Gravitation Class 9 Important Questions | Free PDF Download

Gravitation is basically the concept in physics based on which the attractive force between two objects is described as related to their masses. It is one of the forces of nature, affecting everything from planets in motion to objects on Earth. Gravitation is studied in class 9 as part of the science syllabus and is thus considered very important to establish a firm base in the subject of physics. 

This article will address some Class 9 extra questions on gravitation that will help students gain a deeper understanding of the subject. Gravitation Important Questions Class 9 contains various topics that are asked every year in class 9 final examinations. In this chapter, you will understand about the universal law of gravitation, acceleration due to gravity, escape velocity, gravitational potential energy, etc. 

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Important Questions On Gravitation

This section will cover some of the extra questions on the Class 9 physics chapter, Gravitation.

Explain the concept of gravitation and its significance in nature.

Gravitation is the force that attracts any two objects that possess mass. It is one of the basic forces of nature that acts on all objects regardless of their size. This force causes attraction between two objects. There are two primary factors on which the strength of gravitation depends. These are:

• Masses of objects: The stronger the masses, the stronger the gravitational force of attraction.
• The distance between the objects: If objects are close to each other, then attraction is high, and if they are separated, then force decreases.

How Does Gravity Affect the Motion of Planets?

Gravity is the force that keeps the planets in orbits around the sun. The force of gravity attracts the planets toward the sun, but the inertia makes the planets want to move in a straight line. Since the Sun is gravitating around them, however, planets constantly curve their routes, which eventually makes them trace elliptical paths instead of linear paths.

This interplay between a planet's inertia, which would push it to move straight, and the Sun's gravitational force, which pulls it inward, creates planetary orbits. The concept behind this is derived from Newton's law of gravitation and the law of inertia.

Define free fall. What is the acceleration experienced by an object in free fall near the Earth's surface?

Free fall means a motion when a body experiences the influence of gravity without any opposing forces, for instance, resistance offered by the atmosphere. Thus, an object will accelerate downwards from the earth's surface at a constant speed due to gravitational force during its free fall motion. Such a constant acceleration has been known by the term acceleration due to gravity, and the constant value that usually represents such a quantity in space near the earth's surface is around 9.8 m/s².

All objects fall at the same rate if we ignore air resistance in free fall. Galileo showed this by dropping two spheres of different weights from the Leaning Tower of Pisa. He observed that they hit the ground simultaneously.

What is the Difference Between Mass and Weight?

Mass and weight are two different concepts:

• Mass is the amount of matter contained in an object and never changes with where the object is. It’s measured in kilograms.
• Weight is the force of gravity on an object. Its amount depends on how massive the object is and also on how strong the gravitational acceleration is. The unit of weight is newtons, N.

For instance, on the Moon, the gravitational acceleration g is about 1/6th that of Earth. Hence, the weight of an object would significantly be less on the Moon while the mass is maintained to be the same.

Why Do Astronauts Appear Weightless in Space?

Astronauts seem to be weightless in space because they are actually in free fall as they orbit the Earth. Gravity is acting on them, but they are always falling toward the planet. Because of their high forward velocity, they never actually hit the Earth. It is this free fall that gives the impression of weightlessness. The term microgravity is used to describe the nearly gravity-free environment that exists in orbit.

How Does Gravity Affect the Tides?

The gravitational forces of the Moon and the Sun affect the tides on Earth. The bulge in the oceans created by the gravitational force of the Moon results in high tides on the side of Earth facing the Moon. Another high tide is also felt on the opposite side due to the centrifugal force developed by the rotation of the Earth-Moon system. The Sun also contributes to the generation of tides, but compared to the Moon, it is not as efficient in generating tides.

What is the Concept of Escape Velocity?

Escape velocity is the minimum speed at which an object leaves the gravitational influence of a planet or some other celestial body. For instance, on Earth, the escape velocity is approximately 11.2 km/s. That is the velocity at which an object is projected vertically upwards from Earth such that it does not come back.

Why is the value of 'g' slightly less at the poles than at the equator?

The value of g is a little lower at the poles because the earth is not spherical in shape but is actually an oblate spheroid. This means that the Earth is slightly flattened at the poles and bulges at the equator. So, the distance from the centre of the Earth is greater at the equator, and hence the gravitational pull is weaker there.

What is the effect of gravity on a satellite in orbit?

Gravity holds the satellite in orbit around Earth. The satellite is always falling toward the Earth due to gravity, but because it travels forward at a very high speed, it constantly misses the planet. It is this balance between the forward movement of the satellite and the gravitational pull that keeps it in orbit.

State and explain Newton’s Law of Universal Gravitation.

Newton's Law of Universal Gravitation states that any two objects in the universe attract each other with a force proportional to their masses and inversely proportional to the distance between them. Its formula is this:

F = G × m₁ × m₂ / r²

Where:

• F represents the gravitational force between the two objects.
• G is the gravitational constant, approximately 6.674 x 10^-11 Nm² / kg².
• Let the masses of two objects be denoted as m1 and m2.
• And r is the distance between two objects separating the centres of these objects.

This law provides insight into how gravity operates on all levels, from the movement of planets to the attraction between everyday items. Gravitation is one of the fundamental forces in the universe. It serves not only to keep planets in orbit but can also be interpreted in understanding the behaviours of objects upon Earth. An understanding of principles such as weight, free fall, escape velocity, and the law of universal gravitation gives students an insightful understanding of both the small and big-scale effects of gravity. Mastering these principles is very essential to physics students and will lay the foundation for further studies on more complex topics in science and astronomy. We hope that you practice the above Important Questions of Gravitation Class 9 and achieve your dream marks. All the Best