system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How can we turn swivel chairs without touching the ground, just by jerking our body to one side? Where does the force come from?

Are we pushing air like we push water when swimming?
gpt
Every action has an equal and opposite reaction.

This means that when you move your legs to one side, it pushes the chair to the other side.

But how come you can do it multiple times? 

The answer has to do with friction. Friction steals a bit of the energy from your motion, but it can only take so much (momentum) per unit of time. So if you move slower, more (momentum) will be lost to friction rather than turning the chair. 

That way, you can turn quickly to one side, and then turn slowly back, and you'll end up in a different position than you started.

Edit: (for clarity)