Investigating Magnetic Train Forces: A Puzzling Inquiry

[mathewmical]

Hello
I hope you know the phenomenon called "Magnetic train". My teacher used it in classes to demontrate electromagnetic phenomena. So he told the advanced learners (however, here I am xD) to investigate it, especially the forces and how certain parameters affect the velocity. But I do not understand at all how there can be a velocity with a force? and which forces appear? I hope you can give me at least a thought-provoking impulse.

thanks a lot

Ray

Image added by mfb to clarify which type of train is meant (see page 2)

 

[mfb]

But I do not understand at all how there can be a velocity with a force?

How do you mean that question?
A force can change velocity.

and which forces appear?

Descriptions of the train concepts discuss that.

 

[mathewmical]

yes but there seems to be a constant velocity and i wonder how this can be. woundn´t it be changing all the time?

 

[Flower_648]

Due to inertia, something with no net force will maintain a constant velocity. A magnent suspending a train can precisely counteract the force of gravity, allowing the train to move at a constant velocity because the sum of forces is zero (they act in opposite directions). I think you might be asking something deeper than that, though, I'm not sure.

 

[mathewmical]

very interesting, thank you! i agree but how does a magnet counteract the force of gravity when they are perpendicular to each other?

i think there is only the force of attraction and the force of repelling. and the force caused by friction that opposes these two other forces. And gravity.

 

[NascentOxygen]

It may be called a "magnetic train" but the magnets are not used to attach each carriage to the next one; the main function of the magnetic field is to raise the train off the tracks...to give a small clearance. [emoji52]

 

[mathewmical]

that´s not what i meant, my experiment refers to a battery in a solenoid where there are magnets attached on each side of the battery. if you put it into, it´ll start to move.

 

[Fightfish]

I think the OP is referring to this particular experimental demonstration, where the "train" is a battery with magnets attached to its ends, traveling through a wound copper wire "track".

 

[mathewmical]

yes that´s right

 

[Fightfish]

yes but there seems to be a constant velocity and i wonder how this can be. woundn´t it be changing all the time?

My instinct would be that this is due to the back-emf that arises from electromagnetic induction effects...though I'm not that sure...imhomogenous magnetic fields are always tricky to analyse

 

[mathewmical]

so it is possible that it gains speed due to the back-EMF and than move till the battery is empty because of the forces.?

 

[mfb]

very interesting, thank you! i agree but how does a magnet counteract the force of gravity when they are perpendicular to each other?

It does not, and there is no need to. The train is supported from below by the coil.

i think there is only the force of attraction and the force of repelling. and the force caused by friction that opposes these two other forces. And gravity.

It is useful to analyze horizontal and vertical forces separately.

 

[mathewmical]

hmm i just thought there are only horizontal forces because of the friction

 

[mfb]

Well, there is certainly a vertical force from gravity, and something balancing it (so the train doesn't fall through the table). Otherwise the train would float, and there would be no (horizontal) friction either.

 

[mathewmical]

of course, but theforce from gravity is only important for the friction and the normal force neutralize it. right?

 

[mfb]

Right.

 

[CWatters]

How a maglev train works..

https://www.quora.com/How-magnetic-levitation-train-works

 

[mfb]

How a maglev train works..

https://www.quora.com/How-magnetic-levitation-train-works

This is not the type of train discussed here.

 

[Fightfish]

mathewmical, I think you should edit your first post to include a picture of that particular experimental demonstration you're referring to, because "magnetic train" immediately causes most people to think about maglev trains =p

 

[mathewmical]

okay i´ll do so :D

 

[mathewmical]

isn´t working. so i´ll post it here:

http://www.waynesthisandthat.com/images/HT 994.jpg

 

[mfb]

I added it to the first post.

 

[mathewmical]

thanks a lot

 

[mathewmical]

okay i just got another idea: if i only focus on, like, 3, single loops. if the battery touchs two of them, the current flows and the like pols repel each other with FR, so on the battery there will be twice the force because of Newtons third law. the same with the unlike poles . so all in all there's four times FR so there's an acceleration. then, due to inertia it moves on to the next loop and then it starts again? then its resonable to have an apparently constant velocity. what do you think about it?

 

[mfb]

If FR refers to friction: why do you expect fixed relations between magnetic forces and friction?

 

[mathewmical]

FR refers to the force one magnet exerts on the other one (R due to 'repelling'). maybe if i manage to calculate the force I can figure out the acceleration between two loops.

 

[mathewmical]

or wait could it be that first there's an acceleration, but due to the voltage induced by the fixed magnets the voltage of the battery will be compensated so it will remain with a constant velocity?

 

[Carson Birth]

http://physics.stackexchange.com/questions/150033/how-does-this-simple-electric-train-work

This explains it really nice.

 

[mathewmical]

That´s all? then is there a way to calculate the velocity?

 

[mfb]

Not with reasonable effort.
You can make rough estimates if you know friction and some coil properties, but it's not like a typical homework problem where you plug in 3 numbers in a formula and you are done.