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Squash a gas with a piston, or heat it: how does its volume change?
Gas Laws lab · Last updated: 16 October 2026
You squash a gas with a piston, then heat it, and watch how its volume changes. Behind the scenes, tiny particles are crashing into the walls. They find out why a bicycle pump gets harder to push, why balloons shrink in the cold and why aerosol cans warn you to keep them away from heat.
What you'll discover
- Gas pressure comes from countless particles hitting the walls of their container.
- Squeezing a gas into half the space, at the same temperature, doubles its pressure.
- Heating a gas makes its particles move faster, so at the same pressure it expands.
The science in plain words
A gas is made of particles moving fast in all directions, with lots of empty space between them. Every time they hit the walls of their container, they push on them. Billions of these tiny pushes add up to the gas's pressure. Because there is so much space between particles, gases are easy to squash, unlike solids and liquids.
If you push a piston in and halve the volume while keeping the temperature the same, the same particles are crowded into half the space. They hit the walls twice as often, so the pressure doubles. This is Boyle's law: at a fixed temperature, pressure times volume stays the same. You feel it when a bicycle pump gets harder to push as the air inside is squeezed.
Heating a gas makes its particles move faster, so they hit the walls harder and more often. If the gas can expand, as in a balloon or a cylinder with a loose piston, it grows until the pressure balances again. This is Charles's law: at fixed pressure, the volume is proportional to the absolute temperature, measured from absolute zero, minus 273.15 °C. A balloon shrinks in the cold and swells again in the warm. If the gas cannot expand, its pressure rises instead, which is why aerosol cans must be kept away from heat.
Where it fits
- India, NCERT: Class 9 science, Chapter 1: Matter in Our Surroundings
- India, NCERT: Boyle's and Charles's laws go beyond the NCERT syllabus for classes 6 to 10; the lab builds on Class 9 Matter in Our Surroundings.
- United States: Grades 6 to 12
- Next Generation Science Standards: MS-PS1-4
Common questions
What is Boyle's law in simple words?
Boyle's law says that if you keep a gas at the same temperature, squeezing it into a smaller space raises its pressure in proportion. Halve the volume and the pressure doubles. This happens because the same particles hit the walls more often in a smaller space.
Why does a balloon shrink in the cold?
In the cold, the air particles inside the balloon slow down and hit the rubber less hard and less often. The pressure inside drops, so the stretched rubber squeezes the balloon smaller. When it warms up again, the particles speed up and the balloon swells back.
Why are gases easy to compress?
In a gas the particles are far apart, with mostly empty space between them. Pushing on a gas simply moves the particles closer together. In solids and liquids the particles are already touching, so there is almost no space left to squeeze them into.
Related labs
- States of Matter: Solid, liquid, gas: the same molecules, just jiggling harder.
- Heat Transfer: Bridge hot water and cold with a metal bar. Which metal carries heat best?
- Hydraulics: Push a little piston gently. Can the oil lift a heavy crate?
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Try it yourself
The Gas Laws lab is one of the interactive 3D science labs inside Taz. Change one thing, predict what will happen, then run it and watch. Labs open after you sign in.