WACE Physics — Unit 3
Kepler's Laws — Flashcards & Quiz
Kepler's three laws describe the motion of planets and satellites and can be derived from Newton's law of universal gravitation applied to circular or elliptical orbits. WACE Physics Year 12 Unit 3 expects you to state and apply each law and to derive Kepler's third law (T² ∝ r³) from the condition that gravity provides centripetal force.
Sample Flashcards
Q1: State Kepler's three laws.
1st: Planets orbit in ellipses with the Sun at one focus. 2nd: Equal areas swept in equal times. 3rd: T² ∝ r³ for bodies orbiting the same central mass.
Q2: How does Kepler's 2nd law relate to angular momentum conservation?
Gravity is radial (no torque), so L = mvr is conserved. When r decreases, v increases — producing equal-area sweeping.
Sample Quiz Questions
Q1: Kepler's first law says planets orbit in perfect circles.
Answer: FALSE
Orbits are ellipses with the Sun at one focus.
Q2: A planet moves faster when closer to the Sun.
Answer: TRUE
Equal areas in equal times requires greater speed at shorter radius.
Q3: T²/r³ is the same for objects orbiting different central bodies.
Answer: FALSE
The constant depends on the central body's mass M.
Last updated: March 2026 · 2 flashcards · 3 quiz questions