Gauss Gun

A Quick Gauss Gun Post

In a simple Gauss Gun a steel ball rolls toward a magnet with two balls on the opposite side of it.

The ball nears the magnet, which pulls on the ball and increases its speed.

The ball slams into the magnet, which transfers the energy and momentum of the ball to the first ball on the other side. The first ball transfers this energy and momentum to the second ball-which goes shooting off.

The last ball shoots off at a much faster speed than the original ball because of the increased acceleration provided by the magnet as it "grabbed" the original ball when they got close to each other.

The magnet with two balls on one side is a stage. You can set up many, many stages in a row to create a chain reaction with a pretty fast moving ball shooting out of the last stage.

Rolling friction, aerodynamics and the magnets pulling too hard on the secondary balls can steal some of the energy and momentum by not letting the last ball go easily to the next stage. A way to counteract that is to use electromagnets (coils) that shut off right as the stage receives the incoming ball.

I came up with an easier solution: have the first of the two balls be non-magnetic! It acts as an isolator between the magnet and the second ball that gets launched to the next stage.


Another thing that steals energy and momentum is if the magnet slides backwards a little to meet the incoming ball a little earlier. The solution: I taped the magnets down so they wouldn't move.

Experimenting with different sized ball bearings, different numbers of them and different strength magnets all have noticeable effects on performance. As do the spacing between stages.




Here's some simple performance test videos I made:

I found that K&J Magnets has some medium sized magnets and balls that work even better than larger ones. I had great results with the quarter inch (D44) ones:

K&J also have an awesome blog with tons of projects like this (which include links to their industrial products if used in the experiment). Very cool! 

K&J also explain the science behind Gauss guns (and magnets in general) without delving needlessly deep into Newton's Second Law of Motion, as most explanations online do. Hint if you read up elsewhere: a euclidean vector is just an annoyingly complex way of denoting an arrow. "The ball shoots that way!"

If you're interested, F=MA , Force equals Mass times Acceleration. You have to kick heavier balls harder to get them to go the same distance. What's important is that Acceleration here is just the initial jolt/kick, just like the better quick on/off electro-magnets in a coilgun! It sets the object in motion. That is all (and that is the best part). Newton's Third Law of Motion is the equal and opposite reaction one: which is why taping the magnets down is better: no jolting back and forth. The tape helps conserve energy.

Newton's First Law is just the one about inertia: objects at rest or in motion stay that way unless acted upon by unbalanced force. It's why the balls eventually stop instead of blasting a hole in the universe.

If you add a bunch of stages you might just get some cool results, but you might shatter a magnet or put a hole in something! Eyewear is a must! All the laws take their toll on the Gauss gun, especially a simple one like this.

However, at some point I'm going to try 20 stages firing .177 pellet gun bbs. I have a feeling their reduced mass (M) will insurmountably hinder optimal performance.

Carl Friedrich Gauss worked on a lot of number theory mathematics, but he also founded the "Magnetic Club" in 1883. He has a unit of measure (the gauss) named after him. It measures magnetic fields, and Gauss formulated ways to measure the properties of magnets using only the simple concepts of time, mass and length. Specifically, he came up with a better way of measuring the oscillation of a magnetized needle to measure magnetic field intensity. This used to be measured in a unit called the gauss, but they changed (in 1932) the term gauss to refer to electromagnetic induction, and field intensity was then notated in units called oersteds--Hans Christian Oersted discovered electromagnetism in 1820.

Magnets actually have different gauss values for their different fields (surface, residual flux) and all things being equal a physically larger magnet will have a lower surface field! So, magnets have various other ways of denoting their "strength". The easiest is pull force: how many pounds can it lift or pull?

Another is the N number, which is derived from a magnet's MGOe (Mega Gauss Oersted) value. Neodymium rare earth magnets range from N35 to N52. This is the amount of stored energy (energy density) in the magnet.

Speaking of energy, check out what else these magnets can do:

The magnets used in this post were all N42 magnets. The white part of the gun was just a piece of ceiling molding. Just scraps.

I need to borrow the Gauss gun just one more time, Meow!