The force of gravitation is:

The distance between the centre of the moon and the earth is $D$ and the mass of the earth is $81$ times the mass of the moon. At what distance from the centre of the earth will the net gravitational force on an object be zero?

The tidal waves in the sea are primarily due to

$A$ system consists of three particles each of mass $m_1$ placed at the corners of an equilateral triangle of side $\frac{L}{3}$. $A$ particle of mass $m_2$ is placed at the midpoint of any one side of the triangle. Due to the system of particles,the force acting on $m_2$ is

From a sphere of mass $M$ and radius $R$,a smaller sphere of radius $\frac{R}{2}$ is carved out. For the configuration shown in the figure where the distance between the center of the original sphere and the center of the removed sphere is $3R$,the gravitational force between the two spheres is:

According to Newton's law of gravitation,both the Earth and an apple exert equal forces on each other. Why does the apple fall towards the Earth,but the Earth does not move towards the apple?