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The Gravitational Constant

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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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