Gases! They're one of the states of matter, and one of the hardest to get to grips with. A lot of them are invisible and what makes a gas a gas it a bit harder to figure out than what makes a liquid a liquid, or why solids are a solid. After all, you can see and touch (most) liquids and solids.
How were gases discovered in the first place? We have a scientist called Joseph Priestley to thank for much of the discovery. Have a view of this clip to find out how he discovered the gases carbon dioxide (which he called 'heavy air') and oxygen (one you've probably heard of!):
Here's the question I want you to investigate - are all gases the same? What can we use different gases for? We've already looked at 2 - carbon dioxide (which you'll notice has an important use, if you watched the clip!) and oxygen.
You might also want to look up helium, hydrogen, neon, nitrogen and argon. You can set out your work as a poster and include pictures of what each gas is used for!