The Importance of Gravity

The law of gravity applies to almost everything in the universe. Any two objects pull together like any other two galaxies. In addition, the attractions are small, even zero sometimes, when the distance is large enough.

You can find your value in the way all the stories come together. For example, you may have seen astronauts floating in space. That is because of the lack of gravity in the atmosphere. Therefore, you see that you can walk the earth because of the force of gravity.

Example: An object of mass 40 Kg experiences a force of 200N towards the center of a planet from a distance of 20Km. Find the mass of the planet.

Solution: Let mass of the planet = M, Mass of the object (m) = 40Kg, Distance between both the masses (r) = 20000m, Force due to gravity (F) = 200N.

Therefore,

F=GMmr2�=����2

200=6.673×10−11×M×40(20000)2200=6.673×10−11×�×40(20000)2

M = 2.997 x 10¹⁹ Kg

Mass of the planet is 2.997 x 10¹⁹ Kg

Question: Force between mass of two objects is 40N. If one of their masses is 2 kg and the distance between them is 1m, find the mass of the other object.

Solution:

F=GMmr2�=����2

40=6.673×10−11×M×2140=6.673×10−11×�×21

m = 2.99 x 10¹¹ Kg.

Question: Find the magnitude of the gravitational force between the earth and a 1 kg object on its surface.

Solution: From Newton’s law of gravitation, we know that the force of attraction between the bodies is given by  

F=Gm1m2r2�=��1�2�2

m₁ = 6.4 x 10⁶

m₂ = 1 kg

r = 6.4 x 10⁶

From  the above equation,

F=6.4×1011(6.4×1024)×1(6.4×106)2=9.8N�=6.4×1011(6.4×1024)×1(6.4×106)2=9.8�

Hence, earth exerts force 9.8 N on a body of mass of 1 Kg.