Jan 7 th Summative will be on Jan 19 th and 20 th Our final is on Jan 29 th in the Caf at 9:30. Our colour is yellow. Posters due Jan 15th More Special Relativity

Time Dilation Another thought experiment! Imagine a fast moving train. You are on the train, and you shine a flashlight from the floor to the ceiling. You measure the time it takes for the light to travel that distance, and call it Δt s (s for stationary, because the flashlight is stationary with respect to you). The distance to the light travels is therefore cΔt s (diagram) An observer on the ground also measures the time it takes for the light to travel from the floor to the ceiling. He calls it Δt m (m for moving because the flashlight is moving with respect to him). The distance the light travels is therefore cΔt m (diagram)

An astronaut traveling at 0.90c, relative to Earth, sleeps for 8 hours. According to observers back on Earth, how long has he slept?

The effect is sometimes expressed as “Moving clocks run slower”. If you send a clock up in a fast spaceship, when it comes back to Earth, it will be slightly behind as compared to clocks that stayed on the ground. This effect is real and has been experimentally confirmed. Technology that involves fast moving satellites with accurate clocks (like GPS) must take this into account.

Homework: Page 568 # 1, 2 Page 573 # 1, 2, 3, 4