Physics question

[jeffsg4mac]

Your problem is you have no source of energy. Magnets by themselves can not produce energy.

So if you spun your system to get it going, energy would be quickly absorbed not only in the gearing, but in eddy currents induced in the magnets and released as heat.

So quickly the N/S poles would line up and you motor would stop.

Hmm, Ok I will buy that. If it did go I wonder how quickly the magnets would loose their magnetism? Minutes, hours, days, weeks? And if that is true then why don't the permanent magnets in an electric motor quickly have their poles line up?

 

[highfigh]

Hmm, Ok I will buy that. If it did go I wonder how quickly the magnets would loose their magnetism? Minutes, hours, days, weeks? And if that is true then why don't the permanent magnets in an electric motor quickly have their poles line up?

Most electric motors don't use permanent magnets- usually, only small ones.

 

[jeffsg4mac]

Most electric motors don't use permanent magnets- usually, only small ones.

Yes thats true but size should not matter. The small electric motor magnets don't have their poles line up. Not that I have ever encountered anyway. I mean my slot cars when I was young, the motor on my bait box aerator, electric razors trimmers, various kids toys, speakers, etc. They all last/lasted for years .

Well, sometimes size does matter at least in subwoofers

 

[TLS Guy]

Hmm, Ok I will buy that. If it did go I wonder how quickly the magnets would loose their magnetism? Minutes, hours, days, weeks? And if that is true then why don't the permanent magnets in an electric motor quickly have their poles line up?

Only the armature, the bit that rotates, has the permanent magnet in a high efficiency rare Earth motor. There are field coils to drive the magnet round, powered by the energy source, or from which the power is taken off in a generator.

In an AC motor the sinusoidal wave changes the polarity in the field coil to make the motor turn.

In a DC motor there has to be brushes on a commutator to change the polarity in the filed coil. In the brushless DC motor, there is electronic commutation. In both instances the polarity of the field coils has to constantly change. For powerful motors and generators the filed coil has to be split into three sections, producing a three phase motor. If this is not done vibration destroys the motor or generator.

The magnet will not loose its magnetism. Modern magnets are highly resistant to defluxing.

 

[jeffsg4mac]

The magnet will not loose its magnetism. Modern magnets are highly resistant to defluxing.

That's how I understood it to be. The rest I knew but thanks anyway I once built a DC motor for a HS science class project. I made the damn thing out of nails and wood, and a lantern battery. It worked. I made a speaker that year too. Built the whole thing. magnet, coil, cone. It worked too. Only class I ever got an A in through HS. Rest were all D and F's. ADD thing but they did not know much about that in the 70's 80's.

 

[Stereodude]

As soon as the armature passed the poles of the magnets, current would be induced since it doesn't matter if the magnetic field or the armature that's saturated by the field is moving. That's the principle behind alternators with only one wire- it starts supplying the charging voltage/current as soon as it begins to rotate.

You're talking about coils. He asked about a motor with only permanent magnets. Where's the coil and armature in a motor with only permanent magnets? A motor with only permanent magnets is going to rotate a maximum of 90 degrees once and just sit there. A motor can have no permanent magnets, or it can have permanent magnets on the rotor, or it can have permanent magnets on the stator, but a motor doesn't work without a moving magnetic field. And a motor with only permanent magnets doesn't have a moving magnetic field.

 

[TLS Guy]

You're talking about coils. He asked about a motor with only permanent magnets. Where's the coil and armature in a motor with only permanent magnets? A motor with only permanent magnets is going to rotate a maximum of 90 degrees once and just sit there. A motor can have no permanent magnets, or it can have permanent magnets on the rotor, or it can have permanent magnets on the stator, but a motor doesn't work without a moving magnetic field. And a motor with only permanent magnets doesn't have a moving magnetic field.

The OP was proposing a system of gears to change the polarity of the stator. However that is not going to work for the reasons I outlined.

 

[highfigh]

Yes thats true but size should not matter. The small electric motor magnets don't have their poles line up. Not that I have ever encountered anyway. I mean my slot cars when I was young, the motor on my bait box aerator, electric razors trimmers, various kids toys, speakers, etc. They all last/lasted for years .
Well, sometimes size does matter at least in subwoofers

IIRC, my HO race cars had two magnets and they definitely had to be installed correctly for the car to go anywhere. What do you mean by "The small electric motor magnets don't have their poles line up."? Speakers use fixed magnets and AC signal to move the cone assembly in and out.

The application determines the type of motor and there's a wide range of motors. Synchronous, non-synchronous, AC, DC, etc.

http://en.wikipedia.org/wiki/Brushless_DC_electric_motor

 

[jeffsg4mac]

What do you mean by "The small electric motor magnets don't have their poles line up."? Speakers use fixed magnets and AC signal to move the cone assembly in and out.

I meant that I never had a magnet loose it's magnetism on any electric device I ever owned is all I was trying to say.

 

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[highfigh]

I meant that I never had a magnet loose it's magnetism on any electric device I ever owned is all I was trying to say.

Ahhh. The only things I have that lose their magnetism is bit holders for my drills and that usually happens when I'm in a position where I'll never be able to get the screw back after it falls off and it's the end of a job, with the customer looking on.

 

[astrodon]

motion requires Maxwell's equations

Many have given excellent responses! One needs electromagnetism to produce motion as described by Maxwell's 4 equations of electromagnetism. Magnets by themselves will not produce any type of motion. To quote Scotty from the original Star Trek, you can't change (or was it "break") the laws of physics!

 

[astrodon]

postscript

By the way, before the onslaught of replies to my post that physics is changed all the time -- it is not changed all the time. Physics is continuously modified over time. For instance, special relativity modified Newton's laws of motion, and general relativity modified Newton's law of gravity, they did not replace them. Newton's laws still work very well in their limiting cases, i.e., slow speeds and weak to moderate gravitational fields.

 

[Shock]

Some of the women I saw at the grocery store today surely had their own gravitational pull. I wonder if we could use one of them and put a cheeseburger on a string.....then place them on a treadmill connected to an electric motor.

Perpetual motion done and done.

 

[jeffsg4mac]

Also, it only goes against the laws of physics until someone figures out a way to do it.

 

[highfigh]

Some of the women I saw at the grocery store today surely had their own gravitational pull. I wonder if we could use one of them and put a cheeseburger on a string.....then place them on a treadmill connected to an electric motor.

Perpetual motion done and done.

I see that, too. Usually, they have small children orbiting. Here in Wisconsin, one axe handle is the standard unit of measurement.