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Wind pushes

Air and fluids · level 1, lesson 4 of 6

A question to start

A kite has no engine, and a sailing boat has no motor. What makes them move?

The idea

Moving air pushes on whatever is in its way. People have used that push for thousands of years.

  • A kite catches the wind and is pushed up into the sky.
  • A sail catches the wind and pushes a boat across the water.
  • A windmill has big blades. The wind pushes them round, and they turn a machine.

Two things make the push bigger:

  • a faster wind, and
  • a bigger thing to catch it: a bigger sail, kite or blade.
windkite
A wind that pushes Mars Earth
How much air there is very little: Mars's air is thin plenty
What it takes to fly a kite a much faster wind a breezy day

On Mars, the air is so thin that NASA says a kite would need a much faster wind to fly than on Earth.

Worked examples

1. A big sail and a small sail in the same wind: the big sail catches more wind and gets the bigger push.

2. A pinwheel. Blow on it gently and it turns slowly. Blow hard and it spins fast.

3. No wind. On a still day, a kite will not go up unless you run with it. Running makes the air rush past it.

Try it

  1. What pushes a sailing boat along?
  2. Give two things that make the wind's push bigger.
  3. Why does running help a kite go up on a still day?
  4. Would it be easier or harder to fly a kite on Mars?
Answers
  1. The wind pushing on its sail.
  2. A faster wind, and a bigger sail or kite to catch it.
  3. Running makes the air rush past the kite, just like wind.
  4. Harder. The air is so thin that the wind has to blow much faster.

Common mistake

"Wind only pushes light things." Wind pushes everything in its way. Light things move more, but strong winds can push over trees and even move big ships.

Where it leads