Level 7: Special relativity

Space and time · level 7 of 8 · rough age 15-16 (a guide for parents; anyone can start anywhere)

Light travels at the same speed for everyone, however fast they move. That one fact, which Einstein took seriously in 1905, means moving clocks run slow and moving lengths shrink. This level builds the rules from a clock made of light, checks them with muons from the sky, and ends with the clocks on a trip to Mars.

Lesson	You will be able to
Light speed is the same for all	State Einstein's two starting ideas and the evidence behind them
Time dilation	Use the Lorentz factor to find how much a moving clock slows
Muons	Explain why muons from the upper air reach the ground
Length contraction	Find how much a moving length shrinks
Nothing goes faster than light	Explain the speed limit using energy and adding speeds
Clocks on a trip to Mars	Estimate small time differences for slow speeds

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