# Moving Energy

Once the energy from the Sun gets to Earth it begins to circulate through different ecological systems. The energy slowly spreads out across the planet. It moves with the water. It moves with the wind. It even moves because the Earth rotates. A good example of large amounts of energy moving is the rising of heated air masses.

# Conduction

Conduction happens when energy is transferred from one molecule to another. You know that if you put cold things next to warm things, the heat moves from the hot area to the cold area. Get some hot sand. Put the sand in a plastic bucket. Do you notice how the bucket warms up? If you put coffee in a mug you'll see that the cold mug heats up right away. The heat conducted from the sand to the plastic. The heat conducted from the coffee to the mug.

Time to go to the beach! The surface of the sand is really hot at the beach. Just a few inches down the sand is really cold. Objects transfer heat at different rates. Scientists call that ability thermal conductivity. Sand has a very low conductivity. At the beach, the sand acts like a big insulator. The sand on the top gets very hot, but conducts very little heat to the ground below.

# Convection

Convection is like the stirring inside of the oceans or on a hot day when you feel wind. Convection happens when molecules move to a new location because they are hot. When you heat matter up it usually expands. When something expands, scientists say it is less dense. Less dense materials rise and move to areas of low density.

Now in English. You have the ocean. It is warmer at the surface than at the bottom. What happens if there is a volcano at the bottom of the ocean? Volcanoes are really hot and it would heat up the water around it. That hot water would rise to the surface of the ocean and colder water would take its place. There would be a movement of large amounts of water.

We're going to the beach one last time. The air over the water is cooler than the air over the land. When air moves onto the shore it heats up and rises. Up goes the air and the cold air moves in to take its place. As the air moves higher, it begins to cool. When it gets cold over the ocean, it sinks down. We've just described something called a convection cell.

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Cosmos4Kids: The Sun
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