aft after we're done i'll tell you the story about the rope and the console here all right i don't want to take class time for it but all right ben do you ever play with a gyroscope as a child i have my gyroscope not anymore no i have to get my string wound around back on here come on this is the ah what's the most miraculous thing about the gyroscope it doesn't it it doesn't rotate down you read the slide very good why doesn't it rotate down that's why i put it on there all right i think we're almost ready here now and this time we'll push that through and we'll squeeze it together so that it doesn't do that and yeah why doesn't it just go boom okay it doesn't this man it doesn't fall straight down now this doesn't have a rope in it it doesn't fall down because you have a force this way this and you have a force of gravity here and it does not fall straight down because those two forces are equal right the force of gravity pulling this down and the force of the rope pulling up or the same so it does not fall down to the floor the question is why doesn't it do that right why doesn't it rotate down well it doesn't rotate down because there's an l right and the force of gravity with that l gives you a torque right what direction does the torque point well we would do our standard thing right da da da we could find the l we would say the force is trying to rotate it down but it's trying the right hand rule would say hey that torque is into the board right all right if it's into the board into the board yes into the board but we know torque equals delta l over delta t so it's trying to change the angular momentum vector that's right but what direction does the torque point right it points let's see for this one it points into the board that way so what direction is the angular momentum vector do it moves from pointing out the side of the wheel to over here it doesn't point from out the side of the wheel to here it points out the side of the wheel torque points this way so the new angular momentum vector points this way and now we do it again does the angular 1 does the torque point down no it points a little at an angle here but it then says i'm going to change the angular momentum vector from out the side of the wheel this way and the thing goes around in a circle just like what you saw it do it doesn't rotate down because there's no torque to make it rotate down there's only a torque to make it go around in a circle until friction takes over and wins and it stops and it does its thing who where are my cat lovers yes if you drop your cat does it land on its feet like 95 how does it do that yeah it does have a muscle in its spine but so what how does that make it turn over almost right there is a torque there what the what the cat does that a cat knows how to do this and you people don't i mean right what the cat does is it takes its back legs and extends them so that the back half of the cat has a very small moment of inertia and it puts its four front legs out straight okay and then it twists itself but the front doesn't twist as far as the back because the two moment of inertias are different then it does the opposite then it quickly pulls in the front and extends the back and continues this twisting motion okay and it can spin itself in space while conserving angular momentum who's next cat lover come on you can do have a seat no you're not okay what you're gonna you're gonna hold these and you're gonna swing pull them in go like this push them out swing go like this and you're going to scoot yourself in a circle come on you got to do it hard don't don't not just just your arms okay am i gonna have to do this no okay okay you're gonna push him out over to here sideways now don't hold on to me i'm not trying and then when your arms fully extended you're gonna swing sideways yeah there you go you got it yes you've got it right there's no external torque moving him is there well it doesn't work if you just go back and forth i'm not a cat now at the end of the day now stop now he has no net angular momentum right but he's able to move himself by by changing his moment of inertia and that's that's a crude variety crude variation in what the cat does with their legs yeah this could be an exercise workout all right you can put them there and i think oh yes yes the last ones okay football fans yes so uh patrick mahomes goes back and he launches that deep ball and the the football spinning right and it gets to the receiver and it's pointed like this did the angular momentum vector change it was like this now it's like this where's the torque uh good question right but there's got to be a torque somewhere and as soon as you say well it's air resistance with the laces that would mean left-handed quarterbacks the ball would go this way and that's not true turns out it's a very complicated question and my other ending thing here today is right solid aluminum i had a student's father make this because he taught casting in a community college that was that was their project to cast this odd shape spins very nicely right it only spins in one direction so you start it with angular momentum up and it turns it into angular momentum down do you believe do you believe what do you believe and and yes so if that if that changes its angular momentum vector is there a torque somewhere yes where it is is incredibly complicated but there is a torque that acts on it so that there's no torque sorry there's a torque there turns it around but the torque is not there when you spin it that way you do it