Gravitation: Overview, Questions, Preparation

We, humans, observe that an object dropped from a height falls towards the earth. We know that all the planets revolve around the sun. The moon revolves around the planets. There must be some force acting on the objects in all these cases—the force of gravity. When the apple hit Sir Issac Newton on the head, he concluded that the same force handles all these things. This force of attraction between the objects known as the gravitational force.

Every object with a certain mass attracts other objects with a gravitational force, which is directly proportional to their masses’ product and inversely proportional to the square of the distance between them. The force is along the line joining the centres of two objects.

Let’s look at the formula:

F = Gravitational Force between two objects;

G= Constant of proportionality also called Universal Gravitation Constant, which is equal to 6.673 × 10^–11 N m^2 kg^–2;

M and m are the two masses lying at a distance d.

If there is no Earth or no other planets, the moon will continue going in a straight line. The gravitational pull of Earth draws the moon closer to it. The moon’s gravitational force is vital to earth as it keeps Earth from rotating faster or changing its rotational angle. The moon’s gravitational pull of Earth accounts for the rise and fall of ocean tides. A high tide creates where the moon’s gravitational pull is strongest. 

Gravitational Force of the Moon in Class 11

This chapter’s questions are based on the ‘Universal Law of Gravitation,’ ‘Acceleration Due to Gravity,’ and Kepler’s Law. The topic ‘Gravitational Force of the Moon’ has less weightage, compared to others.

Example 1: How to calculate the gravitational force of the moon?

Solution:

Formula  g= GM/r^2

Mass of moon(M) =7.36* 10^22

Radius of the moon(r) = 1.74* 10^6 

G = 6.673 × 10^–11

So, g= 6.673 × 10^–11(7.36* 10^22)/1.74* 10^6  = 1.625 m/s^2.

Example 2: How to calculate the weight of the object on the moon?

Solution: The weight of the object on the moon is the force with which the moon attracts that object.  

• Mass of an object =m
• Weight on the moon =Wm
• Mass of the moon =Mm
• Radius = Rm

Images courtesy: NCERT

Q: What is the importance of gravitational force?

Q: Why is moon’s gravitational force less than that of the earth?

Q: What is the acceleration due to gravity?

Q: Why does moon’s gravity cause tides on earth but not the sun’s tides?

Q: Does the moon affect humans?