Students can go through AP Inter 1st Year Physics Notes 9th Lesson Gravitation will help students in revising the entire concepts quickly.

## AP Inter 1st Year Physics Notes 9th Lesson Gravitation

→ There are four basic forces in nature, they are

a) Gravitational force

b) Electromagnetic force

c) Strong nuclear force

d) Weak nuclear force

→ Newton’s Universal Law of Gravitation : Every particle of matter in the universe attracts every other particle with a force directly proportional to the product of their masses and inversely proportional to the square of the distance between their centres.

F ∝ \(\frac{\mathrm{m}_1 \mathrm{~m}_2}{\mathrm{~d}^2}\); F = \(\frac{\mathrm{Gm}_1 \mathrm{~m}_2}{\mathrm{~d}^2}\)

→ Gravitational field : A mass particle modifies space around it in some way and through which it interacts with other mass particles.

→ Gravitational field travels with speed of light in vacuum.

→ Black hole is dense object into which other objects could fall but out of which no object or even light could ever come out.

→ A non-accelerating frame is called inertial frame of refer-enceAn accelerating frame is called non-inertial frame of reference.

→ Inertial mass (m_{1}) of an object and its gravitational mass (mg) are equal.

→ On the basis of principle of equivalence, the gravitational and inertial masses are equal.

→ Acceleration due to gravity at a height h

g_{h} = \(\frac{G M}{(R+h)^2}\) = g(1 – \(\frac{\mathrm{2h}}{\mathrm{R}}\))

→ The value of decreases with depth g_{d} = g(1 – \(\frac{\mathrm{d}}{\mathrm{R}}\))

→ The variation of g with latitude of the place on earth g_{Φ} = g – Rw^{2} cos^{2} Φ.

→ ‘g’ value vary with latitude due to non-spherical nature of the earth.

→ Due to local conditions also the value of g will vary from place to place on the surface of the earth.

→ The orbital velocity of a projected body is the velocity with which it revolves in the orbit.

v_{0} = \(\sqrt{\mathrm{gR}}=\sqrt{\frac{\mathrm{GM}}{\mathrm{R}}}\) = 7.92 kms^{-1}

→ The escape velocity of a body is the minimum velocity that should be given in order that it may overcome the earth’s attraction and go into the space.

v_{e} = \(\sqrt{2 \mathrm{gR}}=\sqrt{\frac{2 \mathrm{GM}}{\mathrm{R}}}\) = 11.2 kms^{-1}

→ The escape velocity of a satellite from an orbit is \(\sqrt{2}\) times the orbital velocity.

→ The geostationary satellites are in specified orbits at a height of about 36,000 km above the earth.

→ Law of orbits : All planets move in ellipitcal orbits with the sun situated at one of the foci.

→ Law of areas: The line that joins any planet to the sun sweeps equal areas in equal internals of time.

→ Law of periods : The square of the time period of revolution of a planet is proportional to the cube of the semi-major axis of the ellipse tracedout by the planet

T^{2} ∝ R^{3}

→ The gravitational potential energy is given by

V = \(\frac{-\mathrm{Gm}_1 \mathrm{~m}_2}{\mathrm{r}}\)

→ Time period of polar satellites is 100 minutes.

→ Polar satellites are low altitude satellites, but they go around the poles of the earth in a north- south direction.