Conservative Force: Is F Dependent on Velocity?

[johann1301]

If F is a force acting on a atom and is dependent on the velocity of the atom. Is the force conservative?

 

[jbriggs444]

What do you think -- what is the definition of a conservative force?

 

[gleem]

Velocity dependent forces are generally not conservative and exception is the Lorentz force due to a magnetic field acting on a charged particle although some would strictly speaking not consider this force conservative either.

 

[johann1301]

Lets say

F=-av

If i integrate this, isn't it soley dependent on the start and end point? And thus, its conservative..?

 

[johann1301]

a is just a constant.

 

[gleem]

V is dependent of time since v = a*t = m*a. Isn't it clear therefore that the work in reaching a specific position will depend on the path traveled. The longer the path the more time and thus more work.

 

[gleem]

my a is the acceleration due to the force

 

[Dale]

Lets say

F=-av

If i integrate this, isn't it soley dependent on the start and end point? And thus, its conservative..?

Certainly not. Consider $a=-1 \; N/(m/s)$ and an object which goes out a distance of 1 m at 1 m/s and then back at 1 m/s and another which goes out the same 1 m distance at 1 m/s and then back at 10 m/s. The force does 2 J of work for the first path and 11 J of work for the second. Furthermore, the work is non-zero, so both differ from the path which just stays at the endpoints.

 

[DrStupid]

Velocity dependent forces are generally not conservative and exception is the Lorentz force

... or any other force always acting perpendicular to velocity (e.g. coriolis force).

 

[audire]

Are you asking if force is always conserved? From my understanding yes f=mv thus it will always equation out to your mass and velocity on the other side of the equals sign?

 

[jbriggs444]

Are you asking if force is always conserved? From my understanding yes f=mv thus it will always equation out to your mass and velocity on the other side of the equals sign?

That is not at all what is being asked.

A force is "conservative" if the work done on an object by that force as it moves along any path that loops back to where it started is always equal to zero. Note that in this context we are talking about a force "field" as in http://en.wikipedia.org/wiki/Field_(physics)