Forces

There are three main forces acting on the rocket that we shall look at. They are: Gravity, Thrust, and Air Resistance.

THRUST

The thrust of the rocket is the force that propells the rocket. It is created by burning a fuel, which creates a gas, which gets expelled out the back of the engine. Mathematically it is represented by F=Ru where R is the rate of fuel consumption and u is the speed of the gas with respect to the rocket. When doing the math remember that u will always be negative. If you look at a graph of thrust vs. time you will see a large spike at the beginning and then the curve levels off. After about 2 seconds the thrust is 0. This large spike is needed for two reasons. At the beginning it is needed to break the pull of Earth's gravity. As well, the rocket needs to be going quite fast in order to maintain stability. It is the force of the air resistance on the fins that keep the rocket going straight. If the rocket is not going fast enough then the rocket's flight will not be stable as the fins will not experience the forces exerted on them by the wind.

GRAVITY

Gravity is a force that we all experience every day. It is the force that attracts massive objects. The force of gravity on the rocket is written as F=mg where g=9.8m/s2.

AIR RESISTANCE

Air resistance is felt by the rocket, but it is fairly hard to measure and model, so we'll ignore its effects for this demonstration.