[Petrochemicals (OP)]

Very simple text book question, but this seems to have been overlooked by bike manufacturers. Its a bit like the helicopter either rotating the body of the helicopter or rotating itself against the air and providing lift.

When pedalling a bicycle the force that your legs exert to the pedals is transferred to the rear wheel by the chain. This force can do one of three things that i can think of

1. Rotate the wheel against the surface it is on, pushing the bike forward.

2. Rotate the frame upwards about the pivot of the wheel, so as the bike pulls a wheelie. This can be seen in the practice of pulling a wheelie where the handle bars are lifted slightly and the rear wheel rotated via the pedalsleading to a simultaneous forward and upward push, leading to a wheelie. The weight of the rider may cross the pivot axle of the rear wheel in such an occasion.

3. push the rider backwards off the pedals

The position that the rider sits to exert the force, the balance of the bike the gradient of the surface with respect to gravity will be the factors i can think of.

If all of the weight of the bike is forward of the pivot ie the axle of the back wheel, the bike will inevitably fail to rotate without intentional alteration  as the force generator is sufficiently forward of the pivot meaning any rotation of the frame of the bike is countered by the very thing that could cause rotation. This also means that aside from the 9.81 ms acceleration that the riders leg muscles work againt to create forward motion, there is also an acceleration the rider must work against just to keep level via pushing the frame downwards. If both wheels where at the same altitude ie on the flat and level., how would you calculate the efficiency of forward motion ?

Further more the rider must remain on the pedals via holding onto the handle bars, not only expending energy in the arm muscles, the force of the arm muscles must be countered by the leg muscles

[Halc]

This force can do one of three things that i can think of

1. Rotate the wheel against the surface it is on, pushing the bike forward.
2. Rotate the frame upwards about the pivot of the wheel, so as the bike pulls a wheelie.
3. push the rider backwards off the pedals

You forgot 4: 'burn rubber', where the friction between the wheel and the road is lower than the force applied.

If all of the weight of the bike is forward of the pivot ie the axle of the back wheel, the bike will inevitably fail to rotate without intentional alteration  as the force generator is sufficiently forward of the pivot meaning any rotation of the frame of the bike is countered by the very thing that could cause rotation.

Some fairly simple trigonometry will determine the force necessary to do the wheelie.
Take the center of gravity of the bike/person object.  Draw a line from there to where the rear wheel contacts the road, and another line straight down.  That forms an angle θ.  The max acceleration on the bike is tan(θ) * gravity acceleration.  So tan(θ)*9.8m/sec²
Any acceleration above that and you get the wheelie.

This also means that aside from the 9.81 ms acceleration that the riders leg muscles work againt to create forward motion, there is also an acceleration the rider must work against just to keep level via pushing the frame downwards.

Unless a wheelie is being done, no effort is needed to counter this since no acceleration in this direction occurs.  F=ma.  Zero a,  zero F necessary to keep it that way.  Yes, if a wheelie is being done, some energy is lost to the rise in the center of gravity and less to forward acceleration.

If both wheels where at the same altitude ie on the flat and level., how would you calculate the efficiency of forward motion ?

100% in theory, unless the wheel skids (the burn rubber option).  In practice, once it starts moving, efficiency drops off due to air friction, and the bike itself is not a frictionless thing.  Some energy is lost in the bearings and chain and such.

Further more the rider must remain on the pedals via holding onto the handle bars, not only expending energy in the arm muscles, the force of the arm muscles must be countered by the leg muscles

None of these contribute to (or detract from) net thrust.  Are we counting calories expended now by a body doing isometric activities?  That makes it a biological question, not one of standard Newtonian mechanics.  Yes, it takes energy for a human to sit on a bicycle and going nowhere.

[Petrochemicals (OP)]

This force can do one of three things that i can think of

1. Rotate the wheel against the surface it is on, pushing the bike forward.
2. Rotate the frame upwards about the pivot of the wheel, so as the bike pulls a wheelie.
3. push the rider backwards off the pedals

You forgot 4: 'burn rubber', where the friction between the wheel and the road is lower than the force applied.

Missed that

If all of the weight of the bike is forward of the pivot ie the axle of the back wheel, the bike will inevitably fail to rotate without intentional alteration  as the force generator is sufficiently forward of the pivot meaning any rotation of the frame of the bike is countered by the very thing that could cause rotation.

Some fairly simple trigonometry will determine the force necessary to do the wheelie.
Take the center of gravity of the bike/person object.  Draw a line from there to where the rear wheel contacts the road, and another line straight down.  That forms an angle θ.  The max acceleration on the bike is tan(θ) * gravity acceleration.  So tan(θ)*9.8m/sec²
Any acceleration above that and you get the wheelie.

exactly the point i am thinking about

This also means that aside from the 9.81 ms acceleration that the riders leg muscles work againt to create forward motion, there is also an acceleration the rider must work against just to keep level via pushing the frame downwards.

Unless a wheelie is being done, no effort is needed to counter this since no acceleration in this direction occurs.  F=ma.  Zero a,  zero F necessary to keep it that way.  Yes, if a wheelie is being done, some energy is lost to the rise in the center of gravity and less to forward acceleration.

no energy is defacto NEEDED, yet like your last point some is expended in countering the wheelie in my opinion. The leg not only pushes the pedal down, it also pushes the bike down counter to the wheelie. The rider is at 9.81, yet the bike is at  less as in the wheelie. The point is that the leg is exerting a force greater than standard due to the bike wishing to rise up ?

In the above video is a demonstration of what you say and i summise. On a bike the leg could never exert a greater force to rise against itself as the leg is powering against gravity in the first place, simply impossible, but if the haddlebars are lifted ie. the wheelie initiated, the same occours.

If both wheels where at the same altitude ie on the flat and level., how would you calculate the efficiency of forward motion ?

100% in theory, unless the wheel skids (the burn rubber option).  In practice, once it starts moving, efficiency drops off due to air friction, and the bike itself is not a frictionless thing.  Some energy is lost in the bearings and chain and such.

re the last point about working against the force of the rotation or wheelie ?

Further more the rider must remain on the pedals via holding onto the handle bars, not only expending energy in the arm muscles, the force of the arm muscles must be countered by the leg muscles

None of these contribute to (or detract from) net thrust.  Are we counting calories expended now by a body doing isometric activities?  That makes it a biological question, not one of standard Newtonian mechanics.  Yes, it takes energy for a human to sit on a bicycle and going nowhere.

Yep, but as in the body working agaist gravity to power itself, holding onto the handlebard means the force of the arms is countered by the legs, ie double the energy for the same forward motion as compared to working against gravity ?

[Halc]

Some fairly simple trigonometry will determine the force necessary to do the wheelie.
Take the center of gravity of the bike/person object.  Draw a line from there to where the rear wheel contacts the road, and another line straight down.  That forms an angle θ.  The max acceleration on the bike is tan(θ) * gravity acceleration.  So tan(θ)*9.8m/sec²
Any acceleration above that and you get the wheelie.

exactly the point i am thinking about
...
no energy is defacto NEEDED, yet like your last point some is expended in countering the wheelie in my opinion.

I considered the bike and rider to be a single unit, and any internal forces within that unit (leg on pedal, hands on handlebar) have zero effect on the max acceleration the whole thing can do without doing the wheelie.

The leg not only pushes the pedal down, it also pushes the bike down counter to the wheelie.

It doesn't counter the wheelie at all since any force downward is balanced by an upward force on the person.  The two cancel out.  If the force is too much on the pedals and the guy isn't strapped to his seat or the pedals, the sure, the guy is ejected vertically from the bicycle.

The rider is at 9.81

Don't know what that means.  Yes, gravity acceleration is 9.81 in this example.  It isn't different for something other than the rider.

The point is that the leg is exerting a force greater than standard due to the bike wishing to rise up ?

Doesn't matter.  That force is cancelled.  What matters is the force on the road and where the center of gravity of the whole thing is.  If the rider wants to accelerate harder without the wheelie, he leans forward to drive that center of mass forward and increase θ.

In the above video is a demonstration of what you say and i summise.

Notice that the wheelie dragster loses the race.  He had to back off the power to regain control, and that backing off kills it.  Notice also that the dragster could put its center of gravity far further forward, but they design it with the engine and driver all the way in the back.  Doing a wheelie will lose a race, but almost doing one will win it.

On a bike the leg could never exert a greater force to rise against itself as the leg is powering against gravity in the first place, simply impossible

As a bicycle rider, I disagree with this.  I frequently exert more force on the pedal than my own weight if accelerating hard.  This can be countered by pulling up on the handlebars (which has no effect on the wheelie) or by pulling up with the other leg.  I'm rarely in a gear where doing this removes functional weight from the front wheel.  The only times I really need to shift that center of gravity is when braking hard.
Pedaling hard produces torque, and that torque (forward action on the bike, backward reaction on the rider) needs to be internally balanced somewhere, but the torque of pedaling does not contribute to the wheelie except in an inertial sense.  A dragster could in theory do a wheelie on ice and/or without even being in gear, similar to the way an old 409 could be rocked to the side by revving the engine.  No, I've never seen a vehicle actually get its wheels off the ground in that manner, but it could be done.

Yep, but as in the body working agaist gravity to power itself, holding onto the handlebard means the force of the arms is countered by the legs, ie double the energy for the same forward motion as compared to working against gravity ?

The arms are doing an isometric activity, and thus perform no work.  No extra energy is needed for it.  The work can be measured as force * distance.  You can measure that where the tire meets the road (W_T) or where the leg moves the pedal (W_P) and ignoring friction and such, W_T is equal to W_P, making the process up to 100% efficient.

[Petrochemicals (OP)]

I considered the bike and rider to be a single unit, and any internal forces within that unit (leg on pedal, hands on handlebar) have zero effect on the max acceleration the whole thing can do without doing the wheelie.

It doesn't counter the wheelie at all since any force downward is balanced by an upward force on the person.  The two cancel out.  If the force is too much on the petals and the guy isn't strapped to his seat or the pedals, the sure, the guy is ejected vertically from the bicycle.

yep but the efficiency is altered, push your hands together, net zero acceleration, balanced force, lots of energy used ?

Doesn't matter.  That force is cancelled.  What matters is the force on the road and where the center of gravity of the whole thing is.  If the rider wants to accelerate harder without the wheelie, he leans forward to drive that center of mass forward and increase θ.

yep balanced force lots of energy no motion

  ]Notice that the wheelie dragster loses the race.  He had to back off the power to regain control, and that backing off kills it.  Notice also that the dragster could put its center of gravity far further forward, but they design it with the engine and driver all the way in the back.  Doing a wheelie will lose a race, but almost doing one will win it.

the weight is kept as close as possible to the right side of the drice wheel, more useful friction. Interesting point that almost doing a wheelie wins, thus the rotational force is expended positively, is a  very good point!

As a bicycle rider, I disagree with this.  I frequently exert more force on the pedal than my own weight if accelerating hard.  This can be countered by pulling up on the handlebars (which has no effect on the wheelie) or by pulling up with the other leg.  I'm rarely in a gear where doing this removes functional weight from the front wheel.  The only times I really need to shift that center of gravity is when braking hard.
Pedaling hard produces torque, and that torque (forward action on the bike, backward reaction on the rider) needs to be internally balanced somewhere, but the torque of pedaling does not contribute to the wheelie except in an inertial sense.  A dragster could in theory do a wheelie on ice and/or without even being in gear, similar to the way an old 409 could be rocked to the side by revving the engine.  No, I've never seen a vehicle actually get its wheels off the ground in that manner, but it could be done.

you can only exert the force of standing on the pedals, how fast the bike chooses to rotate its wheel is up to it, you cannot climb to a higher potential energy position than the raised top pedal unless you choose to eject yourself from the bike or in the same manner as the holding onto the handlebars.the leg itself could never cause a wheelie, as it is pushing downwards yet it is the force needed to cause the rotation, it would always be pushing against itself. If the back wheel was stuck in wery strong glue, with a very strong rider in a very easy gear could never rotate the frame around the bike as he could only input the energy of his own weight, , but he could exert energy by trying !

The arms are doing an isometric activity, and thus perform no work.  No extra energy is needed for it.  The work can be measured as force * distance.  You can measure that where the tire meets the road (W_T) or where the leg moves the pedal (W_P) and ignoring friction and such, W_T is equal to W_P, making the process up to 100% efficient.

Energy is expended 8n a contraction, alot like the jaws of an animal, both muscles work against each other., in essecnce the arms are increacing the acceleration felt by the rider over the 9.82 of gravity

[Halc]

I considered the bike and rider to be a single unit, and any internal forces within that unit (leg on pedal, hands on handlebar) have zero effect on the max acceleration the whole thing can do without doing the wheelie.

yep but the efficiency is altered, push your hands together, net zero acceleration, balanced force, lots of energy used ?

No energy used.  You're confusing force with energy.  I can do the same with a C clamp indefinitely without needing to replace the batteries now and then.  If you count the fact that the human body burns calories doing nothing but sitting still, then yes, the human-powered bike or clamp can't be 100% efficient.  I was only counting the work done by the human compared to the work done by the bicycle/human unit.  Chemical engines are typically inefficient.  A steam locomotive is less than 10% efficient for instance, but that didn't stop them from being used.

Technically, a bicyclist on level ground is 0% efficient by definition since at the end of the day, no work was done.  All the energy has dissipated as heat.

Notice also that the dragster could put its center of gravity far further forward, but they design it with the engine and driver all the way in the back.  Doing a wheelie will lose a race, but almost doing one will win it.

the weight is kept as close as possible to the right side of the drice wheel, more useful friction.

I do not know what a 'drice wheel' is, but I cannot see the thing benefiting from the center of gravity being more to the right of something.

As a bicycle rider, I disagree with this.  I frequently exert more force on the pedal than my own weight if accelerating hard.  This can be countered by pulling up on the handlebars (which has no effect on the wheelie) or by pulling up with the other leg.

you can only exert the force of standing on the pedals

As I said above, I can (and do) exert more force than than that, and it would take less force than that so long as force at rear wheel is more than 9.8tanθ n.  That might translate to say only 100n at the pedals, far less than my 800n weight.

you cannot climb to a higher potential energy position than the raised top pedal

Blatantly wrong.  My center of mass is always well above the pedals, and it moves very little while riding, so the potential energy represented by this is essentially not part of the equation.  I never use it.

the leg itself could never cause a wheelie

Then you don't understand the physics at all since all the energy comes from the legs, and sufficient force from the legs would cause sufficient force at the rear wheel to do said wheelie.  And the force at the pedals can be surprisingly low if a low gear is selected.  The selection of gear determines the ratio of pedal force to forward thrust on the bicycle, and that ratio can be anything you want.

, as it is pushing downwards yet it is the force needed to cause the rotation, it would always be pushing against itself.

Those are internal forces which make zero net contribution to the situation.  As I said, all that matters is where the center of gravity is and the force at the rear wheel (and the strength of gravity).

You're essentially asserting that it is impossible for a bicycle to do a wheelie, despite all the evidence to the contrary.

as he could only input the energy of his own weight

Weight is not energy, and weight never comes into play since my body doesn't move up and down significantly as I pedal.
Force at the pedals is what matters, and force there is by no means limited to one's weight, nor does a wheelie necessarily require more force at the pedals than one's weight.
Use the equation I gave.  Do you disagree with it?  It comes from simple force vector addition.  The mathematics is trivial. Given the force required (at the rear wheel), it is a simple calculation to derive the force necessary at the pedals to get that force at the rear, a function of the gear ratio, wheel size, and pedal arm length.

Energy is expended 8n a contraction

Energy is not measured in n.  Energy is force * distance, and since the arms don't move, no energy expended.  The function of the arm could be a rod strapped to an armless rider, making it interesting for him to steer, but a bike steers itself.  I can ride without using my arms, and yes, I can do a wheelie while riding like that, if I like flirting with danger.

[Petrochemicals (OP)]

I considered the bike and rider to be a single unit, and any internal forces within that unit (leg on pedal, hands on handlebar) have zero effect on the max acceleration the whole thing can do without doing the wheelie.

yep but the efficiency is altered, push your hands together, net zero acceleration, balanced force, lots of energy used ?

No energy used.  You're confusing force with energy.  I can do the same with a C clamp indefinitely without needing to replace the batteries now and then.  If you count the fact that the human body burns calories doing nothing but sitting still, then yes, the human-powered bike or clamp can't be 100% efficient.  I was only counting the work done by the human compared to the work done by the bicycle/human unit.  Chemical engines are typically inefficient.  A steam locomotive is less that 10% efficient for instance, but that didn't stop them from being used.

Sorry halc but you as a biological animal ( im assuming here, you may be an electric life form within the internet) you cannot fail to know that pushing on a imovable object takes energy from you, you become hot and tired and therefore must be purpousfully untrouthful. The rest of the answer reads with as much  distruthful content.

[alancalverd]

I was invited to join a group of ecowarriors with a horse-drawn farm. I calculated that a horse exhaled as much carbon dioxide just standing still for a year, as a small car travelling 8000 miles.  Ploughing adds animal cruelty to the inefficiency.

Worth considering the recumbent bike. The maximum force you can exert on a conventional pedal is your own weight, but most people can manage twice that by pushing against a shoulder restraint.

[Petrochemicals (OP)]

I may have got this wrong after looking at a bike again, dont judge, thats why im asking. Very similar anyway. Not much difference between the two.

 The directions of the chain and motion of the pedals mean that the bike is driven down by the leg, driven down by the weight of gravity on the mass, and driven down by the rotation induced in the wheel. I realise the weight of the mass and the force of the leg can be construed as the same thing but the active force of the leg is multi affective, ie rotation driveforce and angular force.

The rider is positioned near the rear wheel I IMAGINE, to minimise the lever force  of the riders weigh on the front wheel driving the front wheel down, rather than friction advantage for the rear wheel, as tye rider is very unlikely to provide enough force to spin the rear drive wheel.

The foot pushes down, the bike accelerates, the mass seeks to remain stationary and this forces a partial lifting of weight on the front wheel. The rotation of the framedown toward the front wheel is countered by the mass of the bike wishing to remain stationary, especially the large mass of the rider, high above the rear wheel in its unstable position. The foot pushing against the pedal is supposed to be in a  neutral balance, only accounting for forward motion.

Thing that strikes me is the foot is providing the counter rotation to the riders unstable position. Unless your input via the pedals is a small fraction of the energy that the bike has in total, the instability of the position of the rider is incredibly problematic and consumes a great ammount of energy. Sort of like the unicycle taking alot of energy staying still, and not much in forward motion. Three points)

1)The closer a bike rider gets to verticaly above the rear wheel (when your going up hill) the worse the instability, thus the leg has to work even harder to push the bike down, this seems the worst case senario as going up hill is the hardest motion and the greatest ratio of energy input to bike kinetic energy

2)As the line of gravity through the rider becomes more parallel to the direction of travel as you go up hill the purchace the leg gets from the gravitational mass of the rider is reduced.

3) as the like of gravity is no longer perpendicular to the motion when going up hill , more of the energy is put into rotation. The rotation of the bike into the floor is a thing i am not sure about. Is this inefficient or not ? Forks must be set at an angle for a reason. If you push a wheel into the floor at an angle less than perpendicular to the motion of travel, what would be the efficiency of this ?


There is also the fact that the leg is connected to the unstable rider, thus the leg is working against itself.

[Halc]

The maximum force you can exert on a conventional pedal is your own weight

My bike allows me to pull up with the other leg, and I just have the cheap rat-trap clips.  The higher-end ones bolt your shoe to the pedal.
But even a flat pedal can be pressed harder than your own weight if you're pulling yourself back down with your hands, which is why many kids come off the seat and align themselves more forward when racing.  Alternatively one can strap one's butt to the seat, but I've never seen that done.

The directions of the chain and motion of the pedals mean that the bike is driven down by the leg, driven down by the weight of gravity on the mass

As I've pointed out above (without a reply from you) weight of the rider is not a limit to the force he can exert on one pedal, but we can go with this limit if you like since this force (even a small one) has no limiting effect on the acceleration of the bicycle. So let's limit that force to the person's weight.

The rider is positioned near the rear wheel I IMAGINE, to minimise the lever force  of the riders weigh on the front wheel driving the front wheel down, rather than friction advantage for the rear wheel, as tye rider is very unlikely to provide enough force to spin the rear drive wheel.

The rider at rest indeed puts more weight on the rear wheel, but the purpose of that is mostly safety, allowing much more braking force to be applied to the front wheel.  If you want to accelerate hard, moving your center of gravity forward is the trick, but only within limits of the traction at the rear.

The foot pushes down, the bike accelerates, the mass seeks to remain stationary and this forces a partial lifting of weight on the front wheel.

Yes.  Simple force vector addition would illustrate this nicely.

The rotation of the framedown toward the front wheel is countered by the mass of the bike wishing to remain stationary

No, it is countered by the road pushing up on the front wheel preventing it from rotating forward due to gravity.  The inertia of the bike/rider would slow that rotation, but not prevent it.  The road prevents it, keeping the bike level at all times.

The foot pushing against the pedal is supposed to be in a  neutral balance, only accounting for forward motion.

Yes.  What else are the feet doing except propulsion?

Thing that strikes me is the foot is providing the counter rotation to the riders unstable position.

Not sure what you mean by unstable position.  If the rider is centered above the pedals, there is no torque on the rider.  If he's off center, the seat (or handlebars) counters the torque.  Either way, I've never seen a rider rotate (relative to the bike) due to pedaling too hard.

1)The closer a bike rider gets to verticaly above the rear wheel (when your going up hill) the worse the instability, thus the leg has to work even harder to push the bike down

No.  If the leg works harder, there is more thrust at the rear wheel and the bike tips backwards.  The closer the center of gravity gets to being above the rear wheel, the less thrust can be applied.  If this isn't enough thrust to maintain pace up the hill, the bike slows.
By moving the center of gravity back like that, you're making θ smaller, and thus reducing the max possible thrust, meaning the rider must reduce force on the pedals to keep the wheels on the road.

this seems the worst case senario as going up hill is the hardest motion and the greatest ratio of energy input to bike kinetic energy

Few hills are steep enough to worry about this, but we're talking theory here, not reality.  Yes, given perfect non-slip surfaces, a rider would need to move his center of gravity forward in order to go up a sufficiently steep hill.  Force on the pedals has no direct effect on keeping wheels on the road since any force downward must have an equal and opposite reaction upwards (Newton's 3rd law) and thus have zero net effect on preventing bike rotation.  That 3rd law can show that all internal forces make zero difference to the max acceleration.  I treat the thing as a black box with a center of gravity and force exerted at 2 points (where each wheel touches the road).

3) as the like of gravity is no longer perpendicular to the motion when going up hill , more of the energy is put into rotation.

Until there is actual rotation, no energy goes into it.  Some of the energy thus goes into gain of potential energy and less into gain of kinetic energy.

The rotation of the bike into the floor is a thing i am not sure about. Is this inefficient or not ?

During normal riding, the bike never rotates.  It has nothing to do with efficiency.  Efficiency is about the percentage of the energy consumed that actually performs work, as opposed to say just lost to heat.

Forks must be set at an angle for a reason.

Stability.  A vertical sraight fork would not let you ride without hands on the bars.

If you push a wheel into the floor at an angle less than perpendicular to the motion of travel, what would be the efficiency of this ?

The front wheel can push from side to side but is incapable of pushing anywhere except straight downward in the vertical plane of travel.  This is not true if the front brakes are applied, which generates a non-perpendicular force vector on the front wheel.

There is also the fact that the leg is connected to the unstable rider, thus the leg is working against itself.

Per Newton's 3rd law, this cannot be correct.  I also don't know why you think the rider is unstable.

[Jeffery21]

The effort that your legs exert on the pedals is transferred to the back wheel by the chain as you ride a bicycle. This force has the ability to do one of three things.

1. Push the bike ahead by rotating the wheel against the surface it is on.

2. Pull the bike into a wheelie by rotating the frame upwards around the pivot of the wheel. This may be seen in the practice of pulling a wheelie, which involves lifting the handle bars slightly and rotating the rear wheel with the pedals, resulting in a simultaneous forward and upward push, resulting in a wheelie. In such a case, the rider's weight may cross the pivot axle of the back wheel.

[Petrochemicals (OP)]

The effort that your legs exert on the pedals is transferred to the back wheel by the chain as you ride a bicycle. This force has the ability to do one of three things.

1. Push the bike ahead by rotating the wheel against the surface it is on.

2. Pull the bike into a wheelie by rotating the frame upwards around the pivot of the wheel. This may be seen in the practice of pulling a wheelie, which involves lifting the handle bars slightly and rotating the rear wheel with the pedals, resulting in a simultaneous forward and upward push, resulting in a wheelie. In such a case, the rider's weight may cross the pivot axle of the back wheel.

I have been over this before. The rotation of the bike is countered not only by the gravity of the rider who is forward of the rotation point, but the force on the pedals. When going up hill the strain becomes evident, much effort yet not travelling much distance, eventually the bike does not move and the rider is static whilst applying force to both pedals.