# Magnet passing through a copper pipe

Discussion in 'General Electronics Discussion' started by Dretron, Mar 2, 2013.

1. ### Dretron

101
0
Jun 9, 2012
Hi

An electromagnet applied a repulsion force on a magnet that shot the manget throughout a copper pipe.

The total force applied to move the magnet is 200N.
The initial velocity of the manget is 100 m/s, as it passes through the copper pipe we know that it would decrease speed due to eddy current the oppose the magnet.However, what would happen if the force that caused that velocity, that is moving the magnet is constant at 200N?

Would the magnet still have that speed? Or would it slightly decrease? Or significantly decrease?

I guessed the terminal velocity would be less, but just by a few.

I know this depends on a lot of aside from what I've stated, but, just by guessing what do you think will happen?

2. ### duke37

5,364
772
Jan 9, 2011
Only a guess.

The opposing force will go up as the speed goes up, therefore there will be a balance at a certain speed when the drag equals 200N. This may be above or below 100m/s.

3. ### Dretron

101
0
Jun 9, 2012
How can it be above?
And how can it be below?
Granted that the copper pipe is of short distance btw.

4. ### duke37

5,364
772
Jan 9, 2011
Suppose you have an infinite pipe.
Suppose that the drag is 1N/(m/s).
Then with 200N push, the speed will settle at 200m/s.

If the pipe is short, the speed will not attain balance.

5. ### Dretron

101
0
Jun 9, 2012
No, the drag is 200N
Exactly the same as the applied force.
I think the terminal velocity will reach to zero.

6. ### Dretron

101
0
Jun 9, 2012
I think the opposing force is constant as the magnet is going through the pipe.
Just like the applied force as well.

So I'm not sure what would happen.
But I assume it would stop.

Why would it balance though?

7. ### duke37

5,364
772
Jan 9, 2011
You said that the drag was due to eddy current losses. The drag will approach zero as speed approaches zero. So the oposing force is not constant.

If there is a 200N applied force and 200N drag, then the speed will not change. Why should the magnet stop?

8. ### BobK

7,682
1,688
Jan 5, 2010
Where is the opposing force coming from when the magnet stops moving?

Bob

9. ### Dretron

101
0
Jun 9, 2012
Sorry,
The opposing force is not constant nor is the applied force honestly.
As the applied force is applied with 200N and distance is 0, as the distance increases the force decrease(200N), thus the resistive force from the eddy current with start at a certain force and drop gradually as well since the speed is also decreasing and the main applied force too.

No where.
The opposing force really comes from the induced currents.
So if the magnet speed is 0, the opp. force is = 0.

Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Continue to site