Lecture 6

Question 1

What is 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 centres

F=GMM/r^2

Question 2

What are the two types of orbits?

Answer 2

Bound: ellipses
Unbound: parabolic, hyperbolic

Question 3

What is the centre of mass?

Answer 3

The averaged centre where all mass is distributed. As momentum is conserved, orbiting objects orbit around their centre of mass.

Question 4

What is Newton’s version of Kepler’s third law?

Answer 4

p^2= a^3 4pi^2 /g(M+M)

Question 5

Why is Kepler’s third law important?

Answer 5

Allows us to weigh distant objects

Question 6

2-body problem

Answer 6

Total orbital energy stays constant if there is no external force

Question 7

What makes an orbit change?

Answer 7

-Friction or atmospheric drag
-A gravitational encounter

Question 8

What is escape velocity?

Answer 8

If an object has enough orbital velocity it can escape from a bound orbit to an unbound orbit

Question 9

How does gravity cause tides?

Answer 9

-The moon’s gravity pulls harder on the side of the Earth nearest to the moon
-The difference in the moon’s gravitational pull stretches the Earth

Question 10

What is tidal friction? How does it affect the Moon and the Earth?

Answer 10

Tidal friction gradually slows the Earth’s rotation and makes the moon move farther from the Earth.

Question 11

Why do objects fall at the same rate (equation)?

Answer 11

a(object)= GM(earth)/r^2
The mass of an object in Newton’s second law exactly cancels mass in the law of gravitation