Investigation in to how the force of gravity on a satellite and the radius of the orbit affects the speed necessary to maintain the orbit of the satellite

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Satellite Orbit Investigation

Aim

To investigate how the force of gravity on a satellite and the radius of the orbit affects the speed necessary to maintain the orbit of the satellite.

Prediction

When a satellite orbits round a planet it moves in a circular motion. An example of a satellite is the moon moving round the Earth. A satellites speed stays the same because speed = distance/time and it is always taking the same time to travel a certain distance. However its velocity changes because velocity is speed in a direction. Speed is a size but velocity is a size and a direction. As a satellite orbits a planet it changes direction constantly. If something is moving in a circular motion needs a force to change its direction constantly. This force is called a centripetal force. For a satellite moving round a planet this force is gravity. The direction of this force is towards the centre of the planet.

In our experiment we will be using a rubber bung attached to a piece of string. The bung will represent the satellite and the tension in the string will act as a centripetal force.

When a satellite is orbiting a planet it is accelerating even though its speed is constant. It is accelerating towards the centre of the planet but it doesn't crash because their sideways motion is so fast that the fall matches the curve of the planet. Gravity pulls things to the centre of the Earth; it also determines the motions planets and satellites. The reason it is accelerating even though its speed is constant is because acceleration = change in velocity/time taken. Its velocity is changing due to the change in direction; therefore the satellite must be accelerating - acceleration is a change in velocity per unit of time. Acceleration involves either a change in speed or direction. Things accelerate because the force pushing the forwards is greater than the force pulling them back.

A geostationary orbit is where the satellite is orbiting at exactly the right distance away at the right speed so it appears to stay in exactly the same place over the Earth.

For a satellite to be in orbit it needs to be at a certain speed depending on the force acting on it and how far away it is from the planet. This keeps it in orbit and prevents it from flying off into space. The larger the force acting on it the faster the satellite will travel. We know this because force = mass x acceleration, which means acceleration = force/mass. For example if the mass is 2 and the force is 4 then 4/2 = 2, if we increase the force to 6 then 6/2 = 3 - a larger acceleration. The radius of the orbit also affects the speed of the orbit. If the force is kept constant as it will be in our experiment then the speed of the satellite will increase. However with a satellite orbiting a planet the further away it is from the planet the slower it will travel. This is because as the satellite moves further away from the planet the force of gravity decreases so the speed will also decrease. The size of the bung also affects the speed, the larger the bung the slower it travels.
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In our experiment their will be different weights attached to the string which represents the centripetal force. The length of the string is how far the satellite (the bung) is from the centre (the metal pipe). This means that as we increase the force we expect the speed to be faster and as we increase the radius we expect the speed to be faster also.

We did some preliminary work. We used the same equipment as for this experiment. We swung the bung round 10 times then worked out the speed. These are our results:

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