Page 104 - text book form physics kssm 2020

Th e square of the orbital period of any planet is
Kepler’s
directly proportional to the cube of the radius
Th ird Law Mathematically,
of its orbit (Law of Periods). T ∝ r
2
3
T = orbital period of
A planet which orbits with a larger radius has a longer a planet
orbital period. As such, planets which are further from the Sun r = radius of orbit
take a longer time to complete one orbit around the Sun.
For example, the Earth takes 1 year to make one complete
orbit while Saturn takes 29.5 years. Figure 3.27 shows the orbits
and orbital periods of planets.

Neptune
(164.8 years)

U U U U
Uranus
(84.0 years)
S S
Saturnttt
(29.5 years)
Sun
Jupiter
(11.9 years)

Mercury
M M M M M M M
(0.2 years)
Venus
(0.6 years)
Earthtt
E
(1.0 year)
M M M M M
Mars
(1.9 year)

Figure 3.27igure 3.27 Orbits and orbital periods of planets Orbits and orbital periods of planets
F

98 3.2.1
98
3.2.1