Introduction
This is a force with which the earth attracts objects towards its centre. If you throw a coin up, what do you expect? You will notice that the coin will go up and at a certain point stop before beginning to come down. Is there anything pulling the coin down? Yes, although you may not see anything pulling it. The force due to gravity, is pulling the coin to the centre of the earth.
Assuming you are holding a mass of 20g in your hand. Climb a tree or a high object. Release the mass, what do you notice? You will notice that the weight did not go horizontally but vertically.
There is a force acting on that mass downwards. That is to say there is a force attracting the mass to the centre of the earth. If two objects of the same density are released from a height at the same time, do you think they will fall at the same time? What happens if they have different densities like a coin and a feather? Two objects of the same density will fall at the same time while two objects of varying densities like a coin and a feather will not fall at the same time. The coin will fall faster than the feather. This is so because of air resistance on the feather. If air is removed and we now have a vacuum, the two objects of varying densities will fall at the same time.
Calculation of Gravitational Force
Imagine an object of mass M kilogrammes raised from the ground level to a height h metres above the ground
The force of gravity on the mass = mg
Where g is the acceleration due to gravity in metres per second squared (ms-2)
The workdone against gravity in raising the mass is
= Force x distance moved
= mg x h
= mgh
If M is in kilogrammes, g in ms-2 and h in metres
Then force = mg in Newtons
Workdone = mgh in joules
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