CBSE Class 9 Science Chapter 10 Gravitation NCERT Solutions

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NCERT Solutions PDF Class 9 PDF

This chapter delves into the fundamental principles of Gravitation, a key concept in Class 9 Science. The NCERT Solutions provide clear explanations and step-by-step solutions for exercises related to Newton's Universal Law of Gravitation, explaining the force between any two objects in the universe. It also covers the concept of free fall, where an object moves solely under the influence of gravity, and defines acceleration due to gravity, the constant acceleration experienced by objects in free fall near the Earth's surface. These solutions are designed to help students grasp these essential physics concepts, understand the formulas, and prepare effectively for their examinations by offering detailed problem-solving approaches.

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Quick info

BoardCBSE
ClassClass 9
SubjectScience
Session2026
LanguageEnglish
TypeNCERT Solutions
ChapterChapter 10: Gravitation

Chapter summary

Chapter 10: Gravitation NCERT Solutions for Class 9 Science covers the universal law of gravitation, detailing the force between masses. It explains the phenomenon of free fall and defines acceleration due to gravity, including its standard value. The solutions focus on understanding these core concepts and their mathematical representations, aiding students in mastering the basics of gravitational force and motion under gravity.

Learning outcomes

  • Understand the universal law of gravitation and its formula.
  • Define and explain free fall.
  • Define and explain acceleration due to gravity.
  • Apply the universal law of gravitation to calculate gravitational force.
  • Recognize the relationship between Earth's mass, object's mass, and distance in gravitational force calculations.

Topics covered

Paper topics

  • Universal Law of Gravitation
  • Gravitational Force
  • Gravitational Constant (G)
  • Mass of Earth
  • Radius of Earth
  • Free Fall
  • Acceleration due to Gravity (g)
  • Motion under Gravity

Important topics

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

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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, for two objects with masses m_1 and m_2, separated by a distance r, the force of attraction F is given by:

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

Here, G is the universal gravitational constant, with a value of 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 located on its surface. If R is the radius of the Earth, then according to the universal law of gravitation, the magnitude of the gravitational force (F) acting 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 gravitational constant.

Question 1

What do you mean by free fall?
Solution: Free fall is the motion that occurs when an object is allowed to fall towards the Earth's surface solely under the influence of the Earth's gravitational force. When an object is released from a certain height, it accelerates downwards because of gravity, and this state of motion is known as free fall.

Question 2

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

Common mistakes

  • Confusing the universal gravitational constant (G) with acceleration due to gravity (g).
  • Incorrectly applying the inverse square law in calculations.
  • Not distinguishing between mass and weight in gravitational contexts.

Revision tips

  • Memorize the universal law of gravitation and its formula accurately.
  • Understand the difference between 'g' and 'G'.
  • Practice problems involving calculating gravitational force.
  • Clearly define free fall and acceleration due to gravity in your own words.

Practice MCQs

Q1. What does the universal law of gravitation state about the force between two objects?

Q2. What is the formula for the gravitational force between the Earth (mass M_E) and an object (mass m) on its surface (radius R)?

Q3. What is the phenomenon called when an object falls towards the Earth solely under the influence of gravity?

Q4. What is the approximate value of acceleration due to gravity (g) on Earth?

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 gravitational constant, m1 and m2 are the masses of the two objects, and r is the distance between their centers.

What is free fall?

Free fall is the motion of an object where gravity is the only force acting upon it. The object accelerates towards the center of the Earth.

What is acceleration due to gravity?

Acceleration due to gravity (g) is the constant acceleration experienced by an object during free fall. Its standard value near the Earth's surface is approximately 9.8 m/s^2.

What is the value of the universal gravitational constant (G)?

The value of the universal gravitational constant (G) is approximately 6.67 x 10^-11 Nm^2 kg^-2.

How do these solutions help with exam preparation?

These solutions provide clear, step-by-step explanations for key concepts and formulas in Gravitation, helping students understand the principles and practice problem-solving for effective exam revision.

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