Today I'm looking at some
strange properties of a magnet
and this is used in some device you have around the house
in fact all of you have probably seen 1 since the day you were born
and you probably got one or more around the house
you use it every day but it's one of those things that we never think about
and it has to do with the properties of a
spinning magnet and how they affect things around it
and it can do some pretty weird things
Let's get started. I will say right now when I was making this video
that this kind of looks like it might be safe and no big deal but a
the drill press can grab things and it did. The magnet can grab things and throw them
so I don't recommend doing this for safety sake
just watch and enjoy the video
See if you can guess the device is that
is in your house that uses this strange property
and at the of the video I'll show you what that is
okay so what can we do with this spinning magnet? Let's start out with an ordinary
aluminum can. I cut the top out of it.
And we'll see what it will do. I have to keep it from hitting (the magnet).
The aluminum can will spin around.
Ordinary aluminum can.
Not normally magnetic at all
You're saying, "maybe it's the air currents spinning around here". Well
We can check that. You can see
there's not much in the way of air currents.
Let's look at this one. This is just a piece of aluminum.
Aluminum with a brass screw.
and
Normally you'd say nothing's going to happen, right?
Take a piece of plastic pipe. Put this in here and if I'm very careful
It spins.
There's nothing magnetic about the aluminum.
I can stop it, show that I'm not touching it.
It does not like to stop.
And yet it is magnetically coupled to the aluminum.
In fact it will do strange things even when the magnet's not inside
For this part of the video I put a piece of white tape on here.
So you can see this spinning. This magnet is just sitting on the shaft
It can slip, the shaft is steel
so the magnet likes to stick to it, but when there's too much pressure it will slip
and that's important. I've got this "v" block which is just a big chunk of aluminum
and you can see it's not magnetic at all
but it does some weird things when it
comes in contact with a spinning magnetic field from this
I'm not touching this... on purpose anyway
You can hear it slipping
What I've got is an eddy current circulating in here
and it's creating a magnetic field of its own
and its "fighting" with the magnetic field
that's coming out of this. So when the hit each other
and since this one can slip... it does.
and even odder
when I do this side back here
It tries to the "v" block away
I wish I could show you the feeling, it is very odd
This piece of aluminum should not be doing anything with a magnet, right?
But it does.
Maybe you guessed what the common object is that you have around your house.
It's a speedometer. I built a model one here
so we can see how it does word and IF it does work
Here's our model speedometer. It's got a popsicle stick for
the indicator. Here's our brass screw from
earlier. Go around the back side. Here's the aluminum fork
that we showed earlier. There's the brass screw going through there
here's some thread tied on to the
brass screw and at the other end of that thread
is a weight and it will act as a spring to
pull our needle back to the zero position
Then of course our spinning magnet
The spinning magnet we will put between these forks
and normally
this would be coming from the wheel of your motorcycle or
from the from the wheel of your bicycle in the case of older speedometers
or from the transmission of your car
and it will spin around inside the fork
The fork will turn and the faster the magnet spins the
more this will pull and the higher the indicator
will go. And let's see if it really works.
Starting to move a little bit.
There we go
Very sensitive, very sensitive.
Now we're cruising along.
Little faster.
And stop. And there you have it
Our crude but working model of a speedometer
mechanical tachometer. Hope you found it interesting