Professor Eric Laithwaite: Magnetic River 1975

Permanent magnets are difficult things to understand, in fact, if we are absolutely honest with ourselves, we don't understand them. You will see that either end of a bar magnet will attract a piece of steel, but that doesn't follow because it is painted ready to magnetize. because the wood won't pick up that piece of steel but this one will, so this is the magnet, but the only real test between two magnets is whether, in addition to attracting each other, they will also repel each other when the idea of ​​repulsion is now reversed. you get the impression that maybe you could float one of the magnets over the other so now i can feel the repulsion now look what happens when i let go ah you see he won't stay there you get repulsive force but we say it's not stable now people have proposed this idea of ​​suspending railroad cars over the track because it doesn't use energy, but then you have to do something to stop it from falling sideways now we can make

magnetic

rings like these, in this case, an entire side is one The North Pole and all the other one is a South, so if we get two of them, we can try to float one over the other and again you will see that you get lift, but we can't achieve stability unless we put a glass tube. and you float or not, it's just wonderful.

It is suggested to people that you could use this for floating railway cars, but you see that the clearance there might not be big enough, so what we would really like to have are some more magnets to make it stronger. going more or less in the right direction, now we're getting a lot of clearance, but of course these magnets would be on the track and this would be the vehicle, so it's going to be very expensive, you want hundreds of miles of this, so , what are we going to do? What I would really like to do is put a single magnet on the track and add more magnets on the vehicle.

Two magnets. Three magnets. The gap instead of getting bigger is now getting smaller, so this is a situation that gets worse as it gets bigger. not good for railway vehicles now there is another type of magnet that does not involve the use of rings or anything like that, instead of a coil of wire we will take an iron bar and push it through the center of the coil and then it passes an electrical current through the coil, this meter will tell you how much current passes, you would connect that very. I'll connect it, how do you connect the switch, now all we need is a battery to connect here and we should You will be able to make a magnet with that steel bar that, by God, is not magnetized.

If you give me the chart, Donny, we can see if it really behaves like a magnet, because there is a magnet here right now. This is just an iron barn, so the magnet will attract either end. Now let's see if we can make it reject by turning on a current. That end will now attract and that end will repel. Now we have made an electromagnet, but will it work without it? the iron core we just use the coil, but it certainly attracts and we turn it and it just repels it, so it's still a magnet even though it has no iron at all, but of course if we put the iron core back in, then The attraction and repulsion are much greater, so we make a better magnet.

Now let's see how much weight we can lift with this magnet, approximately on the iron bar. I'll see if I can lift this heavy iron bar and we can just, it's not really jumping. to find it, but after I have made contact I can simply lift it, but there is more magic in an electromagnet if instead of powering it with a battery we power it with alternating current. Look at this oscilloscope, you see a point that goes up and down. That point is actually measuring the amount of current that flows in a wire when it is above the midline, the current flows in one direction and when it is below it it flows in another.

Now I slowed down to show you what's really happening, but in your house you have an electricity supply that goes up and down much faster even faster than that goes up and down 50 times a second now let's take a look at a electromagnet that uses that type of supply and this is a coil of wire with a long iron core It is an aluminum ring. Aluminum, you know, is a non-

magnetic

substance. We cannot lift it with a magnetic bar, as can be done, for example, with a bunch of keys. So we have this non-magnetic ring over this iron core and the switch.

There you see that the ring is thrown very high into the air if I put it back on without turning it off and it floats but notice that it never floats level and in the center it always has to rest on the pillar just like the permanent magnets did if I put a ring thinner does not float as high ending up even lower and if we go to the last and cut a ring of kitchen paper it is also aluminum that does not float at all, but unlike our permanent magnets if we now add a few more rings we will start to see everything the lifting remember with the permanent magnets the more magnets we put on the top and the smaller the lifting and in this case the more rings, the higher the lifting, put the thicker one on even thicker and go up, it reaches directly to the top now what is the secret of this amazing device this is the gift this is a copper cylinder that can rotate freely if I hold the copper cylinder next to it not much happens but if I take this ring that wants to float up there and I force it up down next to the copper, then the copper starts to spin and if I put it on the other side it spins in the other direction, it's like there is something that moves up and makes the copper spin. and we call that sweeping something, a traveling magnetic field.

Now this is a row of electromagnets deliberately arranged to produce one of these traveling magnetic fields, so when I turn it on put our copper cylinder over it and there you see the same effect as if something was sweeping underneath let me put some aluminum on it, it push, but not too fast, let's try a bigger piece, which is better, even bigger, better, still, you see, the bigger you are and the better it will be, this, of course, we call it a linear motor now suppose we increase the current, would you mind increasing the current Barry?

Now we can hold a sheet of aluminum that is not only trying to be pushed but also raised above the surface; is much more like what I would expect if I threw a piece of wood into a flowing

river

, it would float and move, so this is the beginning of a magnetic

river

, but it has no banks, because you're right, take my phone away from me and it will appear the sign. If I carry it too far towards you from the other side, but if we could just stabilize it, then we should have something that looks exactly like a river.

Now how does all this work? Could you say that you are right? This is a mechanical model of what You just saw that instead of a row of coils we have a row of locks, we will power them with alternating current so that each one can go up and down and when we turn everything we have the impression of something. traveling, but I want you to realize that nothing actually travels because each rod only moves up and down. What makes it real is when we put something in one of the valleys of the wave, then something real travels connecting with the other work.

If you look at a single rod like this you will see that it just goes up and down, there is no horizontal movement, just the ball is real and moves from side to side. It is exactly the same with this magnetic river. I can change. It's on and there's nothing on top, nothing moves on the TV until I put the aluminum and the light on, put the ball on the rod, so this is our first step towards a magnetic river. This is a single coil and a single sheet of aluminum. it's going to behave more like our jump ring, it turns on and tries to put it back on, it floats, it has a really good try and it floats but it doesn't make it, but if we don't put it in the middle of the coil, say it like that. and it doesn't jump up that width on this side.

I put it towards the link, so let's use this rotating cylinder again to see what's going on. Turn on, place the cylinder in the center. No problem. Insert the plate and turn. Enter the plant on the other side turns the other way, watch which direction you are trying to throw the plate, so trying to do this is like trying to balance a pencil on each point, you just won't succeed, but this idea of ​​producing traveling fields like this It's given us an idea: if we could just produce fields traveling inwards without the plate there, then we might have the possibility of holding the plate in the middle, so let's try to do that instead of a single coil.

I'm going to use two coils, one. Inside the other is a coil and these three rings are steel rings that help strengthen the magnetic field. Now we discover that we can produce this field that travels inward if we make the current in this coil go in that direction. rotates at the same time that the current in it goes in reverse, so when we place both coils together, perhaps we can detect with the copper cylinder a very slight tendency to produce fields that travel inwards, that is, the bottom of the cylinder moves. towards the center that is what we are looking for the magnetic field does not fix on wooden, cardboard or paper fish so I can pass a piece of wood underneath without affecting the floating disk in any way now I want you to imagine that we are We've been able to take this solid structure, put it under a steamroller and roll it out until it's flattened, really flattened in this direction, let's try to imagine what that would look like.

Here is our aluminum plate and we will light it. There is our suspended aluminum. but still can't move. I can push it with my hand. It is as if we have a magnetic river without any flow. It's pretty stable but it needs something to push it, so just to demonstrate I'm going to put a little air screw in it and when I turn this on, you get your propulsion. There was a time when we thought we should put a linear motor in the center between the coils to get propulsion as well as lift and guidance, but a few months later we found out that it was all like that.

What was necessary was to divide these two coils into a set of smaller coils and we could obtain the propulsion and lifting guidance from one of the same set of coils. Now here is one row of coils and the other on the other side, but this time the coils have been divided into groups so that we can produce a traveling field as well as giving lift and guidance. What we're going to push into the magnetic river is this sheet of aluminum and we've put some tape on it so that you can see it easier because it's going pretty fast, so Mary, if you take this, please put it at the end and turn it on, we will do a demonstration now.

I'm going to switch to connections for this purpose. of the track to shoot backwards now let's see what happens to our ally in play John, you know, this back to back movement, of course, has nothing to do with passenger transport vehicles, it is more suitable for drive shuttles on looms. so I'm going to change the connections again because I would like to show you the Train. Now we are going to dress this piece of aluminum to make it look like a passenger transport vehicle. The scale of this operation is such that now traveling at the maximum speed equivalent to 250 miles per hour and if you start with this I will have to go catch it because it is quite expensive now it is possible that we will see this type of vehicle transporting passengers