U4AOS1 Topic 1: Special Relativity

 

Special Relativity is Einstein’s most famous theory which filled in the gaps left by Newtonian (classical) physics.

It says that Time, Kinetic Energy, Length and Mass are relative quantities.

 All this means is that these quantities depend on how they are being observed.

Here is an example below:

If a truck is travelling at 70km/h and you are standing still. Then it is travelling at $70$km/h in your frame of reference (perspective).

However, if your friend was driving their car on the road toward the truck at 70km/h.

In their frame of reference, the truck is travelling at 140km/h

(70km/h + 70km/h = 140km/h)

and you would be travelling at 70km/h toward them.

(0km/h + 70km/h)  70km/h

Einstein’s Postulates:

1.       The Laws of Physics are the same for all inertial (non-accelerating) frames of reference.

- Whether it is stationary or travelling at a constant velocity, it will be non-accelerating. The examples above show the perspectives.

2.       The speed of light ($c$) is constant for all observers regardless of their motion.

	Special Relativity	Newtonian Physics
Space and Time	Flexible; length and time change between reference frames.	Fixed; all observers agree on measurements of time and length
Relative Speed	Not additive – no object will reach the speed of light ($c$)	Additive – all values are possible
Kinetic Energy	Not additive – no object will reach the speed of light ($c$)	Increases in proportion to ${ v }^{ 2 }$