🪐W4 L2 - Explaining patterns - Mass, gravity, and tides Flashcards
Learn about mass, spacetime, gravity, orbits, and tides.
In a sentence, state Newton’s First law of Motion
An object at rest remains at rest, an object in motion at constant speed remains in motion unless acted on by an unbalanced force.
State Newton’s Second Law of Motion
The acceleration of an object depends on the mass of the object and the amount of force applied.
What mathematical relationship did Newton find gravity follows?
The inverse square law
What is the inverse square law for gravity?
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.)
Is the gravitational constant small or large?
Small
State the numerical size of the gravitational constant
6.67 x 10⁻¹¹ m³ kg⁻¹ s⁻²
State the formula for Newton’s Law of Universal Gravitation
Fg = G (m₁.m₂) / r²
What is the common point around which two objects orbit?
The barycentre
Can the barycentre be within an object?
Yes, if it has very high mass compared with its partner(s)
Is the barycentre for the Sun inside it?
No, it is just outside it
Why is the barycentre for the solar system not inside the Sun?
Because of Jupiter
Where is the barycentre for the Earth moon pair?
Just inside the Earth’s crust
What does mass do to spacetime?
Bends it
How does time run on Earth compared to being in space?
Slightly slower
What speed does gravity travel at?
The speed of light
Name the two types of orbits
Bound (elliptical) and unbound
What are the two types of unbound elliptical orbits?
Unbound parabolic and unbound hyperbolic
What do unbound orbits require?
Sufficient escape velocity
Name 3 things that can make an object gain or lose orbital energy
1) friction or atmospheric drag, 2) gravitational encounter, 3) thrust
What velocity does a rocket need to achieve escape velocity from Earth?
11.2km/s
What causes the tidal bulge on the opposite side of the Earth to the moon
It’s where the moon’s gravitational pull is weakest so water sits there
When the sun and moon are aligned along the same axis what kind of tide do we get?
Spring tide
Is the tidal bulge ahead or behind the moon’s position?
Ahead
Why is the tidal bulge ahead of the moon
The water is dragged along by the Earth
How much does the moon move solid objects to cause solid tides?
20-30cm
What is tidal drag doing to Earth’s rotation?
Slowing it down making the days longer
What is tidal drag doing to the moon’s orbit?
Accelerating it in its orbit and moving it further away from the Earth (at about the same rate your fingernails grow!)
What devices on the moon do we use to check the moon’s distance?
Retroreflectors on the moon - we bounce lasers off them
In Earth radii, how far away is the moon?
60 Earth radii
What is the Roche limit?
The distance where the gravity of a large body is strong enough to prevent any smaller body from being held together by gravity.
