Interactive Rocketry Tutorial

THE EFFECTS OF GRAVITY.

All rockets have to work against gravity. Gravity is one of 4 fundamental forces, and is the force from which Black Holes gain their notorious publicity. The larger, or more massive a body, the greater the gravitational attraction it has. So the gravitational attraction of Jupiter (the largest planet in our solar system), is greater than that of the Earth, and the gravitational attraction of the Sun is many times larger than this again.

Back on Earth, the gravity is not anywhere near as strong as that of a Black Hole of course, but it still pulls objects down towards the Earth. Hence the fact that apples fall off trees, and balls thrown into the air fall back down. This is Newton’s 2nd Law at work, where:

(Force = mass x acceleration)

This makes it harder for a rocket to fly into space, because the rocket has to work against gravity. Once in space, the gravity of planets can be used to give a spacecraft a push - this is how the Galileo spacecraft got to the planet Jupiter.

In the case of an apple which falls off a tree, the force equals the mass of the apple multiplied by the acceleration due to gravity. This acceleration due to gravity is 10 metres per second squared on the Earth’s surface. On Mars, it is about 3 metres per second squared.

Question.

So if a rocket has a mass of 1000 kg, and the acceleration due to gravity is 10 m / s -2 , what is the force which the rocket needs to overcome to launch ?

Answer.

Force = mass x acceleration

Force = 1000 kilograms x 10 metres per second squared

Force = 10,000 Newtons.

Questions.

1. What happens if we now move the rocket to Mars ? It still has a mass of 1000 kg but the acceleration due to gravity is now 3 m / s -2 , so what is the new force it must overcome to take off ?

2. The rocket now tries to take off from an asteroid with an acceleration due to gravity of 0.5 m / s -2 , what force must it overcome this time ? (mass = 1000 kg)

This page is maintained by Richard Osborne