Case Study:

When engineers launch satellites like INSAT into space, they do not simply place them above Earth - they give them a precise horizontal velocity. Scientists observed that a satellite at an altitude of about 36,000 km completes one revolution in 24 hours, matching Earth’s rotation. Despite being continuously pulled toward Earth due to gravitational force, the satellite does not fall back. Instead, it keeps moving in a curved path around the planet.

If you’ve ever wondered about the fundamental pull of gravity and why objects fall to the ground in the first place, it helps set the stage for understanding these complex orbits.

This phenomenon can be explained using the Universal Law of Gravitation and circular motion.

To master the math behind this, check out our interactive guide to the Universal Law of Gravitation, which simplifies the formulas used by NASA engineers.

Earth’s gravitational force acts as the centripetal force, constantly pulling the satellite toward its center. At the same time, the satellite’s high tangential velocity ensures it keeps moving forward. The balance between gravitational pull and forward motion results in a stable orbit.

If the velocity of the satellite decreases, it may spiral inward and fall toward Earth.

This inward spiral is essentially a form of free fall and acceleration that occurs when forward momentum can no longer fight the pull of the planet.

Conversely, if its velocity increases beyond a certain limit, it may escape Earth’s gravitational field. Thus, maintaining the correct balance of forces is crucial for orbital motion.

Deep Dive:  Now that you know how satellites stay up, find out what life is like inside them - do astronauts really float in space or is something else at play?

CASE-BASED QUESTIONS

MCQ

Q1. Which force keeps the satellite in its circular orbit around Earth?
A. Magnetic force
B. Gravitational force
C. Frictional force
D. Electrostatic force

Q2. If the velocity of a satellite is suddenly reduced, what will most likely happen?
A. It will move into a higher orbit
B. It will escape into space
C. It will move closer to Earth
D. It will stop instantly

Assertion - Reason

Q3. Assertion (A): A satellite remains in orbit because gravitational force acts as centripetal force.
Reason (R): Centripetal force always acts away from the center of circular motion.

Options:
A. Both A and R are true, and R is correct explanation
B. Both A and R are true, but R is not correct explanation
C. A is true, R is false
D. A is false, R is true

Application-Based

Q4. Explain why satellites do not fall directly onto Earth even though gravity is acting on them continuously.

Q5. What would happen if Earth suddenly lost its gravitational force acting on a satellite? Explain the motion of the satellite.

Data/Logic-Based

Q6. A satellite is orbiting Earth with constant speed. If the gravitational force suddenly increases while velocity remains unchanged, predict the change in its orbit and justify your answer.

ANSWER KEY WITH EXPLANATION

A1. B - Gravitational force
Explanation: According to NCERT, Earth’s gravitational force provides the centripetal force needed for circular motion.

A2. C - It will move closer to Earth
Explanation: Reduced velocity decreases the required centripetal balance, causing the satellite to spiral inward.

A3. C - A is true, R is false
Explanation: Gravitational force acts as centripetal force (true), but centripetal force acts toward the center, not away.

A4. Explanation: The satellite has high tangential velocity, so while gravity pulls it inward, it keeps missing Earth, resulting in orbit.

A5. Explanation: Without gravity, no centripetal force acts, so the satellite moves in a straight line due to inertia.

A6. Explanation: Increased gravitational force increases centripetal force, causing the satellite to move into a smaller orbit (closer to Earth).

Ready to ace your Physics exam?  Practice makes perfect. Download our Class 9 Physics Worksheets to sharpen your skills, or test yourself under exam conditions with our Solved and Unsolved Practice Papers.

HOTS EXTENSION QUESTIONS

1. If a satellite is moved to a higher orbit, what changes must be made to its velocity and why?

2. Can a satellite remain stationary relative to Earth without any motion? Justify using physics principles.

Still curious? Post your toughest physics doubts on our Discuss Forum or challenge your friends to a Quick Physics Quiz to see who truly rules the laws of motion!

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