The Earth’s shape and the concept of gravitation are fundamental topics in science. Understanding these concepts is essential for students preparing for the All India Sainik Schools Entrance Examination (AISSEE). Below are important questions and answers to help students grasp these topics effectively.
Shape of Earth and Gravitation (Basic Concepts) for Class 6 & 7
Q&A Format for AISSEE Preparation
1. What is the shape of the Earth?
The Earth is geoid in shape, which means it is slightly flattened at the poles and bulging at the equator. It is not a perfect sphere.
2. How do we know that the Earth is round?
We know that the Earth is round due to:
- The way ships disappear from the bottom up when they go far into the sea.
- The circular shadow of the Earth seen on the Moon during a lunar eclipse.
- The images taken from space show the Earth as a sphere.
3. What is gravity?
Gravity is the force of attraction exerted by the Earth on objects. It pulls everything towards the center of the Earth.
4. Who discovered gravity and how?
Gravity was discovered by Sir Isaac Newton when he observed an apple falling from a tree. He concluded that a force must be pulling it down.
5. Why don’t we float in the air like astronauts in space?
We don’t float in the air because Earth’s gravitational force pulls everything towards its surface. Astronauts experience weightlessness in space due to the absence of significant gravitational pull.
6. What would happen if there was no gravity?
If there were no gravity:
- Everything would float in the air.
- There would be no atmosphere, making life impossible.
- Objects would not stay on the ground.
7. Does gravity act only on Earth?
No, gravity acts on all objects in the universe. Every object with mass exerts a gravitational pull, including the Sun, Moon, and planets.
8. Why do objects fall towards the ground when dropped?
Objects fall because the Earth’s gravitational force attracts them towards its center.
9. Why do astronauts feel weightless in space?
Astronauts feel weightless because they are in a state of free fall around the Earth, experiencing microgravity.
10. What is the difference between mass and weight?
- Mass is the amount of matter in an object and remains constant everywhere.
- Weight is the force of gravity on an object and can change depending on the gravitational force.
11. How does the Moon’s gravity compare to Earth’s?
The Moon’s gravity is 1/6th of Earth’s gravity, which is why astronauts can jump higher on the Moon.
12. What is the role of gravity in keeping planets in orbit?
Gravity keeps planets in orbit around the Sun and moons in orbit around planets. Without gravity, planets would move in a straight line instead of orbiting.
13. What is the center of gravity?
The center of gravity is the point where the entire weight of an object appears to be concentrated.
14. How does gravity affect tides?
The gravitational pull of the Moon and the Sun causes the rising and falling of ocean tides on Earth.
15. Why do heavier and lighter objects fall at the same rate in a vacuum?
In the absence of air resistance, gravity accelerates all objects equally, regardless of their mass.
16. What happens to gravity as we move away from Earth’s surface?
Gravity decreases as we move farther from the Earth’s surface because gravitational force depends on distance.
17. How does Earth’s rotation affect its shape?
Earth’s rotation causes a bulge at the equator and flattening at the poles, making it a geoid rather than a perfect sphere.
18. How do artificial satellites stay in orbit?
Satellites stay in orbit due to a balance between their forward motion and Earth’s gravitational pull.
19. What is weightlessness?
Weightlessness is the condition in which a person or object appears to be floating due to free fall, such as in space.
20. How does gravity help in everyday life?
Gravity helps in:
- Keeping us on the ground.
- Holding the atmosphere in place.
- Enabling objects to stay in place and not float away.
- Allowing rivers to flow and rain to fall.
Q.21 Difference Between Mass and Weight
| Feature | Mass | Weight |
|---|---|---|
| Definition | The amount of matter in an object. | The force exerted by gravity on an object. |
| Symbol | Represented by ‘m’. | Represented by ‘W’. |
| SI Unit | Kilogram (kg). | Newton (N). |
| Constant or Variable? | Remains constant everywhere. | Changes with location (e.g., on the Moon, it is less). |
| Formula | Mass is intrinsic and does not require a formula. | Weight = Mass × Gravitational acceleration (W = mg). |
| Measured By | A beam balance. | A spring balance. |
| Example | A person has a mass of 60 kg on Earth, Moon, and Mars. | The same person’s weight is different on Earth, Moon, and Mars because gravity varies. |
Interesting Facts About Gravity
✔ The Sun’s gravity is 28 times stronger than Earth’s gravity.
✔ Jupiter has the strongest gravity among all planets in our solar system.
✔ The force of gravity is weaker on higher altitudes, such as on mountains.
✔ Black holes have extreme gravity that even light cannot escape.
✔ Without gravity, our bones would weaken, and muscles would shrink over time.
Quick Revision Points:
✔ The Earth is geoid in shape.
✔ Gravity is the force that pulls objects toward the Earth.
✔ Sir Isaac Newton discovered gravity.
✔ The Moon has lower gravity than Earth.
✔ Gravity helps keep planets in orbit.
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