The gravitational constant (G) is a proportionality constant that appears in the equation for Newton's law of gravitation. The value of G is approximately equal to $6.67×10_{−11}Nm_{2}kg_{−2}$.

definition

Experimental method to determine the value of gravitational constant

The experimental setup performed by Cavendish is shown in the attached figure. Two masses are attached to the end of a horizontal suspended bar. Then, two large lead spheres are brought close to the small ones but on opposite sides. There is no net force on the bar but a non-zero torque acts on it caused due to gravitational force of attraction. This cause twisting of the suspended wire until a maximum angular displacement. At the point of maximum angular displacement, restoring torque is equal and opposite to the gravitational torque. $d_{2}GMm L=τθ$ where $τ$ is the restoring couple per angle of twist and is constant for a given material.