ELI5: How do rockets work in space without air to push against?

Rockets move in space not by pushing against the air, but by throwing heavy stuff out of their backs to push themselves forward.

Imagine you are standing on a skateboard on a flat driveway, holding a heavy bowling ball.

• If you throw that bowling ball forward as hard as you can, the ball flies one way, and your skateboard rolls backward in the opposite direction.
• You did not push against the air to move; you pushed against the heavy ball.

Here are two more everyday ways to picture this:

• The Squirting Garden Hose: If you turn on a garden hose with high water pressure, you feel the nozzle push back hard against your hand. The hose is not pushing against the air; the water shooting out the front pushes the hose backward.
• The Released Balloon: If you blow up a party balloon and let it go without tying it, the balloon zips crazily around the room. The trapped air rushes out of the hole, and that escaping air pushes the rubber balloon forward.

Just like throwing the bowling ball, shooting that gas out of the back pushes the rocket forward. Because the rocket carries its own gas to throw, it does not need any air around it at all. It can fly through the empty, silent void of deep space simply by throwing its own exhaust backward.