Special Relativity


This topic introduces you to the concept of special relativity. It covers the key themes, with some worked examples. After each theme you will be asked to work through some questions on the Relativity Worksheet document. In your studies you will probably have covered Einstein’s special relativity to a small extent. This resource will focus mainly on problem solving in special relativity.

The Two Postulates of Special Relativity

These are the starting points for all of special relativity and you should make sure you understand and remember them:

● The Principle of Relativity: the laws of physics are the same in all inertial (non-accelerating) frames. There are no privileged observers.

● The Principle of Invariant Light Speed: observers in all inertial frames agree upon the speed of light. In other words, no matter how fast you’re going, you always see light to travel at the same speed, c. The speed of light is ALWAYS the same.

The second postulate may appear to be obtainable from the first, since Maxwell showed that the speed of light is determined by fundamental physical constants, which by the principle of relativity are the same in all frames.

However, the important point is that the second postulate means that no matter how quickly you are travelling, you always see light travelling at the same speed, whether it is moving in the same direction as you or the opposite direction.

There are many consequences of adopting these postulates, but the two most important ones are that time is relative and nothing can go faster than the speed of light. Newtonian physics assumes that all observers agree on the times at which events occur. Einstein blew this out of the water, as we shall see.

Video Resource

Video Resource

Resource activities

Time Dilation

In relativity different observers can (correctly) disagree on
the time between events.


Length Contraction

We have seen that time intervals between events appear to be different lengths depending upon the relative speeds of observers in different inertial frames. Special relativity gets even stranger still. If someone is moving relative to us they actually look thinner in the direction of travel!


The Lorentz Transformation

Lorentz transformations are the relativistic equivalent of the classical Galilean transformation, where, due to time dilation and length contraction, there are added complicating effects.


Worked Examples

Here are the worked examples collated.


Reflective questions

To answer and record these questions you will need to have an account and be logged in.

Task 1

What are the key arguments, concepts, points contained within it?

Task 2

What are you struggling to understand?

What could you do to improve your understanding of these concepts/terminology etc.?

Task 3

What further questions has this resource raised for you?

What else are you keen to discover about this topic and how could you go about learning more?

Can you make any links between this topic and your prior knowledge or school studies?

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Further reading