noob

My opinion? The definition of the term Coulomb force has rarely, if ever, be questioned. Its found in all textbooks on electrodynamics. The mathematical expression for it is given in Eq. (1) at

 

http://scienceworld.wolfram.com/physics/CoulombForce.html

 

Pete

This is exactly the problem. You don't know what a coloumb force is. What you mean and what you post is the law of coloumb, not the comoumb force of friction!

No, I did address that in my post. If you don't have the tire spinning, then you have a sled with wheels rather than a bicycle, as I said. And this problem is about bicycles, not sleds. The bicycle will have some of its energy transferred into rotational kinetic energy, in addition to translational kinetic energy for the entire bicycle plus rider. This will have a lower effect on the heavy rider than on the light one, so that without friction the heavier rider will still win. And no, I don't care what makes the tires spin, so long as they do spin at the appropriate rate.

This is wrong! You will never have a rotation if there is no friction and you don't have rotation energy! Rotation energy coul only exist here if you have friction.

Even if you ignore friction, the heavier guy will win the bike race. Unless you replace the bike with a sled, the bike wheel has to rotate as well as translate. Then a lesser portion of the energy of the heavy guy will be wasted in rotating the bike wheel, so that the heavier guy will win anyways.

No, think about the dynamic of a tire. You haven't got a rotation and no raotaion energy because of no friction. Only potential energy which transforms to kinetic energy and the mass cancels out.

@Pete:

I guess you missunderstood me. Tell me what is the coloumb force in your oppinion?

greetings

Hi Pete,

Not if the person asking the question wishes to ignore things like friction and drag.

If the person wants to ignore the friction, the mass cancels out! This follwos directly of the conservation of energy. It is correct because the system is conservative. The dissipative friction force is zero. Without friction the two riders are simultaniously in the finish. If you have friction the structure of the surface is important to say something about the situation.

 

No. The acceleration of a body is dependant on the coeffiction of kinetic friction but is independant of mass.

 

think about this sentence. It is completely nonsense

What is [math]\vec{F}_{r}[/math]? I.e. what does the "r" subscript denote? If this is simply the force on the body then once you replace it with ma you will see that the mass drops out yet once again!

Oh, sorry. It thought in German. We have not the same indecis in German. The "r" stands for "Reibung" which is the German word for friction.

When we talk with Newtons arguments, this is the friction force. Such things like energydissipation are only useful, if we want to build Euler-Lagrange or Hamilton functions what the creator of the thread probably doesn't want.

 

What is a "trem"?

This is a typo I meant "term"

 

I disagree. Consider a body sliding on a surface under friction for which the coefficient of kinetic friction is [math]\mu_k[/math]. Then

 

[math]F = ma = \mu_k F_n = \mu_k (mg) [/math]

 

Cancel out m to yield

 

[math]a = \mu_k g [/math]

 

This is also completely nonsense! What you wrote is a coloumb assumption, but we are talking about sliding.

 

Huh? What does that mean?

 

It means that sliding in a bobsled run is better than sliding on a street. This is the fundamental argument of dissipative motion on a real surface like the street or the bobsled run.

greetings

Hi,

the small guy with 50 kg would win the race!

If we talk about such exercises it is very important to look on the undergound. In an ideal case the mass is completly unimportant. The mass fall out and so it don't cares. 100 kg, 150 kg, 2000kg, no matter. But it is not ideal. We have friction and becaus of that the friction force is directed against the motion. If you look now to wintersports, the mass could be useful, because it melts the ice and snow and the friction coefficient becomes better, but on a street is more mass not good.

[math]\vec{F}_{r} = \mu \vec{F}_{n} = \mu m \vec{g} \cos(\alpha)[/math] This trem slows the fatter guy down and the surface of the street wouldn't melt for a better friction coeffizient.

greetings

You know you can preview your post right ?

yes, but often it is very useful to save such things

In example solving a differential equation with Laplace is something where it is quite useful if you saved a Lapalce correspond like in my example in the first post and it is easier to check it out here and you could even edit it later and copy it to an actual post.

This are advanteges of posting and trying Latex.

greetings

Hi,

I used the search function but it looked as if such a Thread didn't exist until yet

This is a test Thread. It is for testing Latex

[math]f(t) \circ\!\frac{\qquad}{\qquad}\! \bullet \mathcal L \lbrace F(t)\rbrace[/math]

Threads for testing are cool [math]\heartsuit[/math]

greetings

[math]\text{this is a test}[/math]

fine, it works

Hello

I am the noob. In real life people call me Adrian. I am from Freiburg, which is a town in the south of Germany. I am studying physics at the Albert Ludwigs University. Until yet I was very active in certain German forums, but I am on a point in my education, where I have to say, that english is such an important language, that I decided to change in an english forum for learning science in english.

I want to say sorry for grammer mistakes. I am working and learning for better grammer. In the fall I will visit english courses and I hope it will change the problems.

In this case for wirting good posts and Threads

greetings

Adrian