🪐W4 L2 - Explaining patterns - Mass, gravity, and tides

Question 1

In a sentence, state Newton’s First law of Motion

Answer 1

An object at rest remains at rest, an object in motion at constant speed remains in motion unless acted on by an unbalanced force.

Question 2

State Newton’s Second Law of Motion

Answer 2

The acceleration of an object depends on the mass of the object and the amount of force applied.

Question 3

What mathematical relationship did Newton find gravity follows?

Answer 3

The inverse square law

Question 4

What is the inverse square law for gravity?

Answer 4

Gravitational attraction is inversely proportional to the square of the distance.

(If you double the distance, the attractive force will be 1/4 as strong (ie 2 squared); triple the distance and the gravitational force will be 1/9 as strong.)

Question 5

Is the gravitational constant small or large?

Answer 5

Small

Question 6

State the numerical size of the gravitational constant

Answer 6

6.67 x 10⁻¹¹ m³ kg⁻¹ s⁻²

Question 7

State the formula for Newton’s Law of Universal Gravitation

Answer 7

Fg = G (m₁.m₂) / r²

Question 8

What is the common point around which two objects orbit?

Answer 8

The barycentre

Question 9

Can the barycentre be within an object?

Answer 9

Yes, if it has very high mass compared with its partner(s)

Question 10

Is the barycentre for the Sun inside it?

Answer 10

No, it is just outside it

Question 11

Why is the barycentre for the solar system not inside the Sun?

Answer 11

Because of Jupiter

Question 12

Where is the barycentre for the Earth moon pair?

Answer 12

Just inside the Earth’s crust

Question 13

What does mass do to spacetime?

Answer 13

Bends it

Question 14

How does time run on Earth compared to being in space?

Answer 14

Slightly slower

Question 15

What speed does gravity travel at?

Answer 15

The speed of light

Question 16

Name the two types of orbits

Answer 16

Bound (elliptical) and unbound

Question 17

What are the two types of unbound elliptical orbits?

Answer 17

Unbound parabolic and unbound hyperbolic

Question 18

What do unbound orbits require?

Answer 18

Sufficient escape velocity

Question 19

Name 3 things that can make an object gain or lose orbital energy

Answer 19

1) friction or atmospheric drag, 2) gravitational encounter, 3) thrust

Question 20

What velocity does a rocket need to achieve escape velocity from Earth?

Answer 20

11.2km/s

Question 21

What causes the tidal bulge on the opposite side of the Earth to the moon

Answer 21

It’s where the moon’s gravitational pull is weakest so water sits there

Question 22

When the sun and moon are aligned along the same axis what kind of tide do we get?

Answer 22

Spring tide

Question 23

Is the tidal bulge ahead or behind the moon’s position?

Answer 23

Ahead

Question 24

Why is the tidal bulge ahead of the moon

Answer 24

The water is dragged along by the Earth

Question 25

How much does the moon move solid objects to cause solid tides?

Answer 25

20-30cm

Question 26

What is tidal drag doing to Earth’s rotation?

Answer 26

Slowing it down making the days longer

Question 27

What is tidal drag doing to the moon’s orbit?

Answer 27

Accelerating it in its orbit and moving it further away from the Earth (at about the same rate your fingernails grow!)

Question 28

What devices on the moon do we use to check the moon’s distance?

Answer 28

Retroreflectors on the moon - we bounce lasers off them

Question 29

In Earth radii, how far away is the moon?

Answer 29

60 Earth radii

Question 30

What is the Roche limit?

Answer 30

The distance where the gravity of a large body is strong enough to prevent any smaller body from being held together by gravity.