**1** **State the universal law of gravitation**

The universal law of gravitation states that every object in the universe attracts every other object with a force called the gravitational force. The force acting between two objects is directly proportional to the product of their masses and inversely proportional to the square of the distance between their centers. For two objects of masses m 1 and m 2 and the distance between them r, the force (F) of attraction acting between them is given by the universal law of gravitation as:$\\$ $F=\dfrac{\text{G$m_1m_2$}}{r^2}$$\\$ Where, $G$ is the universal gravitation constant given by:$\\$ $G=6.67*10^{11}Nm^2 kg^{-2}$

**2** **Write the formula to find the magnitude of the gravitational force between the earth and an object on the surface of the earth.**

Let $M_E$ be the mass of the Earth and m be the mass of an object on its surface. If R is the radius of the Earth, then according to the universal law of gravitation, the gravitational force (F) acting between the Earth and the object is given by the relation:$\\$ $F=\dfrac{Gm_1m_2}{r^2}$

**3** **What do you mean by free fall?**

Gravity of the Earth attracts every object towards its centre. When an object is released from a height, it falls towards the surface of the Earth under the influence of gravitational force. The motion of the object is said to be free fall.

**4** **What do you mean by acceleration due to gravity?**

When an object falls freely towards the surface of earth from a certain height, then its velocity changes. This change in velocity produces acceleration. This acceleration is known as acceleration due to gravity (g). The value of acceleration due to gravity is $9.8 m/s^2 .$

**5** **What are the differences between the mass of an object and its weight?**

$\textbf{Mass}$$\\$ $\to$ Mass is the quantity of matter contained in the body$\\$ $\to$ It is the measure of inertia of the body.$\\$ $\to $ Mass is a constant quantity.$\\$ $\to $ It only has magnitude.$\\$ $\to $ Its SI unit is kilogram (kg).$\\$ $\textbf{Weight}$$\\$ $\to $ Weight is the force of gravity acting on the body.$\\$ $\to$ It is the measure of gravity.$\\$ $\to$ Weight is not a constant quantity. It is value is different at different places.$\\$ $\to$ It has magnitude as well as direction.$\\$ $\to$ Its SI unit is the same as the SI unit of force, i.e., Newton (N).