did you read about the difference between compressions and rarefactions? you know, when i strike this thing, the waves--boom, boom-- compressed air comes out. the compressed air, compressed air, compressed air, followed by decompressed air? watch this. now, listen. [laughter] hear that? did you hear the absence of sound? - did you hear--was that neat? - - no. i never do it more than once because i don't wanna trust my luck, but you get the idea. but i'll tell you want. let me get these things so they're a little bit different in frequency and strike them both at the same time. can you hear the throbbing? - that is a result of inter-- - ference. --interference and the phenomenon that's called-- sound. this phenomenon of pulsating-- two sounds pulsating in and out, in and out of phase is called, by the way--scholars? - beats. - beats. all right. i thought you guys were putting me on there for a while. and that's a beat. ted, can we show beats up here? hopefully show beats. so you can see as well as hear what's going on. you can see the wave form. isn't that

did you read about the difference between compressions and rarefactions? you know, when i strike this thing, the waves--boom, boom-- compressed air comes out. the compressed air, compressed air, compressed air, followed by decompressed air? watch this. now, listen. [laughter] hear that? did you hear the absence of sound? - did you hear--was that neat? - - no. i never do it more than once because i don't wanna trust my luck, but you get the idea. but i'll tell you want. let me get these things so they're a little bit different in frequency and strike them both at the same time. can you hear the throbbing? - that is a result of inter-- - ference. --interference and the phenomenon that's called-- sound. this phenomenon of pulsating-- two sounds pulsating in and out, in and out of phase is called, by the way--scholars? - beats. - beats. all right. i thought you guys were putting me on there for a while. and that's a beat. ted, can we show beats up here? hopefully show beats. so you can see as well as hear what's going on. you can see the wave form. isn't that

the rarefaction. and when it gets right here, right here, right here, right then what happens? one more time. boom. you see the next one. so it's not how hard you push. it's the rhythm with which you push that counts. do you see that? and if these are both of the same frequency-- you ever hear people talk about, "oh, someone is always on my wavelength"? they're kind of talking about that. see? if you have the same wave, same frequencies, then this one will set this into resonance. a couple of years ago about-- hey, must be five years ago now. i was skating to golden gate park. i roller skate. now, i'm skating through golden gate park and there's a kid-- saturday morning. this kid's sitting on a swing all by himself. and the kid says, "hey, mister, give me a push." i look and i see all the wet, soggy grass between me and him, i gotta clank through all the grass, get my ball bearings all wet and everything. you know, i said, "what you say, kid?" "you heard me. come over here and give me a push." you know how some of the kids act today? the kid didn't say, "i know you're busy "and