ShmoopTube

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[Dino and Coop singing]

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There are all sorts of waves out there in the world. [Girl waving]

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From the huge waves that crash onto the beach… [Wave crashing into rocks]

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…to the more modest waves that move through this dude's Slinky… [Man playing with his slinky]

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He probably should have brought more books and fewer Slinkys.

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Just sayin'.

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For all that variety, all the waves we see in the world can be classified as one of two [Examples of different waves shown]

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types: transverse waves, or longitudinal waves.

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To figure out the difference between these two types of waves, we'll need to take a detour [Man on a boat going past a math detour sign]

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into some pretty math-y concepts.

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But hey, at least math is better than being shipwrecked! [The boat then goes off a waterfall]

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To most people, that is. [Man looking happy he is stranded rather than having to do maths]

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At its most basic, a wave is a disturbance that moves through an object. [Coop pointing at a blackboard]

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That wave will be moving in a certain direction, and we call that direction the direction of

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propagation.

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Not to be confused with the "direction of Bob Agasion," which is just the direction [Bob Agasion walking down the street]

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some guy named Bob is walking.

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Hey, Bob.

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Anyway, it turns out that different waves travel differently in relation to the direction [Dino pointing at a blackboard]

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of propagation…

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…and that's where math comes into the picture!

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As you might recall, two lines are perpendicular if they meet at a 90-degree angle. [Demonstration of a perpendicular angle]

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On the other hand, two lines are parallel if they're on the same plane, but never meet.

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That is, if they're on the same geometric plane…

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…not the same transatlantic flight, where they happen to be seated across the cabin [Aeroplane in the sky]

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from each other.

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So what do these kinds of lines have to do with waves?

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Well, let's use a Slinky to find out!

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If we attach one end of the Slinky to the doorknob, and wave the other end of the Slinky up and [Person making a wave with a Slinky]

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down, we start making waves.

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Those waves move towards the doorknob.

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That means the direction of propagation is towards the doorknob! [Arrow shows the direction of propagation]

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But what are the waves up to?

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If we pay close attention to the movement of the Slinky, we see that it's moving up

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and down.

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In other words, perpendicular to the direction of propagation.

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When a wave vibrates at right angles to its direction of propagation, we call it a transverse wave. [Coop pointing at a blackboard]

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That's exactly what we've got here.

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Now, let's say we change things up a little bit.

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We keep one end of our Slinky attached to the doorknob, but instead of moving the other

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end up and down, we move it forwards and backwards, towards and away from the doorknob. [Person moving the Slinky]

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Our direction of propagation's the same…

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…but this time, instead of moving up and down, the Slinky's moving forwards and backwards:

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parallel to the direction of propagation.

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When a wave vibrates parallel to its direction of propagation, we call it a longitudinal wave. [Dino pointing at a blackboard]

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Same Slinky, different kind of wave.

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Phew!

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We've figured out how to identify transverse and longitudinal waves, and all thanks to

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the humble Slinky. [Guy mad about Slinky toys]

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See?

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Maybe that shipwrecked guy had the right idea!

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Aw…look at him waving at us….hi, buddy! [Guy being surrounded by sharks waving for help]

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What a friendly guy! [Big shark jumps out the water]

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