Relativity

Question 1

Can you write what the Lorentz factor is?

Answer 1

𝛾 = 1 / (sqaure root) 1- v^2/c^2

Question 2

What is a reference frame?

Answer 2

The POINT OF VIEW of an observer who is STATIONARY.

Question 3

What are INERTIAL reference frames?

Answer 3

Inertial reference frames are when BOTH objects are either moving at a CONSTANT speed, or they are STATIONARY.

Question 4

If 2 observers are in INERTIAL reference frames to each other, who is correct??? who is wrong???

Answer 4

BOTH observers will be CORRECT from their OWN point of view = > because the laws of physics will act normal in each of their reference frames, sooo even though they see DIFFERENT things, both are still correct!

Question 5

a) Imagine a car moving at a speed of 200m/s. Kaeya who is in the car throws a ball forward at a speed of 60m/s…what is the speed of the ball?

Answer 5

a) The ball would move at the 60m/s when it was thrown PLUS the original speed of the car.
60+200= 260m/s

Question 6

Noww,

b) Imagine the lights of the car turn on as it is still moving at 20m/s. What is the speed of light..?? 0-0

Answer 6

b) The speed of Light is ALWAYS CONSTANT at 3x10^8

Question 7

The Theory of Relativity has 2 postulates to it….so,

What is Einstein’s 1st Postulate?

Answer 7

“In ALL INERTIAL FRAMES, the Laws of Physics have the same form.”

What does this mean?
If 2 observers have are in inertial reference frames, everything will act as NORMAL.

Question 8

What is Einstein’s 2nd Postulate?

Answer 8

“The speed of light is constant (c).”

Question 9

Draw a triangle. Label the top point 1, the left point 2, and the right

Imagine Yvette is super fast and running along the horizontal line. Su is at point 2 and Jade is at point 3 holding flashlights that are pointed towards 1.

When Yvette runs along the line and PASSES point 1, Su and Jade IMMEDIATELY turn on their lights.

Q1: From the reference frame of Yvette, whose light reaches her first??

Answer 9

Q1: Both lights from Su and Jade reach her at the SAME TIME

Question 10

Q2: Su doesn’t believe Yvette lol and thinks that Jade’s light reached her first. Why?

Answer 10

Q2: From Su’s POV, Yvette is moving towards Jade’s light so it looks like she reached it first.

Question 11

Note to remember about Simultaneity
(flip me over! :D)

Answer 11

(for inertial reference frames)
2 things happening at the same time for one observer, may look different to an outside observer.

Question 12

…I forgot…help me remember what is Time Dilation??

Answer 12

Time is not an absolute value! It can speed up/slow down depending on the reference frame (perspective).

Question 13

If something is moving FASTER relative to you, what happens to their time? 0-0

Answer 13

Their time would seem to SLOW DOWN.

Question 14

What is proper time?

Answer 14

The time measured from the observer who is stationary relative to the other.

Question 15

What is the formula to calculate time dilation?

Answer 15

t=𝛾t0

Question 16

Why is time dilation only noticeable for speeds close to c?

Answer 16

For normal speeds (like 100m/s or 60 km/h) in the lorentz factor, this part –> v^2/c^2 is a smaall value, so the whole thing is almost like 1/1 which means t0 is pretty much the same as t.

(feel free to ask yvette for this :”) idk how to type it well)

Question 17

You are stationary and looking at something moving really fast.

Time for this moving object seems slower right? Then what does this mean for the distance of that object? What would it look like to you?

Answer 17

It would look like the object is travelling in a zig-zag motion /\/\/ which means the distance looks GREATER to you.

Question 18

Tell me about the Twin Paradox…why doesn’t it work?

Answer 18

Because the motion of the spaceship is ACCELERATING!!! We only look at CONSTANT speeds 0-0

so it’s not a paradox because we don’t know about that crazy stuff yet :”)

Question 19

What is Length Contraction?

Answer 19

A MOVING object relative to a stationary observer appears SHORTER in the direction of travel

Question 20

What is the formula for length contraction??

Answer 20

pretty much the same as time dilation :D

l = l0 x (square root)1 - v^2/c^2
OR can be written as
l = l0/𝛾

Question 21

If a car is travelling up, what happens to the dimensions if the length is contracted?

Answer 21

The car would look flat because it contracts upwards.

Question 22

What happens to the momentum of a person who is MOVING relative to you?

Answer 22

THEIR momentum would be GREATER than yours because their speed is close to the speed of light.

This also means that their mass is increasing as well (but that’s explained in another card :))

Question 23

Whats the formula for momentum?
& Whats the formula for RELATIVISTIC momentum?

Answer 23

Normal: p=mv
&
Relativity: p=mv𝛾

Question 24

If a 1kg apple is on a spaceship relative to an observer on earth, what happens to the apple’s mass from the reference frame of the observer?

Answer 24

The mass of apple INCREASES because it’s MOVING relative to the observer.

Question 25

Whats the formula for relativistic mass?

Answer 25

i’m sure you notice the pattern by now.. 0-0

m=m0𝛾

Question 26

Why can’t objects have speed FASTER THAN THE SPEED OF LIGHT?????????? :O

Answer 26

Because in the r.momentum formula, v^2 = c^2, which means the DENOMINATOR OF lorentz factor would be EQUAL TO ZERO –> UNDEFINED therefore NOT POSSIBLE