Can you think of two particles which do not exert gravitational force on each other?

Which of the following pairs particles cannot exert nuclear force on each other ?

What do you know about the gravitational force?

If the separation between two particles is doubled, the gravitational force between the particles becomes half the initial force.

If the distance between two particles is halved, the gravitional force becomes

If the separation between two particles is halved, the gravitational force between the particles becomes half the initial force. State true or false.

Universal law of gravitation states that every object exerts a gravitational force of attraction on every other object. If this is true, why don't we notice such forces? Why don't the two objects in a room move towards each other due to this force?

Three identical particles, each of mass m, are located in space at the vertices of an equilateral triangle of side length a. They are revolving in a circular orbital under mutual ravitational attraction. Find the speed of each particle. Find the acceleration of the centre of mass of a system comprising of any two particles. Assume that one of the particles suddenly loses its ability to exert gravitational force. Find the velocity of the centre of mass of the system of other two particles after this.