CBSE Class 11 Physics Gravitation Notes Set 03

Class XI: Physics

Chapter 8: Gravitation

Chapter Notes

Key Learnings:

1. Newton’s law of universal gravitation states that the gravitational force of attraction between any two particles of masses m₁ and m₂ separated by a distance r has the magnitude F=G m₁m₂/r₂ Where G, the universal gravitational constant, has the value 6.672 x 10^-11 Nm² kg-².

2. From the principle of superposition each force acts independently and uninfluenced by the other bodies. The resultant force FR is then found by vector addition.

3. For small heights h above the earth’s surface the value of g decreases by a factor (1-2h/R).

4. The gravitational potential energy of two masses separated by a distance r is inversely proportional to r.

5. The potential energy is never positive; it is zero only when the two bodies are infinitely far apart.

6. The gravitational potential energy associated with two particles separated by a distance r is given by
V=-GM₁M₂/r  Where V is taken to be zero at r→ ∞. 

7. The total mechanical energy is the sum of the kinetic and potential energies. The total energy is a constant of motion.

8. If an isolated system consists of a particle of mass m mobbing with a speed v in the vicinity of a massive body of mass M, the total mechanical energy of the particle is given by E=1/2mv²-GMm/r.

If m moves in circular orbit of radius a about M, where M >> m, the total energy of the system is E=-GMm/2a.

9. The escape speed from the surface of the Earth isve=√2GM_E/R_{E =}√2gR_E And has a value of 11.2 km s^-1.

10. Kepler’s law of planetary motion:

i. The orbit of the planet is elliptical with sun at one of the focus - LAW OF ORBITS.

ii. The line joining the planet to the sun sweeps out equal area in equal interval of time - LAW OF AREAS.

iii. The square of the planet’s time period of revolution T, is proportional to the cube of semi major axis a.

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