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Wind and water

Energy and power · level 1, lesson 5 of 6

A question to start

On a windy day, a kite pulls hard on its string, and washing flaps on the line. A river carries leaves and sticks along. Where do the wind and the river get the energy to push things?

The idea

Anything that moves has energy. Moving air, the wind, has energy. So does moving water in a river or a wave. That is why wind can push a sailing boat across the sea, spin a windmill, or blow your hat off.

People have used this for thousands of years:

  • Sails catch the wind and push boats along.
  • Windmills turn in the wind to grind grain or pump water. Today, wind turbines make electricity.
  • Water wheels turn in rivers; today dams use falling water to make electricity.
windturbine

Where does the wind's energy come from? The Sun warms some places more than others. Warm air rises, cool air moves in to take its place, and that moving air is wind.

On Mars, there is wind, and it can whip up huge dust storms. But the air is so thin that even a fast wind pushes only very gently, about as hard as a light breeze on Earth. A wind turbine on Mars would make only a little electricity. And there are no rivers on Mars today, so no water power either.

Worked examples

1. A pinwheel. Blow on it, or hold it in the wind, and it spins. The moving air gives it energy.

2. A sailing boat. The wind pushes on the sail, and the boat moves across the water.

Try it

  1. Why does wind have energy?
  2. Name two ways people use the energy of the wind.
  3. What makes the wind blow in the first place?
  4. Why would a wind turbine on Mars make only a little electricity?
Answers
  1. It is moving air, and anything moving has energy.
  2. For example: sailing boats, windmills, wind turbines.
  3. The Sun warming some places more than others.
  4. The air there is very thin, so even fast wind pushes gently.

Common mistake

"Strong dust storms on Mars mean very strong winds." The winds can be fast, but in such thin air they push weakly. They are strong enough to lift fine dust, but not to knock over a rover.

Where it leads