at distinconetween-- that dtinction between weht and mass, i can kind of show you that kind of neatly with this device. what i'm gonna do is take this heavy ball-- heavy ball or massive ball? - both. - yes. both, yeah. see, i'm gonna take this ball. it's got a lot of mass, also has a lot of weight, okay? and what i'm gonna do, i'm gonna take one of these strings in the bottom. you see i'll try different trials here. and i'm gonna pull, pull, pull. i'm gonna pull, pull, pull, pull, pull, pull, until one of these strings, either the bottom one or the top one, is gonna break. and what i want you to do is i want you to guess, hypothesize, which string, the top or the bottom will break with a gradual, gradual tension increased at the bottom? check your neighbor. okay, when i pull that very, ve slowl gang, which string gon break, top or btom? - top. - top. top one? how many say the top? let's try it. [laughter] maybe newton's having a bad day. [laughter] you know what that might have been? that might have been a string before that we partially damaged. yeah. probably. can we start the tape.