Science
What is Gas?
A gas is a state of matter with no fixed shape or volume — it spreads out to fill whatever container it's in. Its particles are far apart and move quickly in all directions, so a gas can be compressed or expanded far more than a solid or liquid.
See it, don’t just read it.
Watch a 2-minute lesson with voice + animation that explains gas.
Key things to understand
- 1A gas has neither a fixed shape nor a fixed volume — it expands to fill any space available.
- 2Its particles are far apart and zoom around freely, colliding with each other and the container walls.
- 3Those collisions with the walls are what we feel as gas pressure.
- 4Because there's so much empty space between particles, gases are easily compressed.
- 5Cooling a gas enough condenses it into a liquid; the air around us is a mix of gases.
Frequently asked questions
- Why does a gas fill its container?
- Its particles have lots of energy and are barely held together, so they fly apart in all directions until they spread evenly through whatever space they're in.
- What is gas pressure?
- It's the force from gas particles constantly colliding with the walls of their container. More particles or more heat means more collisions — and higher pressure.
- Why can gases be compressed but liquids can't?
- A gas is mostly empty space between far-apart particles, so squeezing pushes them closer. A liquid's particles are already close together, leaving little room to compress.