Watch Video
An Overview of Ncert Books Class 9 Science Chapter 10 Free Download
Ncert Books Class 9 Science Chapter 10 Free Download
ShareShare
FAQs on Ncert Books Class 9 Science Chapter 10 Free Download
1. What types of numerical problems from Chapter 10, Gravitation, are important for the Class 9 exam?
For the CBSE Class 9 exam 2025-26, you should focus on numericals based on:
Calculating the gravitational force between two objects using the Universal Law of Gravitation formula, F = G(Mm/d²).
Problems involving free fall, using equations of motion (v = u + gt, s = ut + ½gt², v² = u² + 2gs).
Calculating the weight of an object on Earth and the Moon (W = mg).
Problems on Thrust and Pressure (P = F/A).
Calculating relative density. These are frequently asked in 3-mark questions.
2. Differentiate between Mass and Weight. Why is this a frequently asked question in exams?
This is a key conceptual question, often carrying 2 or 3 marks. The main differences are:
Mass is the measure of the amount of matter in an object. Its SI unit is the kilogram (kg). It is a scalar quantity and remains constant everywhere.
Weight is the gravitational force exerted on an object. Its SI unit is the Newton (N). It is a vector quantity (W = mg) and its value changes depending on the acceleration due to gravity (g).
3. State the Universal Law of Gravitation and explain why it is important for your exams.
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. The mathematical expression is F = G(Mm/d²). This law is considered very important as it explains several key phenomena, including:
The force that binds us to the Earth.
The motion of the Moon around the Earth and planets around the Sun.
The formation of tides.
4. How is 'g' (acceleration due to gravity) different from 'G' (Universal Gravitational Constant)?
This is a crucial distinction often tested in exams. The key differences are:
'g' (acceleration due to gravity) is the acceleration gained by an object due to gravitational force. Its value varies depending on the location (e.g., approx. 9.8 m/s² on Earth's surface) and is not constant throughout the universe.
'G' (Universal Gravitational Constant) is the constant of proportionality in the gravitation formula. Its value is 6.673 × 10⁻¹¹ Nm²/kg² and is the same everywhere in the universe.
5. Why does an object weigh six times less on the Moon compared to the Earth?
This is a classic application-based question. An object's weight is the product of its mass and the acceleration due to gravity (W = mg). While the mass of an object is constant everywhere, the acceleration due to gravity on the Moon (g_moon) is approximately 1/6th of the acceleration due to gravity on Earth (g_earth). This is because the Moon's mass and radius are much smaller than Earth's, resulting in a weaker gravitational pull. Therefore, the object's weight on the Moon is one-sixth of its weight on Earth.
6. Explain Archimedes' Principle. How is this concept typically tested in a 3-mark or 5-mark question?
Archimedes' Principle states that when an object is immersed fully or partially in a fluid, it experiences an upward force, called buoyant force, which is equal to the weight of the fluid it displaces. For exams, this is often tested through:
Conceptual Questions (3 marks): Asking why a heavy ship made of iron floats while a small iron nail sinks.
HOTS Questions (5 marks): Numerical problems to calculate buoyant force and predict if an object will sink or float based on its density relative to the fluid's density.
7. If the distance between two objects is reduced to half, how is the gravitational force between them affected?
This is a common higher-order thinking question. According to the Universal Law of Gravitation, force (F) is inversely proportional to the square of the distance (d²), i.e., F ∝ 1/d². If the distance 'd' is halved (d/2), the new force (F') will be proportional to 1/(d/2)². This simplifies to 1/(d²/4) or 4/d². Therefore, the new gravitational force will become four times the original force.
8. From an examination perspective, explain why school bags have wide straps.
This question tests the practical application of the concept of pressure. Pressure is defined as force applied per unit area (P = F/A). The weight of the bag creates a downward force. By using wide straps, the surface area over which this force is distributed increases. Since pressure is inversely proportional to area, a larger area results in less pressure on the shoulders, making it more comfortable to carry. This is an expected application-based question.
9. In a vacuum, if a 1 kg iron ball and a feather are dropped from the same height, which will reach the ground first? Justify your answer.
In a vacuum, where there is no air resistance, both the iron ball and the feather will reach the ground at the exact same time. This is a very important concept for exams. The justification is that the acceleration due to gravity (g) is independent of the mass of the falling object. Both objects accelerate downwards at the same rate, covering the same distance in the same time interval.
10. What kind of objective or Multiple Choice Questions (MCQs) are expected from the Gravitation chapter?
For the Class 9 Science exam, important MCQs often focus on:
The SI units of G, g, pressure, and weight.
The constant value of 'G' and the standard value of 'g' on Earth.
The relationship between gravitational force and distance (e.g., if distance triples, force becomes 1/9th).
The location where the value of 'g' is maximum (at the poles) or minimum (at the equator).
The factors on which buoyant force depends, such as the volume of the object immersed and the density of the fluid.
