Week 2

Question 1

Conservation of energy/mass

Answer 1

Energy cannot be created or destroyed, can change form or be exchanged, total energy content of universe determined in big bang.

Question 2

What is the approximate location of our Solar System in the Milky Way galaxy?

Answer 2

in the outskirts of the galaxy’s disk, about two-thirds of the way out

Question 3

Newtons version of Kepler’s 3rd law

Answer 3

Can be used for anything (not just stuff orbiting the sun)

Question 4

Galaxy order

Answer 4

you, Earth, Solar System, Milky Way, Local Group, Local Supercluster

Question 5

Weight

Answer 5

The net force acting on a body, (including gravity)

Question 6

What causes tides?

Answer 6

Gravity from moon pulling on side of water nearer to it, causing bulges which create tides

Question 7

acceleration

Answer 7

Change in velocity, is affected by gravity

Question 8

What acts against gravity

Answer 8

Air friction

Question 9

Velocity

Answer 9

Speed in a particular direction

Question 10

On a cosmic calendar, if the history of the Universe were compressed into 1 year, how long is a human life span?

Answer 10

The universe is 13.7 billion years old ie 1.4x10^10 years. We live for 10^2 years so we want 10^-8 of a year.

There are 3x10^7 seconds in a year, so the answer is about 0.3 of a second.

Question 11

Gravitational constant

Answer 11

Question 12

Conservation of angular momentum

Answer 12

angular momentum only changes from twisting forces (torque)

= mass x velocity x radius

Question 14

Newton’s first law

Answer 14

An object moves at constant velocity, unless a net force acts to change its speed or direction

Question 15

From Kepler’s third law, a hypothetical planet that is twice as far from the Sun as the Earth, should have a period of

Answer 15

K3L: p^2=a^3

2^3=P²

P=~3

the period should be about 3 earth years

Question 16

Temperature

Answer 16

Average kinetic energy

Question 18

Thermal energy

Answer 18

Sum of kinetic energy

Question 19

Suppose there are 100 billion stars in the Milky Way.

I count the stars at the rate of one per second.

How long does it take me?

Answer 19

a few thousand years

Question 20

Kepler’s first law

Answer 20

The orbit around the sun is elliptical, (with the sun at 1 focus)

Question 22

Kepler’s third law

Answer 22

Distant planets orbit at slower ave speeds following the ratio

Question 24

Mass

Answer 24

Amount of stuff in a body

Question 25

Kepler’s second law

Answer 25

As a planet orbits the sun, it sweeps out equal areas in equal time (faster nearer to sun)

Question 26

Momentum

Answer 26

The quantity of motion of a moving body = mass x velocity

Question 27

How to find Acceleration from gravity

Answer 27

Sub F = M x A into the universal law of gravity, note it will not depend on the mass of the accelerating object

Question 28

Universal law of gravity

Answer 28

Question 29

Earth gravity

Answer 29

9.8m/s2

Question 30

Why can’t we see a galaxy 15 billion light-years away?

Answer 30

Because the universe didn’t exist 15 billions years ago and so we cannot see 15 billion light-years away

Question 32

Newton’s second law

Answer 32

Acceleration of an object is dependent upon two variables (Force = mass x acceleration)

Question 33

Are the forces and accelertion between 2 interacting objects always equal

Answer 33

Forces will be equal, accelerations are not

Question 34

Newton’s third law

Answer 34

For every force there is always an equal and opposite reaction

Question 35

Conservation of momentum

Answer 35

Total momentum of objects cannot change unless external forces act on them. Interacting objects exchange momentum through equal and opposite forces.