This is Newton's Third Law of Motion. Rocket power Rockets can move through space, where there is no air to push against, because of the action and reaction between the burning rocket fuel and the rocket's body. As the rocket fuel burns, it expands, pushing on the rocket nozzle, so the rocket is pushed one way and the burning fuel equally the other. There are many different kinds of force. Some are contact forces - forces which directly push or pull an object, like someone hitting a ball.
Some forces act at a distance.
Gravity, electro-magnetism and the nuclear forces all act at a distance. Forces like these depend inversely on the distance between the two affected objects - that is, they get weaker the further apart they are. You could work out the force used to hit a tennis ball, for instance, by multiplying how fast it accelerates by its mass, or how fast a car can accelerate by dividing the force generated by the engine by the car's mass. If you know the size and direction of all the forces acting on an object, you can also work out in exactly which direction it will move. The mass of water in a big wave is so huge that it has enormous momentum and takes a great deal of stopping.