Demos: Gyroscopes

when one wants to know their orientation or which way is down they might use a level or a plumb bob and these work great if you're in an inertial reference frame but as soon as you start twisting turning or accelerating they twist turn in accelerate to pointing in the direction of the effective gravity thanks to conservation of angular momentum a gyroscope will attempt to maintain its orientation even while accelerating now we'll look at a few more examples of gyroscopes and their strange behaviors including these since the gyroscope maintains its orientation as the world around it shifts a vehicle can determine its orientation by measuring the angle that its gyroscope makes if you put a gyroscope inside an aircraft you can use it to determine your orientation to the ground I have here a navigational gyroscope pilfered from the US Army Air Force didn't they dissolve in the 40s the gyroscope is hooked up to two potentiometers one on each axis so as the orientation changes their resistance changes with a simple voltage divider circuit we can measure the angle electronically ultimately the easiest way to see how a gyroscope maintained its orientation is with a 3-axis gimbal this gimbal allows the gyroscope to spin on all three axes so if the gyroscope starts in one orientation no matter how much we turn the rest of the gimbal or what it's sitting on the gyroscope will keep pointing in the same direction this is the same gimbal that Fineman used when he was teaching now that it's rotating along this axis it's going to want to stay rotating on that axis and it's going to maintain that orientation no matter which way I twist these outer rings here we have a gyroscope in a box a little practical joke we can spin up the gyroscope and then if someone tries to carry this box around it kind of behaves erratically in their hands [Music] now we just need an unwitting dullard to carry the box for us how about you yeah sure I'll do it well it probably feels weirder than it looks procession occurs when an object that was previously rotating on one axis begins to rotate on another axis as well this often happens when some torque kicks it off of its original axis conservation of angular momentum will want it to keep spinning along that axis even though the object's axis has turned you'll note the higher the starting angular momentum the slower the precession so even a small gyroscope like this can maintain its orientation very well if we get it spinning very fast and because it wants to maintain its angular momentum so much it'll behave oddly whenever it topples even though it looks like it should just fall over and you'll momentum keeps it moving in a circle you've likely seen this if you've spun atop and watched it spin and wobble as it falls over [Music] how an object processes is probably going to be easier to tell when we use this bike wheel gravity is naturally going to want to force the wheel down into this position as with when I held the bike wheel if it's spinning like this its angular momentum this way is zero so when it falls it's going to want to maintain that zero angular momentum but we can see that it's spinning this way so wheel itself is going to have to spin this way to counteract that as it falls [Applause] [Applause] by putting our flywheel on a couple of moving arms we have a few additional tricks we can pull you can see how it's pretty well disconnected from outside torques but if I try and spin it around this axis [Laughter] I can raise it and lower it by unbalancing it we can see some general procession and by adding a quick jolt of angular momentum we can see nutation which is periodic movement in addition to its current spinning you'll also notice that if I stop it's precession [Applause] it simply Falls because it cannot maintain its angular momentum

Channel: Caltech's Feynman Lecture Hall

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Id: 6tFzzSG8SU0

Length: 8min 13sec (493 seconds)

Published: Thu Dec 12 2019