Transcript Kepler’s Three Laws of Planetary Motion

Kepler’s Three Laws of
Planetary Motion
• http://www.youtube.com/watch?v=lm9EjYMXto
Kepler’s Laws of Planetary Motions
1. Planets move in elliptical orbits with the
sun at one of the foci
SUN
Foci – 2 points that are
equidistant from center
on major axis
cir cle
e llips e
2. Law of Areas
Line from the sun to a planet sweeps with
equal areas in equal time. A planet will
move through equal area of space in an
equal amount of time
Perihelion – closest to sun
Ahelion – farthest from sun
i. When a planet is in perihelion its orbital
velocity increases
ii. When a planet is in aphelion its orbital
velocity decreases
Farthest
from sun
Closest
to sun
Slower
Velocity
Faster
Velocity
Closer to the sun, faster the velocity
because of the gravitational pull.
Greater
Gravitational
Pull
3. Law of Periods - The farther a planet is
from the focus, the longer the period of
revolution.
Ex: Earth is closer to the sun than Jupiter,
therefore the Earth has a shorter period of
revolution. (ESRT)
•
Newton’s Law of Gravity
•
•
•
The force of attraction between any two
objects depends on their masses and the
distance between them.
Thus, the closer the objects, the
greater
______________
the gravitational pull
Thus, the bigger the object the
greater the gravitational pull
__________
Gravity
Force of gravity
Force of gravity
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Month
Closer to the sun in the winter,
farther from sun in summer
• http://astro.unl.edu/naap/pos/animations/k
epler.html