"How Heavy am I in Space?" Return to list of pracs

Aim: This activity is used to illustrate how heavy we are on other planets in our Solar System.

Method: Look carefully at the table below on the worksheet and consider a typical 90kg astronaut. What is the astronaut's mass on Neptune? Work out the weight of the astronaut on each planet. Where is the astronaut's weight the greatest? Where is it the least? What happens to the astronaut in outer space? What problem does this cause, and how are they solved in space travel?

Place	Gravity compare to Earth (N/Kg)	Mass (kg)	Weight x force (N) (mass x gravity)
Mercury	4	90	360
Venus	9	.	.
Earth	9.8	90	.
Outer Space	0	.	.
Moon	1.7	.	.
Mars	4	.	.
Jupiter	26	.	.
Saturn	11	.	.
Uranus	10	.	.
Neptune	15	.	.

Background knowledge: Gravity is the amount of force that a massive object (like stars and planets) have on objects. The larger the masses of the two objects, the greater the force of gravity. Even on the small scale objects exert forces of gravity on each other. When you are in your classroom, any one student exerts a gravitational force of attraction with any other student in the room. Therefore, you are attracted to your desk ... the desk is attracted to the student in the front row ... the student in the front row is attracted to the door etc. Only because they are on such a small scale (compared with planets) do you not notice it.

Why it happens? People are still trying to find out that question. They have found small sub atomic particles called gluons which do the "attracting". Isaac Newton first discovered the nature of gravity back in the 19th century (the good old apple falling on his head story). Previous to this, scientists thought that matter existed according to the laws of Aristotle. They thought that all matter was made up of earth, air, fire or water and depending upon what propertied they have will dictate what proportions of each material exist within them. Therefore, a cannon ball is made of earth since if released it moves towards its natural state of matter ... the earth. Kites are made of air or fire since when you release them they fly up into the sky. Roads on hot days must be mainly made of earth but carry some fire in them since they can get hot like fire.

The most interesting thing is if you were on Earth the rate of gravity is 9.8 metres per second squared. This means that any object will speed up at a rate of 9.8 metres every second (35km/h) every second. This means an object, starting from stationary, will get to a speed of 35km/h after 1 second ... then 2 x 35km/h = 70km/h after 2 seconds ... then 3 x 35km/h = 105km/h after 3 seconds etc. Kicking a football or jumping in the air will be relative to this gravity value. If the record for a high jump is 1.5 metres then on Mercury you will be able to jump (9.8/4) x 1.5 = 3.7 metres in the air ... on the Moon you will be able to jump (9.8/1.7) x 1.5 = 8.6 metres in the air ... on Jupiter you will only be able to jump (9.8/26) x 1.5 = 0.6 metres in the air!