PreScreener: Orbital Motion

Task 1: Force and Distance

The diagram below shows a planet orbiting a star. Position A is closest to the star, and Position B is furthest away.

1. At which position is the gravitational force between the star and the planet the STRONGEST?
   • ( ) Position A (Perihelion)
   • ( ) Position B (Aphelion)
   • ( ) The force is the same at both positions.
2. Explain your reasoning: ______

Task 2: Kepler’s Observations

Match the description to the correct Law of Planetary Motion.

• Kepler’s 1st Law: ______
• Kepler’s 2nd Law (Equal Areas): ______
• Kepler’s 3rd Law (Harmonic Law): ______

Options: A) A planet sweeps out equal areas in equal times (velocity changes). B) Orbits are ellipses with the Sun at one focus. C) The square of the period is proportional to the cube of the distance.

Task 3: Predicting Motion

If a planet’s orbit is a perfect circle (Eccentricity = 0), will its orbital velocity change as it moves around the Sun? Why or why not?

(Space for student response)