that at which the cup burns, so the water boils first.

Some materials are better conductors of heat than others. The conduction rate of a material is affected by its composition and size, by the temperature of the heat source, and by the distance of the material from the heat source. Insulator is a material that slows down the flow of heat or carry heat very poorly.

Good conductors of heat include copper, brass, and iron (metals). Poor conductors or insulators are plastic, air, rubber, glass and wood.

Air is a poor conductor of heat. Small air pockets in wool, fur and feathers help to keep heat from passing through these material. As a result, body heat becomes trapped between a person’s body and a garment made from wool, fur, or feather.

Hot or warm air tends to rise, and cold or cool air tends to fall. In a liquid or gas system, convection currents will occur if the temperature is colder at the top of the system than at the bottom of the system. Convection occurs when heat travels as a result of the movement of the material being heated. It is the difference in temperature from one point to another that determines whether convection will occur.

In a sunny day, the air above the land is warmer than the air above the water. The warmer air above the land rises and cooler air from the water moves in, causing the sea breeze. At night the reverse happens. The land becomes cooler than the water. The warmer air above the water rises and the cooler air from the land moves in to take its place. Water can absorb more heat than land and land loses its heat more quickly.

Through what kinds of substances does heat travel by convection? Liquids and gases.

Why doesn’t convection occur in solids? Convection depends on the motion of the material. In a solid the material is not free to move as it is in a gas or liquid.

How is heat transferred from the sun? electromagnetic radiation.

How is the heat from the sun redistributed? By winds and ocean current.

What determines weather and climate? Movement of heat through the oceans, atmosphere and land. Which depends on the angle of the sun’s rays, the density of the atmosphere and the rotation of the Earth.

Greenhouse effect (the trapping of the radiant heat by the Earth’s atmosphere). Infrared waves get trapped by some gases in the atmosphere, such as water vapor, carbon dioxide and methane, causing the Earth to become even warmer.

Two Causes of the increase of carbon dioxide in the atmosphere. Clearing the forest and burning of fossil fuels.

Major contributors to the greenhouse effect: water vapor, carbon dioxide, and methane.

Possible effects of the greenhouse effect: global increase in temperature which could result in a change in the sea level (melting of poles)

Possible solution to the greenhouse effect: Reducing the use of fossil fuels, reducing emission from automobiles and factories. Planting new trees, etc.

Why the earth is not heated evenly? Because of the Earth’s curved shape. Polar regions receive much less solar energy than the regions near the equator.

Convection causes air to move between the Earth’s cold and warm region. Almost all winds are driven by convection patterns that occur because of uneven heating of the Earth’s surface.

What is a convection cell? A complete circle of moving liquid or gas cause by temperature differences. Ex. Cycle of air heating, rising, cooling and returning to the ground.

Role of water in the moderation of the climate. Water is able to store much more heat energy than land. Large bodies of water tend to moderate the climate of nearby areas.

What Hurricanes are? Are giant natural heat engines that feed on the thermal energy contained in tropical seas. These huge storms typically form in the tropics and then veer into the temperate zones, dissipating enormous amounts of tropical heat as they go.

White color reflect most of the radiant energy.

Dark color absorb most the the radiant energy.