The first point to realise is that it was Newton who laid down the foundations for the science of rocketry. A rocket conforms to Newton's 3 Laws of Motion and here we shall look at each law in turn.
- Newton's First Law
- Newton's First Law states that all objects at rest will
remain so unless acted on by an unbalanced force. Thus it is
necessary for an unbalanced force be exerted in order for the
rocket to lift off the launch pad. This force is provided by
igniting the engines and the resulting production of thrust.
- Newton's Second Law
- Newton's Second Law determines the amount of thrust the
rockets will produce. This law is often written as F = ma, but
for clarity here it is possible to restate Newton's Second Law to
read:
Thrust = amount of reaction mass x exhaust velocity
Thus the more fuel that is burnt and the faster the produced gas escapes the rocket, the greater the thrust of the rocket.
- Newton's Third Law
- Newton's Third Law states to every action there is an equal and opposite reaction, this is crucial, the reaction principle is the basis of how a rocket works. All a rocket basically does is expel gas particles at high speed and this may therefore be termed the action. The equal and opposite reaction can be seen as the forward movement of the rocket.
It is also worth mentioning that rockets differ from all other
engines as they carry everything they need onboard. For example
if you compare a rocket engine and a jet engine the main
difference between them is the jet is using oxygen from the air
to enable it to burn its fuel whereas the rocket is carrying its
own oxidiser, this gives it the advantage of being able to fly
where there is no oxygen to use, e.g. space!
It also means that the rockets can achieve a better burn as they
are using pure oxygen and this means they are able to produce
more thrust.