yey. anyway, that's how you find the wavelength of something. i can show you the slinky here. can someone grab the end of this for an "a" in the course. [laughter] right over here. now, i'm gonna take this wave and i'm gonna shake it back and forth along the direction like this. well, i'm gonna expect a little bit more. if i vibrate it like this, can you guys see that the vibrations are along the direction of travel? we have a name for that kind of wave. first, there's two kinds of wave we're gonna distinguish, longitudinal and transverse. what kind of wave you suppose it is that vibrates along? longitudinal-- along the direction of wave travel. how many say, "oh, it's probably a trick. "it'll be transverse 'cause it seems like common sense say longitudinal, right?" what's the answer, gang? - longitudinal. - longitudinal. how about if i vibrate it transverse to the direction of wave travel? it's like the kind of wave i have here. what kind of wave is that, gang? - transverse. - transverse wave. and both those ways have a wavelength, frequency, period, wave speed and the whole

a polar bear, yey, physics, huh? okay. you ever be wondering about a rainbow? why do you get all the colors in a rainbow? to understand a rainbow, first of all, you got to understand a prism. you know if a white light comes in a prism, you get different refractions? different colors refracted different amounts. it turns out you get red here maybe, green here, and blue here and sort of like that. and you guys know with a prism you can get a nice, nice spectrum. we call it a rainbow in a loose sense, yeah? but you get that in the sky too, why? well, it turns out in the sky, rather than have prisms, you have little spherical drops and those little spherical drops sort of like this. and what happens there, sunlight coming in, the white light from the sun comes in, refracts, boom, makes one reflection and then another refraction and out here would come like, red. and some bends a little differently, comes out here, this would be maybe violet. and it turns out you've got an angle between here and here of, i think it's 40 degrees for the violet. and here and here 42 d