Lecture Six

Question 0

Three types of orbits?

Answer 0

• bound (elliptical)

- unbound (parabola and hyperbola)

Question 1

Newton’s Universal Law of Gravitation?

Answer 1

1. Every mass attracts every other mass.
2. Attraction is directly proportional to the product of their masses.
3. Attraction is inversely proportional to the square of the distance between their centers.

Question 2

Centre of mass and orbits

Answer 2

As momentum is conserved, orbiting objects orbit around their centre of mass.

Question 3

2-body problem

Answer 3

• Total orbital energy (gravitational + kinetic) stays constant if there is no external force.
• Orbits cannot change spontaneously.

Question 4

Changing an orbit

Answer 4

Friction or atmospheric drag or a

gravitational encounter

Question 5

Escape velocity

Answer 5

If an object gains enough orbital energy, it may escape (change from a bound to unbound orbit)