Hi All

I have problems regarding work energy and gravity which I dont get and need some help with to understand. I think I have managed to tie down something here which doesn't quite add up at least not in my own understanding of how forces work but I hope someone can tell me why I'm wrong.

I was taught doing a-level physics that a magnet hovering above another magnet but totally stationary is not a form of perpeptual motion. This is because no work is being done so no magnestism is being used. Does this mean that if the magnet was moving about because it was attached to a simple mechanism such as a piece of string and motor the magnetic field would start to drain away? Now I think most knowlegdable people would answer yes to that question and I do too but that leaves me a big problem with gravity.

You see either gravity must be a form of ever lasting energy or when work is done its strength must deminish. As far as I can tell it has to be one or the other as there's only two choices. So we have our little experiment but we replace the magnets with the Earth and a 100g weight. The weight moves about so its techincally doing work. What happens with the strength of graivty in this situation? Does the weights weight deminish over time or even increase?

Please help me sort this mess out.

I hope you understand that Gravity is the least powerful and most not understood of the four forces making up our Universe. To this day science dose not know if Gravity is a wave or a particle. So comparing it to Magnetism may not be a fare test. Different forces, different principles would apply.

True, but if the ideas about gravitrons are right then the weight should become lighter or there is an infinite energy source there.

Oh, I agree. When ever or who ever learns the True Nature of gravity and learns to manipulate it, will have found the HOLLY GRAIL for energy production, space travel, and a lot of other thing. It,s just not evaluable to you and me now.

Even the Electro Magnetically charged Plates that cancel out gravity in the laboratory's require so much power that at this time large scale use is prohibited. But I have goggled anti gravity and scientist are working on it. Man will get it.

I don't know of this cancelling out experiment. What is it called?

do you think that the same laws of physics aply to gravity?, like when a + and- sides of a manet attract and 2 +/- sides repel, can the same rule aply with gravity in that situation?

Gravity only seems to attract as far as we know. If it does repel we haven't discovered it yet although they are working on that with planned anti-matter experiments at CERN.

Not all movement implies work is being done and even when it does, that doesn't answer the question of what's doing work on what. But even when a gravitational field does work on something, that doesn't alter the gravitational field itself (i.e. the mass generating the field isn't changing).

We are only dealing with the gravity field from the small mass as measuring any change in the Earths would be a monumental task. (The small mass has a gravity field too although it is a small one)

You say work done by a grvaitational field doesn't alter the grvaitational field. Can you show me why?
How does it maintain itself if this is the case as this makes it an every lasting energy source?

A mass sitting in space will generate a gravitational field. But since gravity is a conservative force (and we're really only interested in energy here, anyway), we can stop thinking about forces and instead think of a different kind of field: a scalar field called the gravitational potential field. This field goes to zero the further from the mass you go and gets increasingly negative the closer you get to the mass that's generating it. Wikipedia has [ur=http://upload.wikimedia.org/wikipedia/commons/d/d9/GravityPotential.jpg]this nice picture[/url] of what this looks like. Other masses tend to slide down the potential field (i.e. go from further to closer) and in doing so they pick up some kinetic energy (i.e. work is done on them).

The potential field itself, however, is not changed when something slides down (it depends only on the generating object's mass and the distance from it). It isn't flattening out or eroding in some way. Smaller masses in the field have a certain potential energy just because they're in the field (this depends on both the field itself and the little object's mass; you get it by multiplying the two together) and if they move around in the field there will be changes in their potential and kinetic energy. But energy conservation isn't violated, the total energy remains the same. So when an object falls in a gravitational field and speeds up (i.e. slides down the potential and has work done on it), this energy is not coming out of nowhere or being used up, its a reshuffling of the energy the smaller mass already had just by virtue of being in the field. The field is an "everlasting energy source" in that you can do that tradeoff between kinetic and potential forever but the total energy won't change (that total energy being zero anyway). Does that make sense?