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Imagine the ball travels at 1m/s.
If the thrower is travelling away from you at 1m/sThe ball will never hit you...
Imagine the ball travels at 1m/s.
If the thrower is travelling away from you at 1m/s
The ball will never hit you...
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NotThamesWater
NickCJ
Greenbank
Just like Doppler with a siren.
Coming towards you: higher pitch = higher frequency = blue
Going away: lower pitch = lower frequency = red
Why is something coming towards you higher energy? Imagine someone is 10m away from you, and throws a ball at you every second for 10s. Imagine the ball travels at 1m/s.
If the thrower stands still, you get hit with 10 balls in 10 seconds, after an initial 10 second wait. This is the "true" frequency as seen by the thrower.
If the thrower is travelling away from you at 1m/s, the first (or zeroth) ball takes 10s to get to you, the second takes 11s (as the thrower is now 1m further away), the third takes 12s etc. until the 10th ball, which takes 20s. But the 10th ball also leaves 10s after the 1st, so you've see 10 balls in 20s total. The frequency is halved.
If the thrower is coming towards you at 1m/s, the balls are travelling at the same speed as the thrower, so you are going to be hit by 10 balls all at the same time (high frequency) after a 10 second wait - like a sonic boom.
Now instead of balls substitute power or wavelengths or whatever