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Ever seen this guy before? This is a Lissajouz curve.
You get this when you have two signal generators hooked up to an oscilloscope
and they're giving out the same signal, so one is giving out 100 Hertz right now
and so is the other, and they're pretty close together,
so you get this curve here. If you change the frequency of one of them,
you can change the curve. But we just want to focus on the one to one
curve right now. I can create this mechanically,
and so can you! I'll show you!
So you can create this with tuning forks, a laser, and front surface
mirrors. Here I have a green laser shining onto
our first tuning fork. This tuning fork has a frequency of 256 Hertz,
and I actually glued onto it a very thin front-surface mirror.
The mirror had to be very thin because otherwise, when I hit it, a thick mirror would dampen
that sound. So the light is reflecting off of that mirror
and hitting this one on our second tuning fork.
So we have two front-surface mirrors, and the laser beam is reflecting off of both
of them. Notice that the two tuning forks are 90 degrees
from each other, This one is rotated,
so when I hit this one, it's gonna bend its tongs out and back.
This actually creates a cool pattern on the wall.
I'm going to hit the vertical tuning fork. It becomes a vertical line on our wall.
If I stop the tuning fork, it's just a little dot again.
Now I'm gonna hit the horizontal tuning fork. You get a horizontal line.
When I stop the tuning fork, you just get a little dot again.
Now I'm gonna hit both of them. Remember, our oscilloscope had a wave,
or something oscillating up and down, vertically, and we plotted that agaisnt something oscillating
horizontally. So let's see if we can get this.
I'll hit the vertical one first. Now the horizontal one.
Look at that! I'll see if I can focus in for you.
I'll try and do it again, but I'll start you off a little bit closer
this time. Ok?
So keep watching, I'll go hit it. Hitting the vertical one now,
Horizontal one. Notice at first, it's a little shaky,
and then you get this nice curve. I know its on the pipe so it's not so great,
but we'll try again. Now I want you to really focus on
how this thing moves, and how that correlates to the sound that
you hear. So I'm going to hit the vertical one,
horizontal one. Do you hear its quieter,
louder, quieter,
louder. So this actually shows you
when the two frequencies are in-phase or not. If you want to build this, just contact me,
um, and happy Lissajouz creating!