# Similarity beetwen magnetic and gravitational field

1. Jul 11, 2008

### atc

Hello everybody!

I was read in a web page that magnetic field act over the ferromagnetic objects in the same way gravitational field act over any material object, mean magnetic field is a potential field energy as gravitational field. (http://van.physics.uiuc.edu/qa/listing.php?id=432")
As you know, a gravitational field of a planet can be used to accelerate a space ship wich passes near by this field and have a certain speed that alow the motion of the ship to be changed by gravitation but also prevent the ship to fall to the planet. This action give an ammount of energy to the ship, increasing its speed.
Now, because magnetic field behave on ferromagnetic materials similar as gravitational field on any material objects, mean is possible to use magnetic field to accelerate ferromagnetic objects, in the same way a gravitational field does with ships?

Last edited by a moderator: Apr 23, 2017
2. Jul 11, 2008

### ZapperZ

Staff Emeritus
Er... you did not understand the analogy. This person answering the question could have easily used an electric field example just equally well. In this case, the gravitational field was used because it is more familiar. But it doesn't mean that such analogy should be implied to mean that they can be identically described (seen any magnetic monopole lately?).

Zz.

Last edited by a moderator: Apr 23, 2017
3. Jul 11, 2008

### atc

OK.
So what's happen then if, let say, a ball bearing having a speed enough high to pas near a magnet placed on a flat table, but not to stick on the magnet?
The magnet will attract the ball and modify its speed and trajectory, isn't it?

4. Jul 12, 2008

### pallidin

Yes, of course, the trajectory of the speeding ball bearing will be modified.

Keep in mind though, that this event also pulls the magnet towards the ball bearing in-flight. Perhaps not much to mention since the magnet is statically attached to what eventually is the earth.

Also, given your scenario, there is a magnetic induction imposed upon the ball bearing as it fly's past a close, static magnet. Thus the ball bearing itself becomes slightly magnetized, affecting the speed and altered trajectory by that virtue as well.

5. Jul 12, 2008

### pallidin

Perhaps this is not relevant here, but I have come across a great deal of misunderstanding regarding magnetic attraction within the general public.

A magnet does NOT exclusively pull towards itself, say, a steel disk. To verify this, one simply needs to have the mass of the steel disk GREATER than that of the magnet, and it will appear as if the massive steel disk is pulling the magnet towards the steel.

In reality, what's happening is that the magnetic field entagles both objects and seeks a collapse to a lesser seperation of the collective center-of-mass. The aspect of inertia provides an illusion as to what is being "attracted", whether it's the magnet or the steel disk. The greater(or static) mass wins the illusion of being "attractive.

Just some thoughts...

6. Jul 13, 2008

### atc

Indeed. Your point is: the magnet act over the ball bearing, changing its trajectory and speed and kinetic energy, but also the ball act over the Earth through magnet, changing its speed, trajectory and so kinetic energy (respecting proportions, of course)?
So, returning to my initial question (can a magnet act similar to a gravitational field, regarding potential energy), this mean, we have an increase of kinetic energy of ball bearing and magnet (or Earth), and the ball continues its trajecory away from the magnet, mean its magnetic potential energy increase (http://van.physics.uiuc.edu/qa/listing.php?id=411"), but also its kinetic energy has been increased. I stil don't understand how this come!

Well, yes, but the question remain the same.

Last edited by a moderator: Apr 23, 2017