D
Doug McLaren
- Jan 1, 1970
- 0
| ....
| > | that means for you to make the same output, you would have to
| > | put all your weight on the pedal for 1200/200 seconds or 6
| > | SECONDS!
| >
| > Your understanding of the idea of work (in the physics sense) is very
| > flawed bla bla bla.
|
| I guess you missed the relationship between thrust and time.
No, I understand the relationship. It's just not relevant to figuring
out how hard and long a person would have to work to recharge a
battery.
| Hint: pretend the airplane is just a fancy rocket. In this example
| it is putting out 2 lbs. of thrust, for 600 seconds, we are
| disregarding the weight of the rocket.
You are grossly mangling the physics involved and using that to come
up with absurd answers. This is not rocket science, an airplane is
not a fancy rocket, and when we're talking about charging a battery
with human power, there's no need to involve an airplane.
Hint: I have a degree in physics. I spent several years in school
studying this stuff, though this is _the_ basics, Physics 101. They
go over this stuff in the very first physics class in college, and
probably in high school too (I don't really remember what we covered
there.)
| Yes, you actually have to be moving the pedal with your entire weight for
| those 6 seconds, but with a spring and proper gearing or leverage, you can
| reproduce the same two pound push for 600 seconds.
So, what I really need to do is put this magic pedal under one of the
corners of my bed (so it's supporting much of my weight), and then
take a nap on it. Unlimited free energy! I could put one of these
pedals into an electric R/C plane, wrap it in rubber bands (so there's
a constant force on it) and use that to fly my electric plane across
the Atlantic. Look out Maynard! Look out laws of thermodynamics --
I've got a perpetual motion machine, in R/C form!
| Reaching for the work formula will not help you see this
| relationship without a bit of algebra, and that woud be contrary to
| my stated goal of a quick guess
.
I didn't make a quick guess. I did all the math and algebra involved
(it's not very much, actually -- took a few minutes) and gave you
exact figures (and explicitly stated all the
assumptions/simplifcations I made.) Actually, I used the `units'
program to do most of the heavy lifting for me --
% units
2084 units, 71 prefixes, 32 nonlinear units
You have: 200 pounds-force * feet
You want: joules
* 271.16359
once I had that figure -- 200 pounds * 1 foot = 271 joules, the rest
was just simple algebra and arithmetic. Oh, you'll also need to know
that power = voltage * current (watts = volts * amps), one watt = one
joule/second, that there's 3600 seconds in an hour (to convert volts
and amp-hours to joules) and 746 watts in a horsepower (though somehow
I originally had it in my head that it was 760 watts. Not sure where
that mistake came from ....)
http://en.wikipedia.org/wiki/Mechanical_work may be of some assistance
if you still don't understand the physics involved. Go down to the
`Simpler formulae' part -- there's no need to use integrals to get a
good approximation of the human work needed.
| > | that means for you to make the same output, you would have to
| > | put all your weight on the pedal for 1200/200 seconds or 6
| > | SECONDS!
| >
| > Your understanding of the idea of work (in the physics sense) is very
| > flawed bla bla bla.
|
| I guess you missed the relationship between thrust and time.
No, I understand the relationship. It's just not relevant to figuring
out how hard and long a person would have to work to recharge a
battery.
| Hint: pretend the airplane is just a fancy rocket. In this example
| it is putting out 2 lbs. of thrust, for 600 seconds, we are
| disregarding the weight of the rocket.
You are grossly mangling the physics involved and using that to come
up with absurd answers. This is not rocket science, an airplane is
not a fancy rocket, and when we're talking about charging a battery
with human power, there's no need to involve an airplane.
Hint: I have a degree in physics. I spent several years in school
studying this stuff, though this is _the_ basics, Physics 101. They
go over this stuff in the very first physics class in college, and
probably in high school too (I don't really remember what we covered
there.)
| Yes, you actually have to be moving the pedal with your entire weight for
| those 6 seconds, but with a spring and proper gearing or leverage, you can
| reproduce the same two pound push for 600 seconds.
So, what I really need to do is put this magic pedal under one of the
corners of my bed (so it's supporting much of my weight), and then
take a nap on it. Unlimited free energy! I could put one of these
pedals into an electric R/C plane, wrap it in rubber bands (so there's
a constant force on it) and use that to fly my electric plane across
the Atlantic. Look out Maynard! Look out laws of thermodynamics --
I've got a perpetual motion machine, in R/C form!
| Reaching for the work formula will not help you see this
| relationship without a bit of algebra, and that woud be contrary to
| my stated goal of a quick guess
.I didn't make a quick guess. I did all the math and algebra involved
(it's not very much, actually -- took a few minutes) and gave you
exact figures (and explicitly stated all the
assumptions/simplifcations I made.) Actually, I used the `units'
program to do most of the heavy lifting for me --
% units
2084 units, 71 prefixes, 32 nonlinear units
You have: 200 pounds-force * feet
You want: joules
* 271.16359
once I had that figure -- 200 pounds * 1 foot = 271 joules, the rest
was just simple algebra and arithmetic. Oh, you'll also need to know
that power = voltage * current (watts = volts * amps), one watt = one
joule/second, that there's 3600 seconds in an hour (to convert volts
and amp-hours to joules) and 746 watts in a horsepower (though somehow
I originally had it in my head that it was 760 watts. Not sure where
that mistake came from ....)
http://en.wikipedia.org/wiki/Mechanical_work may be of some assistance
if you still don't understand the physics involved. Go down to the
`Simpler formulae' part -- there's no need to use integrals to get a
good approximation of the human work needed.
