In what direction will the bike move?

Superhans

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You said it had a lock on it to prevent it from being stolen.

Thus if the bike is locked, it should not move at all as the lock will prevent it from moving.

Anything other than similar below would suggest the bike could be stolen even though you cannot turn the handlebars.


 

Notachipanoaktree

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There is a perfectly flat tarmac surface on a street and it is a calm sunny warm day. Jack has just got his first bicycle and is learning to ride it. It is a large child's bike
with stabilizers on the back wheels to keep it upright. The front wheel is aligned with the back both facing in he same direction and Jack puts a lock on the handle bars
which prevents it turning and being stolen. The 2 wheels are free to revolve freely. It has just one gear, a big cog wheel on the pedals and a small free wheel on the back wheel connected by a normal chain. which allows Jack to coast forward down hill without the pedals going round. Its a plain standard traditional bike in every way.

The right pedal is down near the bottom at 5 o'clock and a man standing there talking to his neighbour has no evil intent. This man puts his foot against the right pedal and pushes it backwards. The pressure is enough to move the bike itself, The man is not in contact with the bike at all.

Question: Does the bike move forward or backwards?
Dopey Irish teacher. For sure.
 

Ted

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OK, thanks for all the genuine replies.

It will go backwards. It will move opposite to the force being applied.
And post #6?
It's a genuine question.
 
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I do not want to waste time but my understanding is that if the pedal wheel is actually smaller than the flywheel at the rear, then the bike will move forward.
Also.
When pulling on a thread on a spool. Pulling straight back will see the spool coming back. But pulling back and up, will see the spool going forward.
 

Ire-land

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I was just about to ask the above question in relation to front and rear cog size, and also if the weight of the bike matters. I wasn't out today to try, but if you're on the bike and you make the same effort from 5 o'clock, would you then move forward? I have the sense that if there's more downward pressure than backward pressure, then the gearing would activate to move it forward?

Having said that, I also had the sense that the bike would move forward to begin with! Facepalm
 
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I was just about to ask the above question in relation to front and rear cog size, and also if the weight of the bike matters. I wasn't out today to try, but if you're on the bike and you make the same effort from 5 o'clock, would you then move forward? I have the sense that if there's more downward pressure than backward pressure, then the gearing would activate to move it forward?

Having said that, I also had the sense that the bike would move forward to begin with! Facepalm
You will not find a bike with a bigger flywheel. The man had to have one built to demonstrate what would happen. It is on utube
 

Ire-land

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You will not find a bike with a bigger flywheel. The man had to have one built to demonstrate what would happen. It is on utube
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.
 

valamhic

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And..
When the bike moves, what part of it doesn't move?
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.
 

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.
An independent force is applied backwards on the pedal which is not connected to the bike at all. It is in the backward direction.
 

Ire-land

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An independent force is applied backwards on the pedal which is not connected to the bike at all. It is in the backward direction.
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!
 

valamhic

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The question tends to be counter intuitive. You think, "if the pedal is moved in a clockwise direction, it will revolve the rear wheel through the chain in a clockwise direction" It would if the rider on a bike did it. However it is a fundamental law of physics that when a force is applied in one direction it will move the object in that direction. Yes the pedal will move backwards at a slower speed than the rest of the bike but the entire bike will move backward. Nothing on the bike will move forward.

Think of it as if there is a shaky post in the ground 5 feet high with 9 inches stuck in the ground. Soft ground. You place your tow against it and press it towards the north. All of the post will move backwards bit the top will move a lot more than the bottom.
 
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