For every action, there is an equal and opposite reaction

Like most engines, rockets burn fuel. Every action has an equal and opposite reaction. So the third law basically says that if you shoot out an object in one direction you will move in the other direction. This is how rockets work in a vacuum. They have a source of fuel which is heated up so that it expands and is pushed out of the rocket.

Liquid-fuel engines pump liquid hydrogen (the fuel) and liquid oxygen (the oxidizer) into a combustion chamber at the bottom of the rocket, burn the mixture (which is called the propellant, because it propels the rocket), and allow the hot exhaust to escape through a jet nozzle to produce thrust.

How does a rocket engine work?

When a rocket shoots fuel out one end, this propels the rocket forward — no air is required.

NASA says this principle is easy to observe on Earth. If you stand on a skateboard and throw a bowling ball forward, that force will push you and the skateboard back. However, because your weight on the skateboard is heavier than that of the bowling ball, you won't move as far.

That's the challenge engineers face when designing space engines.  A small amount of thrust does push the spacecraft forward, but it often takes a great deal of fuel to get going anywhere quickly. More fuel means more weight, which adds to the cost of a mission. 

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Nose cone and rocket diameter affect drag. The amount of air resistance that opposes a rocket's motion depends mainly on the shape of the nose cone, the diameter of the rocket and the speed of the rocket. The first point that meets the air is the nose cone at the front end of the rocket.

What is the purpose of a nose cone?