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Author Topic: Why can I cycle faster than the fastest runner runs?  (Read 14098 times)

Offline Geezer

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Re: Why can I cycle faster than the fastest runner runs?
« Reply #25 on: 02/05/2012 02:07:39 »
Bluedy 'eck! It can't be Groundhog Day already?
 

Offline David Cooper

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Re: Why can I cycle faster than the fastest runner runs?
« Reply #26 on: 02/05/2012 20:26:29 »
Well, here's a compact version of the answer for those who've come to the party late. If you're on a bicycle, you can take a complete rest while still moving at speed, but if you try doing that while running you'll have a nasty crash into the tarmac. Runners have to work hard even to run slowly, whereas cyclists don't.

That's probably also why far more people drop dead while out jogging than do when cycling - you have to stop moving to have a proper rest if you're out for a run, but there's a psychological pressure on you to keep running no matter what, so you slow down rather than stopping and you fail to recover as quickly as you could, and may even continue to do the damage that will take you out. The cyclist has it easy - (s)he can keep going at a respectable speed while reducing the energy output to just a few percent.

So, you're comparing two very different activities - one involves high power all the time, while the other allows you to do a little work to get up to the same speed as the runner and then to coast along. Think about running downhill and you can see that the runner still has to work hard while the cyclist has no work to do at all. On steep uphills, the runner eventually gains an advantage, but it has to be steep.
 

Offline Geezer

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Re: Why can I cycle faster than the fastest runner runs?
« Reply #27 on: 02/05/2012 21:57:47 »

one involves high power all the time, while the other allows you to do a little work to get up to the same speed as the runner and then to coast along.


"High power all the time" - Power is really instantaneous energy consumption, so presumably you mean high energy all the time.

The energy consumed can do two things. It can do useful work (moving you from A to B) or it can be dissipated into the environment in the form of heat. The efficiency of the "machine" is the ratio of the useful work to the total energy consumed.

We can't really alter the efficiency of the human body, but the bicycle clearly improved the efficiency of the overall machine (if you allow that the two cases are examples of "machines").

The only way you can improve the efficiency of a machine is by reducing friction.
« Last Edit: 02/05/2012 21:59:31 by Geezer »
 

Offline Geezer

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Re: Why can I cycle faster than the fastest runner runs?
« Reply #28 on: 03/05/2012 00:50:23 »
I was going to add that "a bike only improves efficiency by reducing friction which allows us to muck around with gearing ratios", but there is a bug in the forum software that won't let me turn off bold once I have turned it on :)
 

Offline hiseri

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Re: Why can I cycle faster than the fastest runner runs?
« Reply #29 on: 11/11/2013 18:50:53 »
I know you all had this discussion two years ago, but it came up near the top of my Google search.

Someone mentioned the upward force exerted when running. I think that's the most important issue. When you're running, you need to apply a force to the ground that propels you forward and upward (so I guess you apply a force backward and downward). On a bike, this happens where the wheels contact the ground, but the upward/downward force is taken care of by the rigidity of the bike frame and wheel, and so almost all of the energy you put into the pedal goes to propelling you forward. On the other hand, since running on a treadmill is not much easier than actually running, the propulsive part of running must not use a lot of energy, and so maybe it really is a matter of gearing.

By the way, if you remove the aerodynamic drag of riding a bike, you can go really fast. Bikes with fairings can do 70mph+, I believe, and bikes drafting a car can do 120mph.
 

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Re: Why can I cycle faster than the fastest runner runs?
« Reply #29 on: 11/11/2013 18:50:53 »

 

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