Week 2 - Gravity & Orbits and Solar system

Question 1

Kepler’s 3 laws

Answer 1

1. Every planet’s orbit is an ellipse with the Sun at one of the two foci
2. A line joining the Sun and a planet sweeps out equal areas in equal times
3. The square of a planet’s orbital period is proportional to the cube of the semi-major axis of its orbit

Question 2

Newton’s three laws of motion

Answer 2

1. An object at rest remains at rest, and an object in motion remains in motion at constant speed and in a straight line unless acted on by an outside force.
2. The acceleration of an object depends on the mass of the object and the amount of force applied.
3. Whenever one object exerts a force on another object, the second object exerts an equal and opposite on the first.

Question 3

Describe and apply the law of Universal Gravitation

Answer 3

Every particle attracts every other particle in the universe with a force that is directly proportional to the product of their masses and inversely proportional to the square of the distance between their centres.

Can be applied to both small and large bodies.

Question 4

Explain the difference between Kepler’s 3rd law and Newton’s version of Kepler’s 3rd law

Answer 4

It includes M1+M2

Question 5

How to calculate centre of mass?

Answer 5

The centre of mass can be calculated by taking the masses you are trying to find the centre of mass between and multiplying them by their positions (you can choose the position - see picture). Then, you add these together and divide that by the sum of all the individual masses.

Question 6

Factors which affect the stability of a planetary orbit within or around a binary system

Answer 6

S-type orbits: depend on the distance ratio between the star and planet, and the stellar companions, in the range of 0.22 and 0.46, depending on the mass ratio.

P-type orbits: the regions of stability also depend on that distance ratio, in the range of 1.75 and 2.45, again depending on the the mass ratio.

Question 7

Explain solar nebula theory

Answer 7

Formation of our solar system from a nebula cloud made from a collection of dust and gas. It is believed that the sun, planets, moons, and asteroids were formed around the same time around 4.5 billion years ago from a nebula.

Question 8

The composition of the primordial solar nebula is thought to be very similar to:

Answer 8

The outer layers of the Sun