Gravity (Earth’s Gravitation) MCQs Quiz | Class 9
This Class IX Science (Code 086) quiz covers Unit III: Motion, Force and Work, specifically focusing on Gravity as the force of the Earth and its direction toward the center. Test your understanding of Earth’s gravitation concepts, submit your answers to see the score, and download the solution PDF for revision.
Understanding Gravity and Earth’s Gravitation
Gravity is a natural phenomenon by which all things with mass or energy are brought toward one another. In the context of Class 9 Science (Unit III), we focus primarily on the gravitational force exerted by the Earth. This force is responsible for holding the atmosphere, keeping us grounded, and governing the motion of the moon around the Earth.
Key Concepts
- Gravitational Force of Earth: The Earth attracts every object towards its center. This force of attraction is called gravity. It is the reason why objects thrown upwards fall back to the ground.
- Direction of Force: The gravitational force always acts towards the center of the Earth. This is why “down” is defined as the direction towards the Earth’s core.
- Universal Law of Gravitation: Every object in the universe attracts every other object with a force that is proportional to the product of their masses and inversely proportional to the square of the distance between them.
- Acceleration due to Gravity (g): When an object falls freely under gravity, it accelerates. Near the Earth’s surface, this value is approximately 9.8 meters per second squared.
| Property | Universal Gravitational Constant (G) | Acceleration due to Gravity (g) |
|---|---|---|
| Value | Constant everywhere in the universe | Changes from place to place |
| Nature | Scalar Quantity | Vector Quantity (directed to center) |
| Unit | Nm squared per kg squared | m per second squared |
Quick Revision Points
- Free Fall: Whenever objects fall towards the Earth under this force alone, we say the objects are in free fall.
- Weight vs Mass: Mass is the quantity of matter (constant), while Weight is the force with which the object is attracted to the Earth (varies with ‘g’).
- Centripetal Force: The gravitational force of the Earth provides the necessary centripetal force for the Moon to orbit around it.
Extra Practice Questions
- 1. If the distance between two objects is tripled, how does the gravitational force change? (Answer: It becomes one-ninth)
- 2. What is the value of ‘G’ accepted universally? (Answer: 6.673 x 10 to the power -11)
- 3. Why does a feather and a stone fall at the same rate in a vacuum? (Answer: Acceleration due to gravity is independent of mass)
- 4. Where is the value of ‘g’ greater: poles or equator? (Answer: Poles)
- 5. What is the weight of an object at the center of the Earth? (Answer: Zero)
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