Lecture 11

Question 1

Escape speed formula

Answer 1

11.2√(mass of the body/ radius of the body)

Question 2

If you keep mass the same but reduce the radius what happens?

Answer 2

The escape velocity will increase

Question 3

Reducing the radius by a factor of 4 does what to the escape speed?

Answer 3

doubles the escape speed (the denser an object the higher its escape velocity)

Question 4

Event horizon

Answer 4

the surface of a black hole; the point from which nothing can escape from it (surface of an imaginary sphere having a radius equal to the Schwarzschild radius and centered on a collapsing star)

Question 5

Schwarzschild radius

Answer 5

the radius to which an object would have to be compressed to form a black hole (3km times the mass of an object)

Question 6

Stellar mass black holes

Answer 6

stars with original masses greater than 24 times the mass of the sun;”baby” black holes, millions in the galaxy

Question 7

Supermassive black holes

Answer 7

millions or billions times the mass of the sun; one at the center of every galaxy

Question 8

How do we know black holes exist?

Answer 8

The effect it has on stars and other materials

1. stars (in a binary system) passing black holes will be ripped apart by its gravitational pull and emit powerful x-ray radiation
2. large clusters of stars at the center of many galaxies move rapidly, the motion (rapid movement) is believed to be caused by a massive invisible object close by

Question 9

Steps of a black hole devouring a star

Answer 9

1. sun-like stars on an eccentric orbit plunge toward the supermassive black hole
2. strong tidal forces near the black hole distort the star, if the star passes too close it’s ripped apart
3. part of the star facing the black hole streams towards it and forms an accretion disk; the remainder of the star expands into space
4. near the black hole magnetic fields power a narrow jet of particles moving near the speed of light

Question 10

Special relativity experiment

Answer 10

done by michelson and morely in 1887 to find the aether of space in which light supposedly moved, used the rotation of the earth on its axis and around the sun to measure the speed of light

Question 11

Special relativity experiment findings

Answer 11

the experiment failed; found that the speed of light in a vacuum does not change, regardless of the speed source or the observer

Question 12

(Special theory of relativity)

The speed of light in a vaccum

Answer 12

is the same to all observers, it is the maximum speed in the universe

Question 13

(special theory of relativity)

Only ___ velocities between observers matter

Answer 13

relative

Question 14

___ nor ___ can be considered independently

Answer 14

Space; time (they are one entity called spacetime)

Question 15

time is not fixed

Answer 15

it can speed up or slow down depending on the reference frame (relative motion of the objects)

Question 16

What are the two strange conclusions drawn from special relativity

Answer 16

Time dilation and length contraction

Question 17

Time dilation

Answer 17

the closer you are to a massive object the slower time passes

Question 18

Length contraction

Answer 18

occurs when either the observer or object is in motion and occurs only in the direction parallel to the direction of motion

Question 19

Length contraction is also known as

Answer 19

Lorentz contraction

Question 20

General relativity

Answer 20

there is no way to distinguish gravity from an accelerating frame of reference (equivalence principal)

Question 21

Because of Einstein’s equivalence principle, lead him to believe spacetime is?

Answer 21

curved

Question 22

There is no such thing as ____. objects move as they do because they follow what?

Answer 22

“gravitational force”; they follow the curvature of spacetime

Question 23

what causes gravitational waves?

Answer 23

if 2 massive objects accelerate towards each other they will distort (or accelerate) the fabric of spacetime