# Homework Help: Magnetic train

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1. Dec 19, 2015

### 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)

Last edited by a moderator: Dec 20, 2015
2. Dec 19, 2015

### Staff: Mentor

How do you mean that question?
A force can change velocity.
Descriptions of the train concepts discuss that.

3. Dec 20, 2015

### 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?

4. Dec 20, 2015

### 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.

5. Dec 20, 2015

### 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.

6. Dec 20, 2015

### Staff: Mentor

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.

7. Dec 20, 2015

### 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.

8. Dec 20, 2015

### Fightfish

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

9. Dec 20, 2015

### mathewmical

yes that´s right

10. Dec 20, 2015

### Fightfish

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

11. Dec 20, 2015

### 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.?

12. Dec 20, 2015

### Staff: Mentor

It does not, and there is no need to. The train is supported from below by the coil.
It is useful to analyze horizontal and vertical forces separately.

13. Dec 20, 2015

### mathewmical

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

14. Dec 20, 2015

### Staff: Mentor

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.

15. Dec 20, 2015

### mathewmical

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

16. Dec 20, 2015

### Staff: Mentor

Right.

17. Dec 20, 2015

### CWatters

How a maglev train works..

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

Last edited by a moderator: May 7, 2017
18. Dec 20, 2015

### Staff: Mentor

This is not the type of train discussed here.

Last edited by a moderator: May 7, 2017
19. Dec 20, 2015

### 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

20. Dec 20, 2015

### mathewmical

okay i´ll do so :D

21. Dec 20, 2015

### mathewmical

22. Dec 20, 2015

### Staff: Mentor

I added it to the first post.

23. Dec 20, 2015

### mathewmical

thanks a lot

24. Dec 20, 2015

### 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 theres four times FR so theres 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?

25. Dec 20, 2015

### Staff: Mentor

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