| Thanks, Joe. Your formula does, indeed, give the distance the surface
of the wheel travels. For example, when I calculated my "mph" at
60 rpms, the result was 2.5 mph. Well, the speed of the wheel may
have been 2.5 mph, but I know that if I was on a real bike, I would
have been moving a lot faster than a slow stroll with that much
effort.
I called the company (Voit) and they told me to set the odometer
to "0", then ride for 1 hour. ("Yeah, sure thing, pal!")
Logically, the change in mileage would equal the mph. I recall
doing this for half an hour once at around 60 rpms. I think I came
to somewhere around 20-30 mph, which sounds about right.
How can I use the formula Joe gave me to calculate the force?
Any physicists out there? (I wish I had paid more attention in
class!)
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| One way to check the force you're using on a stationary bike is
by using a simple spring balance, such as you may well already have.
With the bike tension set to something you're comfortable with, hook
the balance onto one of the pedals and pull, keeping the spring
at right angles to the pedal shaft. When the pedal starts to move,
the spring balance will read (in pounds weight) the "force" you
are exerting when riding (actually a little more, because the
friction on the wheel when in motion is slightly less than that
when stationary).
Then, if your bike is of the low tech. type, like mine,
and you're _really_ keen on the maths/physics of the thing:
- convert the spring balance reading to force in newtons, by
dividing by 2.2 (to get Kilograms weight), then multiplying
by 9.8 m/s^2, the acceleration due to gravity:
- count the number of revolutions of the pedals whilst you're
exercising (that's the really tedious bit, but you can probably
relate it to the odometer reading with a bit of experimentation)
- multiply (number of revolutions) by (pedal shaft length, in meters)
and by 6.28, to get the distance your feet travel
- multiply that distance by the force, in newtons, giving you your
actual energy (strictly, "work") in joules
- Finally, divide by 4180 to give yourself a depressingly low number
of dietary Calories, equivalent to your exercise!!!
The Good News is that the body is a vastly inefficient machine,
so even though you'll only appear to use a few Calories, your muscles
actually burn far more than that providing you with the energy to
pedal away.
Anyway, the above is more for mathematical amusement than anything
else. As Mike says, your heart rate is a pretty good indicator of
whether or not you're exercising at an appropriate rate.
- brian
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Thanks, guys. I hope you don't mind if I use the heart rate method.
Physics experiments were never my cup of tea, but your description
of how to measure the force and calculate Kcals is fascinating
nonetheless. As I said, I wish I had paid more attention in class.
;^)
This brings to mind another question, which I think I'll address
in a new topic...
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