In this activity, students watch the counterintuitive reaction of a candle flame towards fast moving air.

Bernoulli's Principle: As the speed of air increases, the pressure decreases.

When you blow against one side of the flame, you are creating an area of low pressure (the faster the air moves, the lower the pressure).

The relatively high-pressure air on the other side of the candle will rush over to fill the area of low pressure ("winds will blow from high to low"), effectively pushing the flame over so that it bends towards the straw.

### Objectives

• Explain how air pressure works.

• Describe the Bernoulli Effect.

### Materials

• Per Demo:
candle
candle holder
matches
straw

### Key Questions

• Draw a model of the experiment.
• Based on Bernoulli’s principle, where are the high-pressure and low-pressure zones when you blow through the straw?
• Based on your answers, why does the flame bend towards the straw and not away from it?

### What To Do

1. Light the candle.
2. Stand beside the flame, so that the students can see.
3. Ask the students what will happen if you blow hard off to the right or left of the flame?
4. Using the straw, aim to one side of the flame and blow really hard.
5. Move the straw to the other side and repeat the experiment

### Extensions

• Fascinating fact: The shape of the flame is due to the differences in air pressure surrounding the flame.
• In outer space, the flame would be a PERFECT SPHERE.

### Other Resources

Science World | YouTube | The Bernoulli Principle and an Air Cannon!

Science World | YouTube | How to Explore Bernoulli’s Principle with Two Pieces of Toilet Paper

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