AP Board Class 9 Physical Science Chapter 7 Gravitation

Students have learnt about uniform accelerated motion and laws of motion in the earlier chapter called ‘motion’. However, in Chapter 7 of Andhra board Physical Science textbook, students will study about gravitation and uniform circular motion which is an example of non-uniform accelerated motion. Some of the important topics covered in this unit are;

• Centripetal Acceleration And Centripetal Force
• Centre Of Gravity
• Law Of Gravitation
• Weight
• Weightlessness
• Free Fall

Uniform Circular Motion

Uniform circular motion is described as the motion of a body with constant speed in a circular path.

Law Of Gravitation

According to the law of gravitation, a body having a certain mass will experience an attractive force that is directly proportional to the product of their masses. However, the force is inversely proportional to the square of the distance between the two objects.

Centripetal Acceleration

The acceleration, which is always directed towards the centre of the circle or a force that makes a body follow a curved path is known as centripetal acceleration.

Centripetal Force

The net force required to keep a body in uniform circular motion is called “Centripetal force”. It is mostly directed towards the centre around which the body is moving.

Free Fall

A free fall is a motion of a body when the force of gravity acts on it. During free fall condition, a body experiences a state of ‘weightlessness’.

Centre Of Gravity

The point, where the total weight of the body acts is known as the centre of gravity. It is the point, at which the weight of a body is evenly dispersed and all sides are in balance.

Students can take a closer look at some of the important chapter questions that are given below.

Question 1: Define the weight of an object.

Answer: The weight of an object is the force of gravity acting on it. W = mg

Question 2: What would happen to your weight if the mass of the Earth was increased by 15%?

Answer: Generally, if we change the mass of a body, there will be a change in the force of gravity. Suppose, the mass of the earth goes up by 15 percent, then the force of gravity that you will experience or your weight will also increase by15 percent.

Question 3: What was the inspiration for the Law of Gravitation?

Answer: The idea or the law of Universal Gravitation was inspired by the incident where an apple fell from a tree and Sir Issac Newton was there to observe this phenomenon.

Question 4: Define Uniform Circular Motion.

Answer: “Uniform circular motion is a motion of the body with a constant speed in circular path.”

Question 5: What is Centripetal Force?

Answer: The net force required to keep a body in uniform circular motion is called “Centripetal
force”. F_C = Mv² / R.

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