2. Kepler’s Laws of Planetary
Motion
#) 1st Law :Law of Orbits(1609)
#) 2nd Law :Law of Areas(1609)
#)3rd Law :Law of Periods(1618)
3. 1 st Law : Law of gravitation
All planets moves in elliptical orbits with the sun
situated at one of the foci.
4. 2 Law :Law of areas
nd
Line that joins any planet to the sun sweeps
equal areas in equal intervals of time.
5. 3 Law : Law of
Periods
rd
The square of the period of revolution of a planet
around the sun is proportional to cube of semi
major axis of its eclipse.
6. Universal law of
Gravitation
Every body in the universe attracts every other body
with a force directly proportional to the product of the
two masses and inversely proportional to the square of
their distance.
7. Acceleration due to Gravity (g)
Assume that the earth is spherical. Let mass be M and
radius be R. Consider a body of mass m lying on the
surface of the earth.
According to Newton,
F = G m m /R x R---------------(1)
But
F = mg------------------(2)
From(1)&(2)
mg = G M m/ R x R
g = G M /R x R
