this okay one more slide i'm going to stick with sarah jane back there because i because i know how to relate the average kinetic to temperature i can also relate the average speed to the temperature right now i suppose you could think of this as a derivation have i ever put a derivation on a test for you no do i intend to start no okay but it's still good for you to have some measure of understanding for where some of these things come okay i could look at my v squared average so the average velocity and i could take the square root of it because i'm interested in the average velocity now this velocity gets a special name and i don't want you to be perturbed by the name when it shows up in a problem okay it's the root mean squared velocity so it's it's mean as in average from the world of statistics right but it's you took the square root of the average velocity squared so it's root mean squared all that means is square it before you take the average and then take the do the operations in the right order but we could go back to that understanding that led us to pivniket and we could say oh yeah yeah did just solve it right relate v squared to t using pivnikit and you would have that the average velocity is the square root of 3 kb t over m well that tells me the velocity depends on temperature well it kind of makes sense doesn't it if if the temperature is the average kinetic energy if i raise the temperature i'm going to raise the kinetic energy and so the the velocity is going to go up yeah it goes up as the square root of the temperature but that's okay it tells me hey if if i've got something with higher kinetic energy but it's more massive oh more massive for the same kinetic energy is going to be a slower so that's why we see the 1 over m in there right the k is in there just to turn temperature into the right units of energy and the 3 comes along because we're in three dimensions yeah and it it always amazes me macy that if i if i ask the question what is the what's the velocity of room temperature nitrogen it's 500 meters per second the little gas molecules that surround us are smashing into us with a speed of 500 meters per second that's really fast yes if it too why do we never worry about air resistance in general physics lab downstairs well what's the fastest anything moves in the general physics lab like a meter per second yeah all the little gas molecules are very happy to just get out of the way right the the one meter per second that we have in there compared to the velocity of the molecules is irrelevant right it might as well be standing still right it's not until you start running into enough of them with your motion that seriously you begin to get uh big amounts of drag so no there's no there's no air resistance in general physics it is a distribution austin and guess what as it right it can't go less than zero right and it's got this kind of funny shape this is the maxwell boltzmann distribution of speeds right that we're not going to do much more than look at the pretty picture okay but you not surprising right if the temperature goes up what happens to the shape of the curve it kind of stretches out yes and my last thing with this is how many of you go by the mylar helium balloons because they're really cool and when you celebrate your friend's birthday please don't do that anymore okay there's a national shortage of helium and all the scientific labs are really strapped to carry on their programs because apparently we all now put helium into balloons and watch them float away through whatever yes it's a waste okay but um austin what's the majority component of air what's next that's right is there much hydrogen in the air there is not is there much helium in the air not much okay you had they they extract it but there's there's really very little why is there so little of hydrogen and helium they are light yes if they are light and i go back and look at that if i make m small what happens to v v goes up and in fact what happens is we end up with a curve like this for our hydrogens and our heliums where this is the escape velocity for anything to leave the earth's gravitational field so yes where's where is the helium and hydrogen that is currently in our atmosphere going it's going away okay so why isn't it zero well we still have hydrogen in the atmosphere because there's one lightning strike per second and most of those lightning strikes hit the ocean and if you remember your chemistry what happens when you pass large electrical currents through water what yeah it dissociates right so we're continually making it but as we make it it's going away at some point in the far for distant future the water will be gone okay you know because it will have all dissociated and the hydrogen will be gone where does helium come from helium comes from radioactive decay in the rock right it's kind of like related to the radon stuff you have so we have that decay the rocks are undergoing radio decay the helium comes up out of the ground it gradually goes through once it hits the atmosphere it goes through the atmosphere it's gone yes now yes uh is it because of the low mass it it is but it's a there's a bit of there are a couple of steps in between okay uh because it has low mass the speed of sound changes in helium and then the resonances all change because the speed is different so the resonant frequencies go up so you sound like a chipmunk right but it is ultimately related not exactly to that but so it's part of the it's part of the issue if you'd ever like to um although it's too expensive to really be serious about this we have a tank of sulfur hexafluoride in the basement well it's not so dense but it's what's its mass right so we start with sulfur where's sulfur in there 16 hexafluoride so it's got nine fluorines on it okay james earl jones okay your voice goes way down here you can sound like you know i am your father okay all right we good we are out of here that we [Music] that don't get rid of that we keep this we stopped