new wave sweeping the nation

March 2nd, 2006
  • trying to lift off with the flaps on
  • sprinting in knee deep water
  • walking in quick sand
  • drag racing with the hand brake on
  • playing tennis at the beach

What else can you think of that approximates the sensation of biking in wind? The whole concept of a vehicle on wheels is that you apply energy to the system, whereby the mechanism propels that into kinetic energy, which yields momentum (the product of velocity and mass). Once momentum is obtained, friction permitting (air resistance included), it will allow the vehicle to travel at constant velocity indefinitely. In ideal conditions, friction is such that a bicycle will slowly decelerate, at a rate of [negative] acceleration a fraction that of the [positive] acceleration, which set it in motion in the first place. In English, that means you pedal hard for 10m and you roll for 60m or 100m. Now, in the case of wind, especially wind hitting you from the front (actually, speaking in terms of aerodynamics, it may be the case that diagonal wind [from the front] is trapped by a greater area of body, which imposes greater friction), the obtained momentum will decrease more rapidly. The result is that the energy applied yields much smaller gain in terms of motion. Now, in a psychological context, this breaks with the assumption that biking is an efficient process, thus causing trauma. See, the beauty of the wheel is that of playing on dynamic friction (which is much smaller than static friction). Ie. it takes more effort to set something in motion than it does to sustain that motion. When you're walking, taking one step will get you exactly one step forward. If you push a big rock forward, it will go forward exactly the distance you push it. But if you push a shopping cart in the supermarket, it will roll on wheels and travel much further than a rock to which you apply the same amount of energy (try this experiment next time you go shopping, it's very instructive!). Let's repeat: dynamic friction. But in conditions of strong wind, the magnitude of dynamic friction approaches the magnitude of static friction, rendering biking no more efficient than walking. Of course, it never actually happens that these two quantities take on the same magnitude, but consider that when walking the energy applied is proportional to your mass. But when biking, you are also moving the bike itself, so it actually takes more energy. When you then experience strong dynamic friction, the benefit of being on a bike falls away, rendering the whole experience very traumatic.

Goddamn flat land. Put up some mountains to trap the wind already!

As an exercise for next week, perhaps you could figure out why stopping at traffic lights at every intersection is greatly traumatic and impeding to the concept of biking?

Finally, if you think all of this theory sounds somewhat familiar, you may suggest the possibility that it is simply high school physics, in which case you would be absolutely correct. And that leads me to a big shout out to Nawaf, who is currently learning all this fascinating material by way of a nice booklet of physics formulae and a calculator to compute all these exciting quantities.

:: random entries in this category ::

7 Responses to "new wave sweeping the nation"

  1. erik says:

    Goddamn flat land. Put up some mountains to trap the wind already!

    Mountains don't trap winds; they force them to change directions, and through other elements involved, moutainous terrain is full of drafts and hurl winds. The same movements of air can be observed in the vicinity of sky scrapers. The science of building sky scrapers actually has an aspect in it where the scientists research whether or not the height and shape of the building will create such strong drafts that they would knock pedestrians walking in the vicinity of the building right off their feet.

    Next time: take a bus, Einstein ;)

  2. numerodix says:

    That is so uncool. It's pretty obvious that I couldn't come up with a good punchline, but you didn't have to do that.. :lazy:

    Though flawed as the rationale may be, it's not exactly an anomaly to say that NL is exposed to a lot more wind than say inland Norway. Reason being the flatness, on the Norwegian coast you get winds like a mofo, but inland it's much quieter. Hell, Denmark = wind turbines, that's no coincidence. And Utrecht is pretty damn far inland.

  3. erik says:

    Utrecht is perhaps 60km inland, how is that far? :D

    And jet streams as well as continental influences make our climate very windy on average. That has little to do with the flatness of the land. I just wish I could remember the exact terms... hmm...

  4. ash says:

    Interesting physics lesson, but you forgot a few things. For example, although the bike has extra mass which takes extra energy to accelerate, it also means it's harder for the wind to slow you down.
    Also, if a cyclist and pedestrian are moving at the same speed than their wind resistance will be the same...assuming an equal effective frontal area. I'm not sure who would have the bigger area but I'd guess the pedestrian would.

  5. Diana says:

    Well, what can I say...I know it sucks to have wind that hits you from the front... I used to curse that stupid wind almost every single day when biking to school. I was almost never lucky, somehow I never had wind that hitted me from the back, that would have made my life a lot easier at the time.

  6. numerodix says:

    [3] 60? That's it?? omigod.

    [4] (1) Yes, but nevertheless it is the case that far more energy is wasted, which is really all I set out to demonstrate. The precise margins are not really important.
    (2) This is irrelevant, noone would bike at the same speed a person would walk, for one thing that creates a balance problem because the motion is too slow, secondly where is the benefit? The effect I tried to describe is different, that of quick acceleration, the deceleration. As compared to walking, which is fairly constant speed.

  7. ash says:

    [6] Hang on...I thought your point was that the wind slowed you down to the point where you were moving at the same speed as a pedestrian. If that isn't the case then surely cycling is still better than walking? And comparing walking to rolling is always going to be difficult...walking "dissipates" kinetic energy fairly quickly because it's an inefficent way of preserving momentum.
    Also, walking is much more analagous to quick acceleration and deceleration, as each step is a push i.e. a force, which is applied repeatedly. Cycling is usually a constant rotation which gives a fairly even force.

    My main point in all the above is that I'm not convinced by your demonstration.