Lesson 33: Air Pressure
Air pressure results from moving gas particles striking surfaces. The lesson connects pressure with gas volume, temperature, and amount, using compression and airflow as examples.
Key Ideas
- Air is made of tiny moving particles. They spread out with spaces between them.
- Air particles bump into surfaces and push on them. This creates air pressure.
- Squeezing the same amount of air into a smaller space raises its pressure, if its temperature stays the same.
- Gases are much easier to squeeze into a smaller space than liquids or solids.
- Air can move from a place with higher pressure toward a place with lower pressure, as when air escapes from a balloon.
Vocabulary
- Gas Particles: The tiny moving atoms and molecules that make up a gas.
- Pressure: How much push acts on each part of a surface.
- Compression: Squeezing material into a smaller space.
- Compressed Air: Air kept at a higher pressure than the air around it.
- Decompression: A drop in pressure, such as when compressed air is released.
Discussion Questions
- Air pushes on your body with about 14.7 pounds per square inch. Why do you never feel that enormous force?
- What does higher pressure inside a bicycle tire mean in terms of particle impacts on its surfaces? Why would you need to know whether a reading is gauge or absolute pressure before comparing it with atmospheric pressure?
- Why is air in a bicycle pump much easier to compress than water? How do particle spacing and interactions help explain the difference?
Hands-On Activity: The Balloon Pressure Test
Students inflate a balloon in stages and record changes in size and resistance. The balloon changes volume and its rubber stretches, so this is not a controlled test of gas pressure alone.
Supply List
- One balloon
- A ruler or tape measure
- A notebook and pencil
Instructions
- Hold the uninflated balloon. Squeeze it. Notice how limp and easy it is to deform. What is inside right now?
- Blow one breath into the balloon and pinch it closed. Squeeze it gently. What is different from step 1?
- Blow two more breaths in. Squeeze again. How has the resistance changed?
- Inflate the balloon fully. Try to squeeze it flat. What is preventing it?
- Measure the circumference of the fully inflated balloon and record it.
- Release the balloon without tying it. Describe where it goes and why. Which direction is air flowing, and what does that tell you about inside vs. outside pressure?
- In your notebook, sketch equal-volume containers of gas at the same temperature, one with fewer particles and one with more. Explain how the more crowded sample can produce more particle impacts and greater pressure. Keep the comparison conditions explicit.