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Science project idea

Blow over a paper strip and watch it rise: fast air, low pressure

When you blow across the top of a paper strip it lifts instead of staying down. Fast-moving air has lower pressure than still air, so the stronger pressure below pushes the paper up.

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What it shows

When you blow across the top of a paper strip it lifts instead of staying down. Fast-moving air has lower pressure than still air, so the stronger pressure below pushes the paper up.

The science

In moving air, pressure is lower where the air moves faster. This idea is called Bernoulli’s principle. When you blow over the top surface of a paper strip, the air above it moves fast and has lower pressure than the still air below the strip. The higher pressure below pushes the strip up. Aeroplane wings are shaped so the air above moves faster, which gives lift.

Materials

Cost: free. Many items come from home or from waste; spare parts such as LEDs, motors and wire are in the store.

  • A sheet of A4 paper cut into strips of 4 cm by 20 cm
  • Two light paper cups or empty cans
  • A drinking straw
  • Two ping pong balls or light paper balls
  • Tape
  • A ruler
  • A table

Safety

For this project: No special safety. Do not blow too hard or too long so you do not feel dizzy.

Never use mains electricity: power models with cells, batteries or a low-voltage adapter. Sharp and hot tools, flames and lab chemicals need an adult or your teacher beside you. Keep magnets, button cells and small parts away from young children, and wash your hands after making.

All the safety rules

Step by step

8 steps. Do them in order, and test each part before you go on to the next. Write what you notice in a notebook as you go.

  1. Hold one end of a paper strip just under your lower lip so the strip hangs down in a curve.

  2. Blow gently straight forward over the top of the strip and watch it rise and float.

  3. Place two paper cups on their sides, 5 cm apart, and put a ping pong ball between them on the table.

  4. Blow through a straw into the gap between the cups. Notice that the ball does not blow away but stays between them.

  5. Hang two paper strips side by side from a ruler with a gap of 3 cm. Blow down between them and watch them come together.

  6. Draw each experiment and mark where the air is fast and where it is slow.

  7. Make a paper strip wing, folded over a straw, hang it from a thread and blow on it to see it lift.

  8. List three places where this effect is used, such as an aeroplane wing, a spray bottle and a chimney.

What you should see

The paper rises when you blow across it and the two hanging strips move together when you blow between them, showing lower pressure where the air moves faster.

Viva questions

A teacher or a judge will ask how it works. Try to answer each question before you open it, then compare.

1What happens to the pressure of air that moves fast?

It becomes lower.

2Why does the paper strip rise?

The still air below is at higher pressure than the moving air above, so it pushes the paper up.

3Why do the two strips come together?

Fast air between them has lower pressure than the air outside, which pushes them together.

4How does this help an aeroplane fly?

Air moves faster over the curved top of the wing, giving lower pressure above and a lifting force.

Free ebook: Viva Questions for Science Projects

Take it further

Make a paper aeroplane wing with a curved top and measure how far it glides with different curves.

Change one thing, measure what happens, and add a table or chart of your readings: that is what turns a model into your own investigation.

Free ebooks for this project

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