Stagecoaching!

[Pete]

If you have a bicycle read on!
If you do not have a bicycle this might not be very interesting.

:confused: Have you ever been riding your bike at night under streetlights?
:idea: If you have ever watched Western movies the wheels on the coach go backwards all the time they are going forward.
:idea: Get on your bike at night under streetlights and ride at various speeds until the tread on your tyres goes backwards just like those stagecoaches. Even better get to a speed where the tread appears to stay still.
:eek: Bizarre but it works. Can someone explain why?
:D I discovered this coming back from the pub. It works riding to the pub also; so I can't blame this on the beer.
(NSSwimmer! this will appeal to your humour)

Please post results of your investigations here!:)

[nsswimmer]

hehehe ^^

[Unfit]

the reason it does this is because the light from the lampost is actually intermittant, not constant, so you get an effect like a strobe light where for very short periods of time you can't see anything. (ever been to a nightclub where stobe effects are being used and you get the idea) so you think the wheel is going backwards because the speed of the wheel compared to the speed of the stobe makes it look like that.

[sub24]

If you take a pencil and wave it in front of your computer monitor you can also see a strobe effect. Some people can get sick because of this effect, which also occurs with a TV screen, and flourescent lights. Some schools are trying to move away from that type of lighting system to an indirect lighting system to enhance learning. Indirect lighting means the light is reflected off of something like the ceiling to light up the room.

A great way to swim is with all the lights off except for the lights in the pool. A beautiful effect, and shows how indirect lighting is much more pleasant than 'normal' lighting. A good way to watch swim technique too.

[Pete]

;)
Thank you physicists. So what variants can be used to establish how fast I need to cycle to keep the stagecoaching constant?
Can it be distance between lamp-posts?
Height of lamp-posts?
Luminocity of the lamps?
Size of bike wheel?
Or all of the following?;) I feel a dissertation coming on.
:devil:
:confused: Where have you been to try out Stagecoaching?

[Steve]

One other thing - with regard to old films, the reason the wheels appear to be going backwards is related to the shutter speed of the camera, rather like the strobing effect of the lights as noted before, but this only really works with spoked wheels.

The spokes are evenly spaced around the wheel perimeter. Each time the shutter clicks a snapshot of the wheel is taken, with the spokes in a given position. For the wheel to appear to be moving backwards the speed of revolution of the wheel has to be such that in the gap between shutter clicks the spokes do not have time to move the full distance between them. I.e. if two adjacent snapshots were superimposed the spokes would appear to have moved slightly backwards. If they don't move very far though, the wheels appear to be moving forward - it's all to do with how your brain interprets the image. If they move exactly the distance between spokes in the time between shutter clicks, the wheel would appear to be stationary.

So in terms of Pete's bike tyres, I think the speed of cycling required to keep the 'stagecoaching' constant is dependent on the distance between treads and the frequency of the strobing of the streetlights. Since the speed of light is significantly faster than Pete's cycling (I hope ;) ) I reckon that the height of lamp posts etc should have very little effect on this.

You can sometimes see this effect with the naked eye on spoked car wheels, as there is a limit on how fast the brain can interpret changes in the images presented by the eyes (this is how television produces apparently moving images from 25 pictures per second) producing an effective shutter.

[Pete]

:rolleyes: :rolleyes:
Went out with my Imperial measure, very collectable, micrometer; measured and converted the tread measurements. About 11mm with 9mm gaps. Not sure of the standard diameter of mountain bike wheels. Streetlamps are about 25m (short course) apart and my speed was just under 9 mph.:devil:
Do they still use strobe lights on record decks so that they can syncronise beats when mixing tracks together?
But to get back to the fun thing! Can you "stagecoach" keeping the tread still for more than a minute?:angel: :confused:

[nsswimmer]

wut about propellers??? like when you watch PEARL HARBOR (josh hartnett!!! *swoon* keke ^^ newayz...), the plane propellers start whirling and you can watch it, but then when it goes faster, the propeller blurs and u can see it look like it's almost goin backwards. is that kinda the same???

[Steve]

Because I'm a bit of an anorak :eek:, I decided to work this out, using a combination of A-level maths and Physics and my first year university mechanics.

I reckon that the "stagecoaching" effect should occur with Pete's tyres appearing stationary at whole number multiples of 4.47mph (i.e 4.47mph, 8.94mph as Pete observed, 13.41mph, 17.88mph and so on). This assumes the bike has standard 26" mountain bike wheels. The effect of wheels moving backwards or forwards occurs either side of these speeds.

So there you go :D If anyone's really interested I can send you the calculation...you're not interetsed?...I'm not surprised ;)

[Pete]

Cheers Steve! Will try the other speeds out at some point.
Anyone else given it a try yet?

[stella]

Pete. I hope you are keeping an eye on the road for scarey cars and the like. You know you should always be vigilant on the road. There are some mad folk about just ready to knock anyone found staring at their tyre tread instead of the traffic just for fun you know! I think we should point this out to all the impressionable people viewing this site in case this encourages a spate of cycling accidents. ;) :devil:

Remember kids - Pete is a trained professional!

No but seriously, a very thought provoking discussion but how have you lot got the time????? :rolleyes:

[Pete]

:p Stella! I keep my stabilisers on:cool: And ride on the pavement:devil: Not! You don't have to look down; perpheral vision allows you to view the wheel all the time.
So does this mean someone is going to pay me to be a professional "Stagecoacher"?:idea: :idea: :idea

[stella]

;)

[BigFish]

Originally posted by Pete
Went out with my Imperial measure, very collectable, micrometer; measured and converted the tread measurements. About 11mm with 9mm gaps. Not sure of the standard diameter of mountain bike wheels.

This I find ridiculuous (not the rest of it mind)!

You went to the trouble of using a micrometer to measure the tread measurements to such accuracy, yet you couldn't be bothered to measure the diameter of the wheel?

Or were you just showing off about the micrometer bit? :confused:

[Pete]

:devil: I have a micrometer but not a tape measure believe it or not and when you have something that measures precisely you use it and when you don't have the knowledge you pass it on. If I wanted to show off my micrometer I would chase the "Antiques Roadshow". Come on Dave. Off Topic is light hearted.
I really like the way all the scientific stuff has come out of a fun posting.

"Stagecoaching" is here to stay. You read it here first!:angel:

[BigFish]

Originally posted by Pete
If I wanted to show off my micrometer I would chase the "Antiques Roadshow". Come on Dave. Off Topic is light hearted.
Ooops sorry Pete, I thought I was being light hearted.

[Unfit]

steve, i'm afraid you're lowering the status of us civil engineers in society by showing what an annorak you are.

however, from one anorak to another, very impressed you went to all the trouble of actually doing the calculation! very devoted to the cause!!