Class 11 Physics Chapter 7 Gravitation – Revision Notes

Chapter 7 of Class 11 Physics starts from Newton’s law of gravitation and builds up to Kepler’s three laws of planetary motion, the variation of g with height and depth, and escape velocity. It closes with the orbital mechanics behind geostationary satellites.

Last Updated: September 23, 2026

Newton’s Law

• F=Gm1m2/r²; G=6.67×10⁻¹¹ Nm²/kg².

Kepler’s Laws

• 1st: elliptical orbits.
• 2nd: equal areas in equal times.
• 3rd: T²∝r³.

g, Potential Energy, Escape Velocity

• g=GM/R²; decreases with height and depth.
• U=−GMm/r; v_e=√(2gR).

Satellites

• v_o=√(GM/r); geostationary period=24 h.

One-Line Summary

Gravitation describes the universal attractive force between masses, governing planetary orbits (Kepler’s laws), surface gravity, escape velocity, and satellite motion.

Quick visual: a worked diagram from the full Solutions page, for reference.

Frequently Asked Questions

How do the laws of planetary motion given by Kepler relate to the law of gravitation given by Newton?
Kepler described the motion of planets empirically through observation, while the law of gravitation later provided the underlying force explanation, showing the same gravitational force that makes an apple fall also keeps planets in orbit.

Why do astronauts in orbit appear weightless even though gravity is still acting on them?
Astronauts in orbit are in continuous free fall around the Earth. Gravity provides exactly the centripetal force needed to keep them in orbit, so they and their spacecraft fall together, creating the sensation of weightlessness.

Written by Satish

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