Q. When a man circles round the earth in a satellite, then (UPSC Prelims 1979)
Correct Answer: (b) Mass remains constant but weight becomes zero
Why option (b) is correct?
• Mass is the amount of matter → does not change anywhere
• Weight = m × g → depends on gravitational acceleration (g)
• In a satellite, the astronaut and satellite are in continuous free fall around the Earth
• Normal reaction becomes zero → apparent weight = 0 (Weightlessness)
👉 Gravity is not zero in orbit; the astronaut only appears weightless
• Mass is the amount of matter → does not change anywhere
• Weight = m × g → depends on gravitational acceleration (g)
• In a satellite, the astronaut and satellite are in continuous free fall around the Earth
• Normal reaction becomes zero → apparent weight = 0 (Weightlessness)
👉 Gravity is not zero in orbit; the astronaut only appears weightless
Key Concepts You Must Know
1. Mass vs Weight
• Mass → Independent of location, SI unit: kg
• Weight → Depends on gravity, SI unit: Newton (N)
• In space → Mass same, Weight zero (apparent)
2. What is Weightlessness?
• Condition when apparent weight becomes zero
• Occurs when no supporting force acts on the body
• Seen in satellites, free-falling lift, space stations
3. Why do astronauts float?
• Satellite has tangential (orbital) velocity
• Gravity provides centripetal force
• Astronaut and satellite fall together → no contact force → floating effect
4. Is gravity absent in space?
❌ No
• Gravity decreases with height but never becomes zero
• At satellite height, gravity is about 90% of Earth’s surface value