Special relativity in strips

This task is based on the activity created by Trevor Register and can be found here

Make sure you have watched the Minute Physics on the previous page. Create a set of strips out of paper and model relative motion as we understand it in classical physics.

The width of the stripe represents a unit of time passing, so when we rearrange to the Cat's point of view the relative velocity changes but he distances and times remain the same.

For the rest of this activity, use a slide on a side show. create a similar scenarios the one below.

In the image below.... from the Cat's frame of reference the police car moves away at a constant speed and the light from its siren moves away at a much fast but also constant speed.

The straight lines represent the constant speeds. By Einsteins first postulate the speed pf light is a constant for all so this means in this experiment the gradient of this line cannot change in magnitude.

Hints in recreating this.

Make one strip first with your three objects and then make the copies. Draw in the lines and then move the objects to represent their movement and constant speed. Write a comment on this first slide explaining what it represents.

Once you have created these strips, group the objects on each strip so their position can't change and then make a copy of the slide.

Now rearrange the strips so that we observing from the police cars frame of reference.

Hint: Draw a horizontal line first from the police car, then line each up at the same spot.

Write a comment on why this illustrates the breaking of Einstein's second postulate.

To solve this problem we must assume that time is not fixed across each frame of reference. So now try to line up the photons along the speed of light line.

Take another copy of your first slide and add the horizontal line. This time attempt to line up the police cars by changing the angle so the photons remain along the speed of light line. This will be tricky! Once your happy, drop a new time line and measure its length and compare the the length of the original time.

What we see is a slightly longer time. Thus we have modelled time dilation!