Lecture 17

Question 1

What are the key ideas of special relativity?

Answer 1

• the speed of light is constant for everyone
• the laws of nature are the same for everyone

Question 2

What is special relativity used to compare?

Answer 2

The motion of one object relative to another when they are both moving at constant velocity

Question 3

What is a frame of reference and what are the two types?

Answer 3

A reference frame is a fictitious world that moves with that person (the observer)
1. inertial: moving at a constant velocity
2. accelerated: accelerating or in a gravitational field

Question 4

Why can’t we reach the speed of light (according to what you see)?

Answer 4

All observers must see light travelling at c, hence you must be moving more slowly and cannot reach the speed of light

Question 5

What are the consequences of approaching the speed of light?

Answer 5

• fast clocks tick more slowly
• simultaneity is relative
• the shape of fast objects change
• the mass of fast objects increases

Question 6

*What is the time dilation formula?

Answer 6

t’= t /γ

Question 7

*What is the Lorentz factor formula?

Answer 7

γ= 1/sqrt(1-(v^2/c^2))

Question 8

*What is the length contraction formula?

Answer 8

l’= lγ

Question 9

*What is the mass increase formula?

Answer 9

m’= mγ

Question 10

What are the three effects seen as you approach the speed of light?

Answer 10

1. Aberration: distortion of shapes
2. Doppler effect: wavelengths are blueshifted moving towards the source
3. Enhanced intensity of the source