We have learned that light energy moves - its waves travel and can be reflected and bounce off of objects. Heat energy moves as well, and it moves in three different ways. Conduction is when heat is transferred from an area of high temperature to an area of cooler temperature by the movement of energy between the particles that make up those materials. When you put your hand against a cold window on a winter's day, the window sucks the heat from your hand by conduction. Another example is when a metal pot is on a hot stovetop. At first, only the bottom of the pot directly touching the stovetop is very hot. Then, the heat energy moves through the metal particles that make up the pot. Eventually the entire pot, and sometimes even the handle, becomes hot. This is conduction of heat through a material.

Convection occurs when a fluid, such as air or water, comes in contact with an object that is at a higher temperature. Have you ever looked at a hot cup of cocoa where the liquid meets the air? You begin to see circulation or swirled patterns appear. This circular pattern happens when the air near the surface of the cocoa gets warmed by the coffee and it rises. The surrounding cooler air falls to take its place and begins a circular motion. This convection pattern will continue until the two substances reach the same temperature.

Many weather patterns occur because of convection. Sea breezes are a good example. During the day, the land warms up faster than the sea. The air above the ground is hot, the air above the water is cold. The hot air above the land rises, and the cold air above the sea swoops in to take its place. This causes a wind to blow from the ocean toward the land, a sea breeze. At night, the situation reverses. The land cools down faster than the sea, so the air above the ground is colder than the air above the water. The hot air above the water rises, the cold air from the land rushes in, and you have a land breeze.

Entry 22: From what you have learned about the Moon, would convection occur on the surface of the Moon like it does on Earth? Why or why not?

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