notes
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 :

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"`