Mechanical Rail Accelerator - Non-electromagnet "rail" gun

There's been all sorts of coil guns and rail guns being posted... but here's an interesting alternative. Not really useful, but amusing and effictive as a physics demo. The concept? Conservation of momentum

You'll need some magnets -preferably of the same size, type and somewhat strong (weak magnets do not work as effectivly). You're also going to need some ball bearings that show visible reactions in magnetic fields (aka nickel, coblat and iron/ferrous steel).

You're also going to need a ruler or some sort of straight edge. Movie on next step ;)
Remove these adsRemove these ads by Signing Up

Step 1: Setup and Demonstration

I'm using the magnets found inside the magnetix brand of magnetic toy.

Place one magnet on one ball - then place the ball on your straight edge. Attach to the ball (but not to the magnet), one or two additional balls. You can stop here - or repeat this as many times as you want/can.

Take a different ball - and roll it towards the magnet on the first collection of magnet/balls. You should notice that once the ball is inside the magnetic field, it accelerates towards the magnet and makes contact with the magnet/ball cluster. Once contact is made, the last ball(s) separate in the same direction as the original ball.

This phenomina demonstrates the concept of conservation of momentum. If you were to repeat this demonstration without the magnets, you will have the same results with less motion.

The rest of this instructable has more information/examples for those that want to know more.

Step 2: Giant Clusters - Efficiency

This setup demonstrates what happens when the force of impact is great enough to separate more than one ball.

Setting up:
1st Cluster: Two magnets with four balls
2nd Cluster: Two magnets with five balls

Gently roll the ball into the first cluster. Depending on how much energy you give the first ball (how fast you push it), an additional ball me separate from the first cluster (see second picture). why? The momentum collected just before the initial impact overcame the force required to separate one ball and also the second ball. Ideally, you want all of this momentum going into the first ball rather than the available momentum being split between two different balls.

Going further -- increasing efficiency.

Now, remove one ball from the first cluster. But leave the second cluster alone. (See third picture) Repeat the experiment.

Notice in the fourth picture (after impact), that the first cluster remained intact but the second cluster is missing two balls! why? Because more momentum was put into the ball ejected off the first cluster (simply by removing one ball from the system), the momentum going into the second cluster was great enough to remove two balls.

why do the balls stick together in the first place? In case someone needs to ask. This is due to the magnetic force between the balls and magnet. Even the final ball has a magnetic force on it, but that force is weaker compared to each ball closer to the magnet. To proove this - make the first cluster made up of one ball. Now, gently push another ball into it. The ball/magnet system will not separate because the force between the magnet and ball is too great.

Step 3: Ramps!

What happens when we go up a ramp?

To demonstrate a special case, I setup this demo to show what happens at a sort of "critical point."

From the first image, you can see that the second cluster is quite large -- and there are balls on either side of the magnet. We will gently push a ball into the first cluster and see what happens.

In the middle of the action (picture 2). Notice how the last ball in cluster two is blurry -- it is currently in motion - going up the ramp.

Aftermath (picture 3). What happened? It looks like we ended just where we started?

Why? As the ball on the end of cluster 2 goes up the ramp, it is gaining potential energy as a result of gaining height. Once it reaches its apex, it will return down the ramp and impact with cluster 2. The imparted momentum is great enough to release the ball on the opposite end of the cluster resulting in picture 3.
Crash21087 years ago
Could this be turned into some sort of perpetual motion machine? Doubtful seeing depressing new-age thermodynamic laws. What changes would need to be implemented to keep this going in a loop?
Perpetual motion does not exist. Imagine a long track of the magnets/ball bearings arranged in a circular pattern. Consider an unfired pair of bearings as the ground state, then fire and you will see that the ground states activated by the processs of firing cannot fall back on their own to their original ground state where the loop is tied up. Undo this by adding more bearings? You might get lucky and have the thing run a few loops (might = no chance). You will always end up having an activated state (taken up energy, none to release), that has to give energy to activate something which is already in its activated state and that cannot fall back without energy input. Dead end. Just began typing this response, then scrolled down to see the rest... Sorry, could go on at length with the answer... The only (almost) perpetual machines around are atoms, but then again, they are not machines: their electrons keep spinning (rather, existing) around the nucleus for (an estimated) 1x10^30 years. That's (almost) perpetual (and useful) because it keeps my body intact and prevents me from becoming a black hole, which reminds me of a very nice Gary Larson cartoon...
Perpetual motion does exist, just not in any state achievable on earth. The formula should go something like... momentum+resistance >= gravity+friction
Attmos Dr KAZ2 years ago
what about the earth around the sun, or the moon around the earth? perpetual motion?
trebuchet03 (author)  Attmos2 years ago
Newton's Laws of motion explain fairly well... Earth is sufficiently far away and of significant mass that small forces are nearly insignificant on Earth'y orbit. Comets, however, make up for a lack of mass with velocity which is why they can have open orbits and escape the sun.

The moon, on the other hand, is slowly being pushed away from Earth. About 4cm per year resulting in Earth's rotation slowing about 2 seconds every 100,000 years due to tidal forces and tidal locking (same reason we only see one side of the moon).

Satellites experience significant orbital decay as their mass is much smaller compared to Earth's mass and their distance is EXTREMELY close. Small forces due to atmospheric particles have large consequences over time.

The Earth, Sun and Moon are in motion, but their motion is not perpetual.
we're way off topic about your rail gun, which is a cool display of physics by the way, and i'm sorry for this, lol. I get and agree with the moon thing, I'm not so conviced about the earth around the sun. newtons first law says, well you know what it says. there is no fluctuation or transfer of energy, just a perfect balance between gravity and centripetal force. is that not perpetual? lol, i'm really sorry, these things just eat at me until i get an answer i can understand. what do you think?
trebuchet03 (author)  Attmos2 years ago
Balanced forces does not necessarily mean perpetual. They just mean forces are balanced.

The Earth happens to be travelling through a vacuum - there really isn't much that will slow it down but things do. Meteorite strikes, technically, are forces on Earth. Earth has several orders of magnitude more mass - this is like throwing a grain of sand at a cannon ball. Sure, the grain of sand applies a force, but it's imperceptible.   Other than meteors, nearby asteroids and other celestial bodies will exert nonzero gravitational forces - Earth is still much larger - so large that it's irrelevant here...

To note: Earth is slowly moving away from the Sun - about 15cm per year. Slowly, we're stealing angular momentum from the Sun so that we may move into a higher orbit. On a human scale, this orbit is forever and perpetual. For the rate at which this occurs, the Earth will be swallowed by the Sun long before there's any orbit issue.
cool. well thanks for indulging me. it's fun for me to learn about stuff like this and to be able to ask a few questions. the science channel doesn't do a good job of answering when i talk to it, lol.
also if you had a "prepetual waterwheel machine" it would stop because of friction from the wheel turning
smb64 Dr KAZ2 years ago
 not unless you use a portals gun and have the track on a ramp.  : )
arent perpetual motion machines... erm... impossible??
Pure perpetual motion machines .. . are, unless in a perfect universe, which .. we are not in :P. Near perpetual motion machines on the otherhand are quite possible. :P, Meaning they go for a REALLY long time, but technically, not forever ;P.
chloride ARVash6 years ago
yea because some of the energy is given of as heat upon collision
Just don't have it collide. Suspend whatever machine with magnets instead of ball bearings and have it in a vacuum.
bujo0 Crash21086 years ago
still will lose energy to fiction from the balls on the track, and its very difficult to get a perfect vacum on earth, unless you mounds of money.
lbrewer42 bujo03 years ago
Not really - many politicians achieve this state between their ears ;))
ARVash bujo06 years ago
right, and then the only perfect vacuum on earth will be your wallet.
_soapy_ ARVash6 years ago
You will also lose energy to the magnetic material - the magnetic material uses a tiny amount of energy to flip it's magnetic domains about, every time the magnetic field reverses. This adds up with a lot of time. Also, you will get effects like friction in the string or track which will kill the motion fairly quickly, even in a vacuum.
friction from the track would kill everything
trebuchet03 (author)  Crash21087 years ago
ahh this question... the quick answer is no. Every time the ball impacts, you loose some energy. Not to mention, the setup in this is vital - you want balls making contact with magnets, not with other balls. So eventually, the whole thing fizzles out - even in a straight line (assuming all magnets are about equal). Check out the link that crawler posted - that person explains it with a bit more detail. For testing how much energy is lost on impact, they suggest putting a ball in a tube -- then dropping another ball on top from a measured distance. If say you drop from 6 inches and it only bounces back up 2 inches that is a 66.6% loss of energy.
actually they aren't losing energy. the magnets are adding energy at each stage. the real reason you couldnt use it as a perpetual motion machine is that after the first trip around there is no ball to continue post impact. (assuming use of 2 ball and one magnet at each stage) if the ball isn't there to go onward the magnet absorbs the shock and transfers it to the ruler and stops the chain.
trebuchet03 (author)  finfan77 years ago
while that is true - someone could argue an infinite amount of balls. If that were possible, the reaction would stop due to energy losses before getting to the nth ball -- the same goes for a huge amount of balls. ANYTIME you have a collision, it is not elastic as there is no such thing as a perfectly rigid material, this inefficiency is released as heat. For the sake of simplicity, many collisions can be considered elastic - such as pool balls. But in the case of perpetual motion, small bits add up over time which is the fundamental downfall of any perpetual motion device...
Must be that "depressing, new-age" Second Law of Thermodynamics. "There is no process that, operating in a cycle, produces no other effect than the subtraction of a positive amount of heat from a reservoir and the production of an equal amount of work." So basically like Trebuchet said; as each of those collisions produces heat, a fractional percentage of the mechanical energy that produced it is lost as radiant energy being emitted out of the system. Entropy sucks...stupid hippies. :p
there where 2 people that DID build a prepetual motion machine, and it DID give more energy out than was put in. one guy built it with magnets, one guy build it with hydraulics. I'll get those papers out someday and post them for u guys. scientists arent always right.
So why is the world still relying on oil for energy and not building these perpetual motion machines? Perpetual motion could only happen in space, balaced evenly between all magnetic fields, where there's no air to cause resistance and loss of energy.
What do you say about that, James?
Theres too much money involved in the oil business right now. if that where to shut down, the worlds economy would crash. if you read stuff about people that built these machines, every one of them was told to stop by the government. Did you ever think that scientists just MIGHT be wrong when they say that its impossible? did you know that it used to be tought in schools, and was confirmed by SCIENTISTS that the earth was flat?
Erm... "Scientists" have known the earth was round for pretty much as long as there have been scientists. The ancient Greeks knew it! What you are thinking of is the "Dark Ages" when science was told what to say by religious men with swords. There is no conspiracy, though. f it were possible, someone would have stuck it on Instructables by now, since they would already have sold enough electric back to the local grid to retire wealthy.
Do you realize how much money the oil companies are making, and that they don't want to lose that?
I pay £600 a month in diesel for my van. Fuel in the UK is near $8.50 US for a US gallon. It's scary. I'm currently looking at ways to enhance the fuel efficiency of cars and vans with some of the hydrogen kits that are on the market. Once I'm happy they aren't fake. If I can work out a good way to make 50p a year worth of electric to sell back to the grid, I'll do it. If you can show me a way to generate energy from magnets (or anything) that requires less energy in, I'll pay the start-up costs, and give you 90% of the profits and a 49% share. There is not a thing "big oil" could do about it. Major governments cannot stop important things like press reports of royals being on the front line, or rape videos getting on YouTube, so how could they suppress so perfectly an idea for something people actually desperately want?
I dunno. theres no money in stopping those videos though, so that could be it. people are crazy about money, and it ticks me off.
So why wouldn't you just keep using it and sell energy to neighbors? And to stop needing oil from other countries would b better for the U.S., at least, unless you're not from here.
I dunno. I don't know if your being argumentative or just curious or something but I have lost all desire to argue with anybody about anything. if you did all that you described eventually word would get out and they would shut it down. thats my opinion and I wont force it on anybody.
Okay, James.
but if you weren't being argumentative, then I'll gladly explain it.
I refuse to believe that perpetual motion machines are being buried under some conspiracy lobby. Its just so convenient for the snake-oil salesmen and those really wanting to believe that everything is some big cover up by the man. Oil companies are greedy, but the nature of this knowledge would have led some of those countries that are really forward in a protectionist kind of way (Iceland and Sweden) to go ahead and adopt them and become independent right away. Those links to the papers are conspicuously absent. Please dig around and post them. I really want to read them to see if my gut response is right.
ok. I'll have to talk to my neighbor about the hydraulic one by his father in law; and I'll post get the ones for the magnetic one out and scan them in.
That'd be great. Thanks.

One of my idols is Richard Feynman, the physics author. Here's a link to a blurb he wrote about perpetual motion machines if you are interested.
thats not a perpetual motion machine, thats one that runs on really effecient fuel. well....they claimed it did at least.

Get More Out of Instructables

Already have an Account?


PDF Downloads
As a Pro member, you will gain access to download any Instructable in the PDF format. You also have the ability to customize your PDF download.

Upgrade to Pro today!