Quote: Original post by crocomire
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.

If you know the power the cyclist puts into the pedals and you know the speed of the bike, just use the force=power/velocity relation to get the force driving the bike forward. Add drag/friction/gravitational forces to get the net force accelerating the bike. I think that would be simple and accurate enough for your needs.

Hello crocomire, I think I can be a bit helpful in clarifying some concepts. So you know that Power is porportional to velocity and force, when you push agaisnt a wall there is in fact power which can also be stated as the rate of change of work : dW/dt. dW = F · dr, in the micorscopic level we see that there are infact corresponding deformations and bidirectional continuous exchanges in momenta between our interacting particles. What we see as everyday pushes and pulls are in fact no more than electrical interactions.

The concept of work does have interesting implications, when we have zero displacement we have zero work, for example, If I exert a large force and pick up a 400kg box to a height of 2m and walk 4m forward and then backward and then dropped the box I would have done no work. It can also be shown that work is a form of energy, in fact all this leads to an interesting tidbit: we have that W = ∫F · ds, W = ΔE then the observation that an escalator uses more energy when people walk up it than when they stand still is not suprising at all. You can read the Feynmann Lectures on Physics Volume 1 for more understanding of these concepts.

That said, a good biker produces about 0.167 ~ 0.11W200 - 300W per pedal. That, coupled with the equation P = F · v should get you a good way towards where you wish to go. If you have more questions please post. I hope that proves useful.

[Edited by - Daerax on June 14, 2005 10:57:59 AM]

Also, the average human consumes energy, ΔE 8 * 106J (2,000 calories) a day and converts almost all of this energy into heat. Per stride a human uses about 20J. Thought I'd add that as well. I am not quite clear what it is you wish to do but you could use this, in addition to the earlier stated stuff, to estimate your energy-force idea. Good luck.

Quote: Original post by crocomire

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.

ok we can work with that.

lets look at the bike as a whole, and the external forces that work on it. three main forces can be recognized: drag, gravity, and contact forces. the contact forces however do no work since they are peripendicular to the direction of motion (or so i shall assume)

just add the gravity and drag vectors, and dot the with your speedvector to find the change in kinetic energy of the biker. add to this the amount of energy the rider is putting on the pedals (you could apply it continiously or in pulses as the rider puts down his feet), and you have the change in kinetic energy per unit time, from which you can derive all other desired quantities.

if so desired you could later add in a more realistic model of the internal workings of the bike(r), ie transmission in relation to the force/speed graph of human muscle. dmytry's link provides plenty of info to get you started there.

also, you could consider more realistic models of human energy troughput. we store a little quickly available energy in our muscles, which gets resupplied relatively slowly by the liver breaking down fats etc into sugars for use in muscles.

Quote: Original post by Daerax
the observation that an escalator uses more energy when people walk up it than when they stand still is not suprising at all.

No matter if some man stands still or moves with constant velocity, force f on escalator is constant until he is on escalator. Energy spent by escalator can be expressed as force*speed*time where speed is speed of escalator and time is time while this man is on escalator. Walking man will be on escalator for less time.

So if we disregard effect of accelerating and slowing down (I think you'll agree that for long escalator, them will not matter), less energy is spent when time is smaller, that is, if this man walk.

I of course consider energy escalator spends to move N people up, and of course assume that that walking (with somewhat variable load) does not increase average friction of elevator.

Quote:
You can read the Feynmann Lectures on Physics Volume 1 for more understanding of these concepts.

That said, a good biker produces about 0.167 ~ 0.11W per pedal. That, coupled with the equation P = F · v should get you a good way towards where you wish to go. If you have more questions please post. I hope that proves useful.

you probably meant 0.11 horsepower.
0.1W it's very small power, around lifting of 1kg to height of one centimeter per second. I probably pull lot more when typing this message.

\Nope, I just crosschecked the units, twas watts. Dont forget we're talking averages here. It could vary anywhere from .35 to .10W. As for the escalator, I believe it was a flat one, so my bad on that. Ill try and see if I can dig up the reference/paper to the study that showed that walking on a moving escalator causes it to use more energy.

[Edited by - Daerax on June 14, 2005 10:59:53 AM]

Maybe real world escapator uses more power because of some strange inefficiencies, but definately not for reasons you told about. Maybe some issues with balance of energy obtained from escalator that moves down (assuming it gives out energy at all) and energy consumed by escalator that moves up.

Quote: Original post by Daerax
Nope, I just crosschecked the units, twas watts. As for the escalator, I believe it was a flat one, so my bad on that. Ill try and see if I can dig up the reference/paper to the study that showed that walking on a moving escalator causes it to use more energy.

as long as you dont accelerate on the escalator it shouldnt matter, and <1W is indeed very little. humans as a whole use 100 as a rule of thumb. .1W gets you nowhere.

You know the ones in airports? That you run back and forth on them as a kid (or still do, if you're like me) agaisnt the direction they are going? Anyway there's no point in my arguing such, Ill see if I can find a reference to the paper.

Quote: Original post by Eelco

Quote: Original post by Daerax
Nope, I just crosschecked the units, twas watts. As for the escalator, I believe it was a flat one, so my bad on that. Ill try and see if I can dig up the reference/paper to the study that showed that walking on a moving escalator causes it to use more energy.

as long as you dont accelerate on the escalator it shouldnt matter, and <1W is indeed very little. humans as a whole use 100 as a rule of thumb. .1W gets you nowhere.

maybe he mean KW?
Really, 0.1W it is approximately equivalent to lifting of 1KG vertically at speed 1cm per second.

on more serious note, visit this link

Quote: Original post by Daerax
You know the ones in airports? That you run back and forth on them as a kid (or still do, if you're like me) agaisnt the direction they are going?

I were thinking about escalators in
a: large shop with more than one floor,
b: subway aka underground, especially Moscow subway.[grin] These ones lift you for tens meters vertically(there are opposite ones that move you down), (that underground is more of anti-nuke bunker than underground.)

Quote:
Anyway there's no point in my arguing such, Ill see if I can find a reference to the paper.

heck.