crocomire:

id advice you not to pay any attention to the bickering going on in this thread, which undoubtly hasnt reached its peak yet.

just read everything posted here, and make up your own mind. try and decide what you think will solve the problem at hand in a way you understand, since i doubt youll be getting anything wiser from the differences between mr AP and this community.

the site dmytry linked contains some usefull info btw.

First of all, I really appreciate all the replies!

Quote:
how do you define the amount of energy the biker spends? all chemical energy used in his body? if so, you should first determine which fraction of that is put to use in the muscles involved in riding his bike.

At http://www.cptips.com/energy.htm it is stated that "only 25% of the Caloric energy in the food we eat is actually used to power the mechanical work of the muscle cells"

Quote:
when you have this, then there are the biological inefficiencies involved in muscles. muscles have a certain optimum working speed/force. if you want to do it right youd need data describing the muscles various relations for instance its load vs speed curve. this is crucial if you want to capture phenomena such as a biker not being able to keep pace in low gear at high velocities.

At http://www.tiem.utk.edu/~gross/bioed/webmodules/muscles.html I found the relation between force (P) and speed of contraction (V):
P = (c / (V + b)) - a
a, b and c are constants.

Initially I think I'll ignore this effect.

Quote:
also, i imagine there are some time dependant characteristics. you can put much more force in a single short push, where all muscles can contract according to their optimum, than over a prolonged period of time, such as pushing against a static object, which is accomplished by different muscle strands taking turns in maintaining the force, and getting tired on top of that.

if you cant find any data, we can do nothing more that guess a little. first i suggest you try and find some of it, and when we know in what format it comes, if at all, lets take this a step furter.

For an example, lets just say the muscles of a biker use 100 watt and have an efficiency of 25%.
How do I find from this the force they can excercise? It's still not clear to me if Power = force * speed is appropriate here (but I assume not)

I do not think biker have outside power of 25watts (25% of 100 watts) . It is very small.
Maybe it means that biker produce 100watts of mechanical power (and produce 400 watts of heat).

edit: from link, recreational or biker's mechanical power is like 0.3..0.7 of horsepower, depending to time over what this power is sustained. It's about 223 .. 447 watts. Of course efficiency is around 25% .

And, you can not really find force from there. At zero speed, force will be one, at some other speed, force will be other. Look at that link.

Quote:Original post by Dmytry
I do not think biker have outside power of 25watts (25% of 100 watts)
Maybe it means that biker produce 100watts of mechanical power (and produce 400 watts of heat).

I just made up some numbers...
Lets say the a biker uses q watt in total, from which r watt is used to power muscles. Lets say the efficiency of the muscles is s percent. How do I find the force that these muscles can excercise if I ignore the load/speed curve?

simple answer: you can't.
complex answer: if you talk about force at zero velocity, when you push wall, your muscle efficiency is just 0.

Quote:Original post by crocomire
First of all, I really appreciate all the replies!

Quote:
how do you define the amount of energy the biker spends? all chemical energy used in his body? if so, you should first determine which fraction of that is put to use in the muscles involved in riding his bike.

At http://www.cptips.com/energy.htm it is stated that "only 25% of the Caloric energy in the food we eat is actually used to power the mechanical work of the muscle cells"

thats a start, but its not a very telling statistic, since it doesnt tell where that energy is spent, and for the movement of the bike, were only interested in that spent on the pedals.

Quote:

Quote:
when you have this, then there are the biological inefficiencies involved in muscles. muscles have a certain optimum working speed/force. if you want to do it right youd need data describing the muscles various relations for instance its load vs speed curve. this is crucial if you want to capture phenomena such as a biker not being able to keep pace in low gear at high velocities.

At http://www.tiem.utk.edu/~gross/bioed/webmodules/muscles.html I found the relation between force (P) and speed of contraction (V):
P = (c / (V + b)) - a
a, b and c are constants.

Initially I think I'll ignore this effect.

good you found it.

Quote:

Quote:
also, i imagine there are some time dependant characteristics. you can put much more force in a single short push, where all muscles can contract according to their optimum, than over a prolonged period of time, such as pushing against a static object, which is accomplished by different muscle strands taking turns in maintaining the force, and getting tired on top of that.

if you cant find any data, we can do nothing more that guess a little. first i suggest you try and find some of it, and when we know in what format it comes, if at all, lets take this a step furter.

For an example, lets just say the muscles of a biker use 100 watt and have an efficiency of 25%.
How do I find from this the force they can excercise? It's still not clear to me if Power = force * speed is appropriate here (but I assume not)

well, this is appropriate here, but its not as straightforward as you might think.

both power and force vary heavily with time. the 25w you assume is a time average, and you should realize it isnt applied continiously, but in pulses. also, the transmission ratio between you muscle and your wheel does not only vary with gear, but also with the stance of your legs and pedals. so it boils down to the problem of both power and force being unknown yet related, so this one single relation does not provide enough information to solve the problem. well have to find another relation for them, but it wont be as easy as the one we already have.

all in all its quite complicated, and it probably comes down to making good decisions on where to simplify.

to answer those questions, id like to ask you: you mention a 'bicycling simulation', but what precisly do you mean with that? what does it need to do, what does it not need to do?

Quote:Original post by Dmytry
simple answer: you can't.
complex answer: if you talk about force at zero velocity, when you push wall, your muscle efficiency is just 0.

But to me it seems there is a relation between the energy used and the force excercised: if I push harder on the wall I spend more energy. Howver in this case the power is 0 (because speed is 0).
I think I'm confused because the power in power = force * speed is expressed in Watt. The energy that is spend during the pushing on the static wall can also be expressed in watt's, but they are not the same.

Maybe, I should read some basic physics book first...
Any recommendations? (I have read the article form the link you provided but I do not understand everything)

Quote:Original post by crocomire

Quote:Original post by Dmytry
simple answer: you can't.
complex answer: if you talk about force at zero velocity, when you push wall, your muscle efficiency is just 0.

But to me it seems there is a relation between the energy used and the force excercised: if I push harder on the wall I spend more energy. Howver in this case the power is 0 (because speed is 0).
I think I'm confused because the power in power = force * speed is expressed in Watt. The energy that is spend during the pushing on the static wall can also be expressed in watt's, but they are not the same.

Maybe, I should read some basic physics book first...
Any recommendations? (I have read the article form the link you provided but I do not understand everything)

Yes, read some physics books.

In case of living being pushing wall, this stuff is biological, bio-physical, and bio-chemical [grin]. There's no general rule.(except, of course, that all energy that is "spent" is just converted to heat, but I suppose you already know that) For example, you can put spring that push at wall. It will push, but will not "use" any energy. Everything depends to what pushes.

Some examples with robots, for better understanding:
Some robot could just lock his manipulators in position that pushes wall, and shut down motors.
Other robot without this ability would have to pull current through motors to push wall, and electrical energy would be converted to heat in the wiring of motor.
Third robot could have superconducting motors, and he again can push without draining his batteries, and in ideal case could have power=force*velocity.

And another robot could use hydraulics, and pump is just shut down when pressure difference is maximal for pump. If he stays still and pushes wall, he spends no extra power, but if he pushes wall with one hand and moves other hand without much force (both hands powered with same pump), he will have to spend more power to sustain unnecessary pressure, more than would be if he wouldn't push wall and would just move other hand.(again, all energy "spent" is converted to heat)

It's all simplified examples, but them shows that it all depends to construction of thing applying the force.
These robots would have different misconceptions about physics...

[Edited by - Dmytry on June 13, 2005 10:26:32 AM]

Quote:Original post by crocomire
But to me it seems there is a relation between the energy used and the force excercised: if I push harder on the wall I spend more energy. Howver in this case the power is 0 (because speed is 0).
I think I'm confused because the power in power = force * speed is expressed in Watt. The energy that is spend during the pushing on the static wall can also be expressed in watt's, but they are not the same.

Maybe, I should read some basic physics book first...
Any recommendations? (I have read the article form the link you provided but I do not understand everything)

Of course you are confused and if you keep reading the nonsense these people are telling, you will be even more confused.

If you push against a wall there is not mechanical work. But there is energy lost, the reason it does not make sense with this mombo-jumbo explanations you are been given, is that you do not have the complete law.

Like I said Thermodynamics say that the total energy lost I equal to the Heat minus the work. So when you push against the wall the wall do not move so no mechanical work, but your temperature rises therefore there is a lost of heat that is explained by that wonderful first law. The problem is all physical contrary to what you have been let to believe.

You finally reach to a sensible conclusion you should read a text book that explain these ideas to you, and forget about all this Confucius’s or Plato’s tactics or reverting everything back to you. Believe me it is not magic it is all just mechanics.

Quote:
to answer those questions, id like to ask you: you mention a 'bicycling simulation', but what precisly do you mean with that? what does it need to do, what does it not need to do?

I would like to simulate a realistic cycling race. In the end I'm only interested in the position, speed and acceleration of each runner at particular points in time. My idea was to give each runner a specific amount of energy and a maximum rate at which this energy can be spend. Each runner has an AI that decides how much energy to spend at each point in time based on a number of factors (how much energy is left, what is the slope of the track, how far until finish, where are the others runners). For example, if a runners decides to break free from the others he increases the amount of energy spend.
Therefore I'm looking for a relation between energy spend per time unit and the speed of the runner. I'm aware the reality is rather complex, but maybe I can use a simple approximation. Maybe I can think of the runner as a simple engine: full (food) goes in and force comes out.