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UPPCS Physics Gap Sheet: Motion, Forces and Gravity.
UPPCS has asked 18 of these. 10 have not been asked yet. Lock the first list, then read the second: it holds what UPPCS has not used yet.
First, the concept
A force can change motion. Inertia resists that change, while momentum is conserved in an isolated system. Action and reaction act on different bodies, so they do not cancel on one body.
Mass measures inertia and does not change with location. Weight depends on gravity. Orbiting astronauts feel weightless because they and their spacecraft fall together, even though Earth still attracts them.
✅ Already asked (18)
Motion and conservation
- Starting bus and inertia · A passenger leans backward when a bus starts because the body tends to remain at rest.
- Sudden braking · A passenger lurches forward because the body tends to keep moving.
- Rocket propulsion · Expelled gas carries momentum backward; the rocket gains forward momentum, even in vacuum.
- Walking on a boat · The boat moves oppositely when a person walks on it, if external horizontal forces are negligible.
- Recoil of a gun · The gun recoils opposite to the bullet because total momentum is conserved.
- Circular motion · A force towards the centre continually changes the direction of velocity.
- Moving wind and energy · Wind turbines use the kinetic energy of moving air.
Gravity and space
- Mass on Earth and Moon · Mass remains the same; weight on the Moon is about one-sixth of Earth weight.
- Weight at poles · For the same body, weight is generally greater at the poles than at the equator.
- Orbital weightlessness · An orbiting spacecraft and its contents are in continuous free fall.
- At the top of a vertical throw · Velocity is momentarily zero, but gravitational acceleration is still downward.
- Geostationary satellite · A circular equatorial orbit in Earth's rotation direction makes it appear fixed above one longitude.
Friction and stability
- Starting a loaded cart · Maximum static friction is usually greater than sliding friction.
- Walking on ice · Low friction gives the feet less grip.
- Wide base and balance · A body remains stable when the vertical through its centre of gravity falls within its base.
Further everyday mechanics
- Newton's third law · Equal and opposite action and reaction forces act on different bodies.
- Accelerating train and tossed coin · A vertically tossed coin can land behind the thrower when the train accelerates forward.
- Skater pulling arms inward · Rotation speeds up when moment of inertia decreases and external torque is negligible.
❌ Not asked yet (10)
Items marked 'asked in other exams' have come in UPSC or other state exams, not yet in UPPCS.
🔒 10 items not asked yet
Gravity and space: 2 · Friction and stability: 3 · Further everyday mechanics: 5
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⚠️ Uniform circular motion has constant speed but changing velocity. Orbital weightlessness is free fall, not absence of gravity.
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