Hi, there.
Did you want to create some cool physics
art without having to do any of the design yourself?
I thought so.
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We've got the square plate on the mechanical vibrator, which
is plugged into the tone generator.
This vibrates the plate at different notes,
as we change the frequency here.
I'll sprinkle a little stand on the plate.
And now, watch this.
Why does this happen?
As I tune the plate to vibrate at very specific frequencies,
or notes, the sand moves on the plate
into beautiful, though unusual, patterns.
As I find higher and higher special frequencies,
the patterns on the plate get more intricate.
How awesome is this?
But it does kind of sound like a dying ferret.
Why does it happen?
The main concept here is resonant mode.
Let's back up a little bit to the physics of waves.
In physics, a wave is a disturbance
traveling through a medium or through space.
If I constrain my median at the other end,
the wave reflects back at me.
See?
Now, if I send continuous waves down the slinky,
they also reflect back.
And what I get is two waves, one moving away from me and one
moving at me.
But, obviously, the rope can't be in both places at once.
So, as my incoming wave reflects back, I don't see both waves,
I see a combination of the two.
The waves add when they're on top of each other
and subtract when they're opposing one another.
And something crazy is happening.
You've got a wave going this way,
combined with a wave moving that way, and when they interfere,
the result is, as you might expect,
a wave that doesn't appear to be moving in any direction.
It's standing.
This is called a standing wave.
And so is this.
The places where the ways appears to be not moving at all
are called nodes.
And the places where they're moving a lot
are called antinodes.
Now that we've mastered standing waves,
let's go back to our square plate.
If you look closely, there are places
where the plate and the sand are moving a lot and places here
where they're not moving at all.
These are nodes, just like the nodes
that didn't move on our slinky.
Here are the antinodes.
And just like we needed specific frequencies
to get standing waves on are slinky,
the same is true for our plate.
These specific frequencies are called resonant modes.
And they're caused by waves traveling out from the center,
bouncing off the sides, and interfering with each other
just right so we get standing patterns.
Also, the higher frequency, the closer together the nodes,
just like the slinky.
But now, what if you did this in three dimensions?
You could have vibrations coming from the sides
and from the front and back.
And you'd get interference from all of these, such
that there would be nodes in midair, places where
the air is completely unmoving.
And you could, hypothetically, place an object there
and cause it to levitate.
That would be crazy.
But it's exactly what researchers
from the University of Tokyo and the Nagoya
Institute of technology did.
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Well, that's all I got.
Really, the physics is the cool part.
So, stay tuned to see the vibrations on these plates.
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