In what direction will the bike move?

valamhic

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An interesting thing I found when doing it with my bike balanced as best as I could without interference, as per the question, was that the pedal rotated up/towards me as the bike moved back. I thought the Matrix had broken!
Exactly. Now mark the ground (place a pen right under the pedal to mark the location) The pedal will move back in relation to the mark but not
as much as the rest of the bike. That question appeared in an Irish book/magazine I found in the dentists waiting room. I answered by post just giving the direction. A group of students in a Dublin university also got the direction right. Two right answers only.

The college decided as there was only one prize that each would have to explain. I won. If it had to be money I would have let the students have it for being such good sports, it was a pair of binocular, a good pair which are still lying around somewhere. 15 years ago.
 

valamhic

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I meant more that I'd try to do the test/question while on the bike, but it'll be tricky to have the force going purely backwards. I'm curious if weight/downward pressure is relevant.
If there are no stabilizers, get someone to hold it up but not to prevent it moving. Just get them to hold the tip of the handle bar with an outstretched arm as loose as possible.
 

Ire-land

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If there are no stabilizers, get someone to hold it up but not to prevent it moving. Just get them to hold the tip of the handle bar with an outstretched arm as loose as possible.
I managed both jobs well enough, well enough to find out the right answer... eventually. Cool question, fair play.
 

Ted

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Every part moves backwards. Generally to all replies, I could not include every possible eventually in the question because it would be endless.
I covered a few important points and said the bike was a standard one in every way. I had to say the handle bars were locked because if the front wheel could turn (steer) the bike would not be straight and readers might think that was the trick of it. It is not locked to a pole, just locked to prevent it turning. The size of the cog wheel are normal to a big one on the pedals and a small one on the wheel.
Wrong answer.
As with all wheels, the part touching the road does not move. If it does move we call it a skid.
 

Ire-land

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Wrong answer.
As with all wheels, the part touching the road does not move. If it does move we call it a skid.
But, like the pedal, wouldn't the contact point of the tyre move backwards relative to where it started, though rotating up?
 

valamhic

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I meant more that I'd try to do the test/question while on the bike, but it'll be tricky to have the force going purely backwards. I'm curious if weight/downward pressure is relevant.
If you are in the bike you are an engine. The bike will go forward if you turn the pedal. If you push the pedal down while your other foot is on the ground, the bike will go forward because the pressure is neutral direction
 

valamhic

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Wrong answer.
As with all wheels, the part touching the road does not move. If it does move we call it a skid.
There js no skid, you can assume there is not a skid, that would make the question a trick.. A waste of readers time, I would not do that. The Tyre does not slip or skid, it contacts the road in the normal way. The centre of a wheel on a bike moves at the same speed as the bike itself. The top
moves at twice the speed of the bike in a forward direction while the bottom is stationary on the horizontal but only at the exact point of contact as the bike moves the rim lifts up from the surface gaining angle to it until it is half way up, If the bike is moving, there is no point at which the bike frame is stationary or any part of the rim is stationary. The rim is in angular motion. Its motion is in a different frame of reference to the frame
 
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Storybud2

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it is a free wheel cog on the back, the "pressure" applied by the man just pushed the mass of the bike backwards, it does not and cannot propel the bike via the cogs,, what the fook am I missing here ?
 

Ted

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There js no skid, you can assume there is not a skid, that would make the question a trick.. A waste of readers time, I would not do that. The Tyre does not slip or skid, it contacts the road in the normal way. The centre of a wheel on a bike moves at the same speed as the bike itself. The top
moves at twice the speed of the bike in a forward direction while the bottom is stationary on the horizontal but only at the exact point of contact as the bike moves the rim lifts up from the surface gaining angle to it until it is half way up, If the bike is moving, there is no point at which the bike frame is stationary or any part of the rim is stationary. The rim is in angular motion. Its motion is in a different frame of reference to the frame
That's wot I just said.
 

valamhic

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it is a free wheel cog on the back, the "pressure" applied by the man just pushed the mass of the bike backwards, it does not and cannot propel the bike via the cogs,, what the fook am I missing here ?
If the two cog wheels were exactly the same diameter, the effect of pushing the wheel would be the same as if the pedal were attached to the wheel itself. If the pedals swings in a circle of 8 inches and the wheels have a diameter of 16 inches,, its the same as if the pedal was attached directly to the wheel 8 inches from the centre. An inch push back on that pedal would move the bike frame back 2 inches.
 
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valamhic

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That's wot I just said.
A mark on the wheel rim will show that that mark moves towards and away from a point farther away from the centre than the rim itself. The same as a piston attached to a connecting rod driving a crank. There has to be a point where it reverses direction. However there is only one time frame moment when it is at top dead centre. Only one. As time does not stop in nature, the point does not stop. Speed is distance over time.
 
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