Kepler's Laws Of Planetary Motions
TECTechnics Classroom   TECTechnics Overview

Kepler's Laws Of Planetary Motions

planet A revolves around the Sun, S (figure 122.1):
(a) Describe its path around the sun.
(b) Is the velocity of A constant throughout its revolution around the sun?
(c) Relate the period of A's revolution to its mean distance from the sun.

The strings: S7P4A42 (Motion - Rotation).

The math:
Pj Problem of Interest is of type motion (rotation).

(a) A's path is elliptic.
Kepler's First Law: each planet moves on an ellipse and the sun is at one focus.

(b) No. Planet A does not move at constant velocity around the sun. It moves faster when closer to the sun. This is a consequence of Kepler's second law.
Kepler's Second Law: a line drawn from the sun to the planet sweeps out equal areas in equal times. Area ABS is equal to area SCD in equal times (figure122.1). So arc CD is longer than arc AB.

(c) If T is the period of revolution of any planet around the sun and D is its mean distance from the sun, then:
T2 = kD3.
Where T is period of revolution
k is a constant and is the same for all the planets.
D is the mean distance from the sun.

Blessed are they that have not seen, and yet have believed. John 20:29