CBSE Class 9 Science Chapter 10: Gravitation NCERT Solutions

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NCERT Solutions PDF Class 9 PDF

CBSE Class 9 Science Chapter 10, Gravitation, introduces students to the fundamental principles governing the attraction between objects with mass. This chapter explores Newton's Universal Law of Gravitation, detailing how the force of attraction between any two bodies depends on their masses and the square of the distance separating them. It further explains the concept of free fall, where an object accelerates downwards solely due to Earth's gravitational pull. The solutions clarify acceleration due to gravity, a constant value near the Earth's surface, and its effect on falling objects. Understanding these concepts is crucial for comprehending planetary motion, the weight of objects, and various phenomena in the universe. The NCERT Solutions provide clear explanations and step-by-step problem-solving approaches to help students master this important topic and excel in their exams.

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Quick info

BoardCBSE
ClassClass 9
SubjectScience
Session2026
LanguageEnglish
TypeNCERT Solutions
ChapterChapter 10

Chapter summary

Chapter 10 NCERT Solutions for Class 9 Science explains the fundamental concepts of Gravitation. It details the Universal Law of Gravitation, including its mathematical formula and the gravitational constant. The solutions also cover the phenomenon of free fall and define acceleration due to gravity, providing its standard value. This chapter is crucial for understanding the forces that govern celestial bodies and objects on Earth.

Learning outcomes

  • Understand the Universal Law of Gravitation and its formula.
  • Define and explain the concept of gravitational force.
  • Identify the factors affecting gravitational force.
  • Explain the meaning of free fall.
  • Define acceleration due to gravity and state its value.

Topics covered

Paper topics

  • Universal Law of Gravitation
  • Gravitational Force
  • Mass
  • Distance
  • Gravitational Constant (G)
  • Free Fall
  • Acceleration due to Gravity (g)

Important topics

  • Universal Law of Gravitation
  • Formula for Gravitational Force
  • Concept of Free Fall
  • Acceleration due to Gravity

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Questions and Solutions

Question 1

State the universal law of gravitation.
Solution: The universal law of gravitation states that every object in the universe attracts every other object with a force. This gravitational force is directly proportional to the product of the masses of the two objects and inversely proportional to the square of the distance between their centers. Mathematically, if two objects have masses m_1 and m_2, and the distance between their centers is r, the magnitude of the gravitational force F acting between them is given by the formula:

F = \frac{Gm_1m_2}{r^2}

Here, G is the universal gravitation constant, and its accepted value is approximately 6.67 \times 10^{-11} Nm^2 kg^{-2}.

Question 2

Write the formula to find the magnitude of the gravitational force between the earth and an object on the surface of the earth.
Solution: Let M_E represent the mass of the Earth and m represent the mass of an object situated on its surface. If R denotes the radius of the Earth, then according to the universal law of gravitation, the magnitude of the gravitational force (F) exerted between the Earth and the object can be expressed by the following formula:

F = \frac{GM_Em}{R^2}

In this formula, G is the universal gravitation constant, M_E is the mass of the Earth, m is the mass of the object, and R is the radius of the Earth.

Question 1

What do you mean by free fall?
Solution: Free fall is the motion that occurs when an object is falling towards the center of the Earth solely under the influence of Earth's gravitational force. When an object is released from a certain height, it accelerates downwards due to gravity. This state of motion, where gravity is the only significant force acting on the object (neglecting air resistance), is termed as free fall.

Question 2

What do you mean by acceleration due to gravity?
Solution: Acceleration due to gravity is the acceleration experienced by an object as it falls towards the Earth's surface. When an object is in free fall, its velocity changes continuously due to the Earth's gravitational pull. This rate of change of velocity is known as acceleration due to gravity, denoted by g. The standard value of acceleration due to gravity near the Earth's surface is approximately 9.8 \, m/s^2.

Common mistakes

  • Confusing inverse square law with direct proportionality.
  • Incorrectly applying the formula for gravitational force.
  • Not distinguishing between gravitational force and acceleration due to gravity.

Revision tips

  • Memorize the Universal Law of Gravitation and its formula.
  • Understand the relationship between force, mass, and distance.
  • Clearly differentiate between free fall and other types of motion.
  • Practice problems involving gravitational force and acceleration due to gravity.

Practice MCQs

Q1. What does the Universal Law of Gravitation state about the force between two objects?

Q2. What is the value of the universal gravitation constant (G)?

Q3. What is free fall?

Q4. What is acceleration due to gravity?

Frequently asked questions

What is the Universal Law of Gravitation?

The Universal Law of Gravitation states that every object in the universe attracts every other object with a force that is directly proportional to the product of their masses and inversely proportional to the square of the distance between their centers.

What is the formula for gravitational force?

The formula is F = (G * m1 * m2) / r^2, where F is the gravitational force, G is the universal gravitation constant, m1 and m2 are the masses of the two objects, and r is the distance between their centers.

What is meant by free fall in Class 9 Science?

Free fall refers to the motion of an object when it is allowed to fall towards the Earth solely under the influence of gravity, without any other significant forces acting upon it.

What is acceleration due to gravity?

Acceleration due to gravity (g) is the constant acceleration with which an object falls towards the Earth's center due to gravitational force. Its approximate value is 9.8 m/s^2.

How do these NCERT solutions help with exam revision?

These solutions provide clear, step-by-step explanations of key concepts like the Universal Law of Gravitation and free fall, helping students understand the underlying principles and formulas for effective revision.

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