Re: [Phys-l] non-conservative --> non-grady ???

[John Denker <jsd@av8n.com>]

On 02/20/2008 11:23 AM, Steve Highland wrote:

> How would the analysis be different if instead of having an electric field
> accelerate a charge we had a fast moving conveyor belt between the plates
> that grabs onto a crate that's delivered through the hole on the left so
> that friction does the work of getting the crate up to exit speed?
>
> I'm imagining the belt going so fast that the crate is slipping the whole
> while as it travels in the area between the plates.  What I'm after is what
> the difference is when the force doing the acceleration is a nonconservative
> one like friction compared to a conservative one like an electrostatic
> force.

Well, I've been claiming all along that there isn't a profound
difference.  A force is a force.  The particle being accelerated
doesn't much care whether the force is grady or non-grady.  In
particular, the work/KE theorems don't care whether the force is
grady or non-grady.

Most importantly, our notion of conservation of energy doesn't
distinguish between grady and non-grady forces.  Both are required
to uphold conservation of energy, no exceptions.