# At what point in a planet's elliptical orbit does it move fastest? At what point does it move slowest? At what point does it 'sweep out area' at the fastest rate?

Asked by EgaoNoGenki (1164) February 18th, 2010

(Consider the definitions of aphelion and perihelion, and Kepler’s Laws…)

The possible answers are as follows. When you decide on one, please explain the reasoning behind your choice:

A. It moves with the same speed and sweeps out the same area per unit time at all points on the orbit.

B. It moves with the same speed at all points, and sweeps out area at the fastest rate at perihelion.

C. It moves fastest at perihelion, slowest at aphelion, and sweeps out the same area per unit time at all points on the orbit.

D. It moves fastest at perihelion, slowest at aphelion, and sweeps out area at the fastest rate at perihelion.

E. It moves slowest at perihelion, fastest at aphelion, and sweeps out area at the slowest rate at perihelion.

Observing members: 0 Composing members: 0

Objects moving in elliptical orbits move fastest when they are closest to the central body, and most slowly when they are furthest from the central body. Johannes Kepler realized this and stated it in his Second Law of Planetary Motion.

Fluther frowns upon helping people with homework. However, I will link you to this webpage to play with. See if you can get an instinctive feeling for elliptical orbits by modeling some.

hannahsugs (3238)

C

Ivan (13479)

Thank you, @Ivan. I scanned my textbook to double-check, and after looking hard enough, that was correct.

EgaoNoGenki (1164)

C

talljasperman (21910)

I believe that you already know the answer, fluther is not a pub quiz site.

Odysseus (2751)

or