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# The Gravitational Constant

#### Gravitational Constant

Newton’s view of Gravitation

• Newton was the first scientist who studied the force of gravitation.

• According to him there is a force which is exerted by the surface of the earth because of which all the objects are attracted towards the surface of the earth.

• He also concluded that all objects in this universe attract each other with a force. This force is Gravitation force.

#### Gravitational Constant: Cavendish experiment

• Cavendish performed an experiment to calculate the value of G.

• To calculate the value of G he took a wooden plank and attached two 2 balls on either side of the plank and hung this with a thin thread from the top.

• He introduced 2 very big balls and those balls are near the smaller balls.

• He observed that the small balls got attracted to big balls and wooden plank started rotating and as a result the thin thread started twisting.

• This happened because of force of attraction between the small balls and bigger balls.

• He observed that :-

1. Plank rotates till twisting force becomes equal to the gravitational force between the balls.

tau = ("G" m_1m_2)/r^2

Ltheta=("G"m_1m_2)/r^2

• By using the above equation he calculated the value of G,

• "G" = 6.67xx10^-11"Nm"^2//"kg"^2

• Units of G: Nm2/kg2

Problem:- Calculate the gravitational force of attraction between 2 lead balls of mass 20kg and 10kg separated by a distance of 10cm?

Answer: m1= 20kg, m2=10kg, r=10cm = 10/100 = 0.1m

"G"=6.67xx10^-11"Nm"^2//"kg"^2

"F"("G"m"1m2)/r^2

"F"=1.3xx10^-6"N"

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