# A question regarding an experiment with a magnet and a tube

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1. Apr 30, 2015

### Thomas_phys

1. So, during one of my classes, the teacher showed us a small experiment, and asked us to explain how it works. The experimented consisted of a tube, closed on both ends, and attached to said tube is what I think is a magnet. Now, everytime he rotated the tube, the magnet rised to the top with a constant velocity. I held the tube and it felt as if there was a liquid moving inside the tube whilst rotating the tube. Extra: I'm pretty sure the tube was PVC.

3. As I felt a movement, I thought the tube would be filled with a heavy liquid, pushing a magnet on the inside of the tube to the top of the tube when you rotate it, so the liquid must have a higher mass density then the magnet, but this was not it. Any help?

Sorry for my english, not my native language..

Last edited by a moderator: Apr 30, 2015
2. Apr 30, 2015

### Thomas_phys

And as the magnet on the inside is pushed up, and is "connected" with the magnet on the outside, he takes the magnet on the outside with him.

3. Apr 30, 2015

### Staff: Mentor

Were you able to see inside of the tube? Or are you saying that you couldn't see inside of the tube, but there was a magnet outside of the tube that moved up to the top end of the tube when you flipped it over? Can you post a sketch?

4. Apr 30, 2015

### Thomas_phys

Hey!

First of all, thank you for answering!
Second of all; no, I was not able to see the inside. Do you have any idea for a program I can use to send a sketch?

Again, thanks a lot for helping me out here! :)

5. Apr 30, 2015

### Staff: Mentor

You could do a hand sketch and scan it at a copier to make a PDF file that you could upload. You could also take a photo of your sketch and upload that, but often cell phone photos do not turn out so well in the forums.

Was there a magnet outside of the tube, and that is what was moving that you could see?

6. Apr 30, 2015

### Thomas_phys

Yes, There was a magnet outside of the tube. The magnet moved up in a straight line, thus it went against the gravitational force. The tube was around 50 cm/ 20 inch long, with a circumference of around 5 cm/ 2 inch .

Also noteworthy: the speed was constant, so no acceleration at all, even in the beginning.

Thanks !

7. Apr 30, 2015

### Staff: Mentor

Okay, that makes more sense. And you are asked to figure out what is going on, correct?

So your initial guess is pretty close. There must be a magnet (or something that attracts a magnet) inside the tube. I also think you are correct that the liquid in the tube is not denser than the object inside the tube. So what else in addition to liquid and metal could be inside the tube that would cause the metal object inside to rise to the top of the liquid?

8. Apr 30, 2015

### Thomas_phys

Any hints? I haven't found a thing that could be it... Sorry .. :/

9. Apr 30, 2015

### Staff: Mentor

I gave you some big hints in my previous post.

10. Apr 30, 2015

### Thomas_phys

I thought about a second magnet, that pushed the other away, but that makes no sense.
Secondly, I thought about some kind of bubble mechanic, but that sounds impossible.

So, it may be obvious, but I can't see it :(...

11. Apr 30, 2015

### Staff: Mentor

Don't say "can't" -- stay positive!

You are on the right track when you say "bubble"... Keep going down that path...

12. Apr 30, 2015

### Thomas_phys

Alright :D Sorry, I had the feeling I was getting on your nerves there.

I'm thinking out loud here: To get that "bubble" mechanic, I will need a rather "dense" liquid, maybe honey or something.
I will probably encounter a problem; there is no force that will pull said bubble up, gravitation will rather pull it down. Another obvious problem is that most bubbles are quite unstable, so I'll need to find a liquid that can "hold" a bubble.

As most bubbles break when they touch a surface, the tube must be filled to the brim with the liquid. As I could hold the tube, it won't be a super-heavy liquid.
(As my physics teacher expects us to create one at our homes, it won't be expensive/illegal/hard to get, so it's probably a household product)

So, I'll need a liquid that can hold bubbles and I, as a 18 year old, can get my hands on. But more problematically, I need to find a solution to the aforementioned problem with the gravitational force.

I'll be back in an hour with what I think might be it, just going to search some things up on the internet. So if there are any grave mistakes, please correct me ! :)

And really, thanks for the help! You're doing me a tremendous favour right here.

13. Apr 30, 2015

### Staff: Mentor

Hey, you're doing the work, not me.

I think you can just stick with water for the liquid, that's what I would use if I were building this. And as for the bubble, what happens when you hold a pin-pong ball under water and release it? What does it do? And if you put a ping-pong ball in a tube of water where it is just a little loose (diameter of the ball is slightly less than the inner diameter of the tube), and turn the tube over, what does the ball do?

14. Apr 30, 2015

### Thomas_phys

Aha! Thanks!!!!!
So I need to find an object that behaves like the ping-pong ball as you said, but not only that, but it's also gotta be magnetic. I wonder where I'll be able to buy that :)
I'll go and think about that, thanks again !!!!!!