Blowing on Paper
Hold a piece of paper at the two corners at the ends of its longest side. What happens when you blow across the paper?
|Thinking about Lift
Blowing across the top side of the paper makes the paper go upwards, while blowing across the underside has little effect.
When you blow across the top of the paper, you are speeding up the air which is pressing down on the paper and it cannot press down so much. The paper now gets pushed up by the air underneath. The force of the air pushing the paper upwards is the force called LIFT.
Here's another way to think of it: When air is moving fast past the paper, its pressure is lowered. The air pressure under the paper is now greater than the air pressure on top of the paper and the paper is moved upwards.
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