# Basic Straight Line Permanent Magnet Accelerator

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• MarcusThatsMe
In summary, the video on YouTube features a horizontal permanent magnet accelerator with a spherical magnet that appears to increase in velocity while traveling from left to right. There are questions about the role of the larger magnets at the end and whether the smaller magnets are necessary for achieving the end velocity. It is also discussed if a long line of smaller magnets could continuously increase the velocity of the spherical ball. It is noted that railguns do not use permanent magnets and instead use a high current through rails and a projectile. The closest equivalent would be a coilgun. The conversation also touches on the efficiency of replicating the experiment with permanent magnets.f

#### MarcusThatsMe

TL;DR Summary
Horizontal Permanent Magnet Accelerator Question
I stumbled upon this video on YouTube:

Here is a screenshot with some colored lines added of the part that generated a few questions in my head that I hope some of you smart folk can answer for me.

In the video, the spherical magnet (at the end near the two big magnets) appears to increase in velocity while traveling from left to right, with that in mind my question is:

Is the increase in velocity ONLY due to the larger magnets at the end?

If Yes...

a) Does that mean you could technically remove a number of those smaller magnets (red line)?
b) Do you even need the smaller magnets (red line) to achieve the end velocity, would you really just need a line of middle size magnets (purple line) before the last size (green line)?

If No...

c) Could you technically just create a LONG line of those smaller magnets (red line) and have the spherical ball continuously increase in velocity if going in a straight horizontal line?

Last question...

I know that as the spherical ball passes each set of magnets it has to enter and leave those magnetic fields (which is why I believe railguns use magnets you can turn on and off so you don't have to deal with leaving the field, you just make it disappear as the next field turns on, but I want to focus on permanent magnets), would it be more useful to place them closer together or to ditch the circular magnets for rectangle or square magnets.

My kids liked the video, so we were thinking of replicating it while trying to increase the velocity, however, it would be great to replicate in a more efficient manner if there is one utilizing permanent magnets.

Neglecting differences in friction you could remove everything apart from the last few magnets and release the ball closer to them.
c) Could you technically just create a LONG line of those smaller magnets (red line) and have the spherical ball continuously increase in velocity if going in a straight horizontal line?
No. This is directly clear from conservation of energy.

Railguns don't use permanent magnets at all, they use a high current going through the rails and the projectile (or a sled carrying that projectile). The closest equivalent would be a coilgun which - as the name suggests - uses coils that can be turned on and off to keep accelerating the projectile.

russ_watters
Neglecting differences in friction you could remove everything apart from the last few magnets and release the ball closer to them.
That's what I was thinking.

This is directly clear from conservation of energy.
That's logical.

Railguns don't use permanent magnets at all, they use a high current going through the rails and the projectile (or a sled carrying that projectile). The closest equivalent would be a coilgun which - as the name suggests - uses coils that can be turned on and off to keep accelerating the projectile.
That was sort of my limited understand. Each coil would activate to pull the projectile then the previous coil would deactivate to release the magnetic hold and the next would activate to accelerate/pull it ahead until eventually its just released from the final coil at a high velocity.