Let's now give Mr. Flat Hat a method of measuring time : a light clock
consisting of two parallel mirrors with a light beam bouncing between them, perpendicular
to the direction of motion. The mirrors are a distance d apart, so Mr. Flat Hat sees the
round-trip time as
,
where c is the speed of light and d is the distance between the mirrors.
The light beam bouncing backwards and forwards measures out equal units of time, just as the ticking pendulum of a grandfather clock does.
The picture shows the difference between what Mr. Flat Hat and Mr. Round Hat see. (NB : They observe the same value for c, and the same value for d.)
Activity 1 |
Use Worksheet 1 to work out by how much Mr. Round Hat sees the round-trip time extended.
The Gamma Factor |
The factor that says how much the sparrow sees the round-trip time extended by (the
time dilation factor) is given the symbol 
(gamma), and is often referred to as the 'gamma factor'.
is always greater than 1, but is very close to 1 at
low ('every-day') velocities, where there is no appreciable time dilation.
In Activity 1, you should have found that:
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