# Physics AQA A2 - Gravitational Fields

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• Created by: Ryan
• Created on: 08-01-13 10:56

Gravitational Fields

When you throw an object into the air it comes back down, this is due to the gravitational attraction between the earth and the object. There is a gravitational attraction between any two objects when they are put near each other this this is caused by the gravitational field around the object.

If a small mass is placed near a large mass then the small mass and the large mass will attract each other with equal and opposite forces although this force is not big enough to noticeably move the large mass. The small mass would however move towards the large mass, the path that it would take is called a field line or line of force.

The strength of a gravitational field , g, is the force per unit mass on a small test mass placed in the field.

The test mass must be small enough so that it's field does not move the large mass which would alter it's field. The attractive force that the small mass feels will change depending on where it is in that field, if a small test mass, m, is placed at a certain position in a gravitational field where it is acted on by the gravitational force , F, the gravitational field strength at that position is: g=F / M the unit of this is N.kg^-1.

The weight of an object is equal to mg it is the gravitational force on an object with mass, m, F=mg. If this is the only force acting on the object then it's acceleration is: rearranging F=ma to give F/m=a, as force is equal to mg a=mg/m, the m's will cancel to leave a=g this shows that if a mass is placed in a gravitational field with no other forces acting on it, then it will accelerate with acceleration…