The Sun Powers the Water Cycle

0:00Water is always moving around our planet, in a loop called the water cycle. What powers it?

0:07The energy comes from the Sun. Sunlight is absorbed by the ocean and warms the water near its surface.

0:15Some of the warm water evaporates: it changes from a liquid into an invisible gas called water vapour.

0:23Evaporation takes in a lot of energy. The vapour carries this energy as stored heat, called latent heat.

0:32Plants add vapour too, releasing it through tiny pores in their leaves. This is called transpiration, and sunlight drives it as well.

0:41Warm, moist air rises. As it rises, it expands and cools.

0:49When the vapour cools enough, it condenses. It turns back into tiny liquid droplets that form clouds.

0:56So a cloud is not water vapour, which is invisible. A cloud is made of tiny droplets of liquid water or tiny crystals of ice.

1:07When vapour condenses, it releases its stored heat into the air. This heat warms the air and can power big storms.

1:17In the cloud, droplets join into bigger drops. When they are heavy enough, gravity pulls them down as precipitation, such as rain.

1:27On land, gravity keeps pulling the water downhill, and rivers carry much of it back to the sea.

1:35So sunlight powers the water cycle by lifting water into the air, and gravity brings it back down.