On Mon, Apr 15, 2013 at 2:01 AM, David Roberson <dlrober...@aol.com> wrote:
> On Sun, Apr 14, 2013 at 7:41 PM, David Roberson <dlrober...@aol.com>wrote: > >> If you are referring to my statement about the magnet and steel, I am not >> confusing them. The force being applied to the steel is attempting to make >> it come into contact with the magnet. Energy is being released by the >> magnet as it draws the metal closer since it is having to work against my >> resistance to that motion. It would be possible to measure the amount of >> energy by attaching a force measuring scale to the steel part and slowly >> allowing it to come into contact with the magnet. You would be able to >> integrate the force times distance curve and obtain the energy. >> >> > >Does the magnet do work (use energy) when you are holding the steel at a > fixed distance from the magnet? > > No, if the steel is held steady then no work is being done by > definition. Work equals the integral of force times distance moved. Work > was done when the steel was moved from far away to the fixed position. > > You did work removing the steel. > >When you let go of the steel and the steel accelerates towards the > magnet, is the magnet doing work on the steel's inertia? > > The magnet is doing work on the steel as it accelerates toward it. > Magnetic potential energy is being converted into kinetic energy in this > case. This is much like work being done on a mass that is moved within a > gravitational field. The same equations apply which is work(energy) equals > the integral of the force times the distance moved. This assumes that the > force has a component that is along the path the steel follows in space. A > force that is always applied at right angles to the motion does no work > upon the object. This would be similar to the motion of a charged particle > traveling within a static magnetic field. No work is done in that case. > > This is correct, but for 300+ the natural forces have been seen as natural because they are not suppose to need a supply of energy to do work (unlike animals and people). So in this view the magnet does work on the steel but it does not need energy to perform that work. This all goes back to the Cartesian notion that God set the universe in motion and only God can destroy or create motion. In fact the CoE was advanced by James Joules in the middle of 19th century to further enshrine the inviolability of the natural forces. Without the doctrine of CoE reasonable people could still entertain the possibility that momentum can vanish from friction. Harry
