Relativity

[Khandro]

Thoughts on my early morning walk along the river with my dog :

If a bicycle & rider are travelling in a northerly direction at 10mph. at any given moment, the top of the front wheel is travelling past the fork, so it must be travelling (in relation to the fork & ground) at 10mph plus. Meanwhile at the same moment, the bottom of the wheel is travelling in a southerly direction so it can't be moving at the same speed as fork, so it should be travelling at 10mph minus
Are the top & bottom of the wheel travelling in two directions and at different speeds? What's going on here?
Or should I have stayed in bed? :0)

[douglas9401]

I had a relative from the north who went South.

[davebro]

//davebro, just responding to the post at 09:15 every part of the wheel is moving at different speeds//

That's not quite true. Every part of the wheel at the same distance from the centre will have the same rotational speed (so it doesn't fall apart!).
For horizontal speed the two points on the rim horizontally opposite each other will have the same speed. The top (fastest) & bottom (stationary) points on the rim are the only 2 points with unique horizontal speed.

[Khandro]

dave //For horizontal speed the two points on the rim horizontally opposite each other will have the same speed.//

Yes true, but moving in different directions.

[davebro]

No - 1 is moving up and the other down. "Horizontally" they are both moving forwards at the same speed.

[Atheist]

Khandro; is this issue really worrying you? Does it make you feel wonky when you are on your bike?