Conservation of Linear Momentum and Newton's Third Law
If space is a vacuum—that is, if it contains absolutely nothing—then how does a rocket move? Doesn’t it need something to push against?
Rockets can propel themselves through the nothingness of space because of two fundamental laws of physics: Newton’s Third Law and the Conservation of Linear Momentum. Both ideas are essential to understanding how nearly everything in the universe moves. When an ice skater takes off from a dead stop, she digs her blade into the ice and the ice pushes back with an equal and opposite force, sending her gliding across the rink. When a cannon is fired, the cannonball goes hurtling through the air while the cannon recoils backward in response. Both of these principles stem from the same general idea: that the universe likes to keep everything in balance.
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