Hi all would just like to mention that the following blogs on special relativity are from my notes taken at uni. I have tried putting the ideas that were taught to me by my professor into my own words but really all the work is his and i've just stolen it ha ha har. I will not name my professor but all credit should go to him and thanks for letting me post this online. Hopefully it will help me in understanding the subject spark a few discussions and some people might find it an interesting read.

Lecture 1 Special Relativity

First we must define relativity in the classical sense:

Relativity is events that happen with respect to a certain view point (reference frame). So are a set of coordinates in the x,y,z direction with an observer located at the origin. An internal reference frame is one that is not accelerating. This does not mean there is no motion just that the motion is at a constant rate. This then implies that any internal reference frame must travel at a constant velocity with respect to any other internal reference frame.

"There is no unique internal reference frame and no absolute velocity can be measured."

Example

A train goes by and someone throws a ball from one end to the other.

A person on the train would see it travel, from their internal reference frame at say 12 meters a second. A person on a bank watching the train go by would see from their inertial reference frame the ball travel at 12 meters a second plus the speed of the train. Who is correct? Well both are which means there is no unique reference frame and no absolute velocity.

Galilean Transformations

Coordinates in one frame are related to coordinates in another frame.

Newton’s 1^st and 2^nd laws are true in all inertial reference frames.

Newton’s 1^st law

If no external force acts then an object in motion stays in motion of if at rest will remain at rest

Newton’s 2^nd law

If an external force acts on an object then it will accelerate directionally proportional to the force, the constant of proportionality being mass.

In an inertial reference frame (A) a car is moving at constant velocity (U) now let another inertial reference frame ( B ) move along the horizontal x axis at a velocity (V) then the velocity of the car in this new frame is simply the velocity of the new frame (V) minus the velocity (U) of the car.

Position transforms

If you have in inertial reference frame (A) a particle moving along the x axis then an internal reference frame ( B ) moving along the x axis with a difference of velocity (U) multiplied by time (T), then the position of the particle in inertial reference ( B ) will be related to that in internal reference (A) by.

Position of (A) = Position of ( B ) + (U) x (T)

Note: acceleration does not change between reference frames.

Hope this is straight forward to understand any questions more than happy to talk about