you've got enough left over so that the part just left over is you. but that was a big problem getting with-- how do you enter the air at 18,000 miles per hour. that's a lot of friction gang, a lot of friction, burn you up. but these problems have been solved and we live at a time now where it's routine. interesting things about the elliptical path. this circle is an elliptical path and remember we talked about an ellipse? an ellipse is an oval-shaped type thing with a focus here and a focus here, remember that? and for the case of satellite motion, one focus is the planet itself and the other focus is just in space and around it goes. maybe a higher speed will put this focus over here or further down and further down, okay? over here, even a circular orbit is an ellipse

and if i go at a higher speed, now the focus--instead of having both foci together, the bottom focus is maybe right here. these foci will move as my friend ted bredstrom just told me a while ago, just got some illumination from my tas that that focus, these foci here just move along this dotted line and the faster you go, the more this focus here goes out, out, out, out, see? we're now, is we're down here, yeah? but here's an interesting thing too a lot of people don't know about. even up in here where you're just throwing it and it hit the ground. we all learned to call this a parabola, but you know what? it's a segment of an ellipse, because if that ground weren't there, it would go in an elliptical path with this focus, the center of the earth being the far focus and some nearer focus up here. and if you throw it faster, okay? it'll follow a wider ellipse with this again the focus here

and this one over here, closer in here. and as you get closer and closer to a circle, this keeps moving right down till they're both together and now you get the special case of a circle and beyond that, then this one here just kinda move down there. and so that parabolic path is part of an ellipse. if i fire it faster than 9, it'd shoot out like that, maybe that's 10, maybe that's 11 and at 11, it'll... see it up there, see it, see it, see it? guess how fast it comes by? 11. now i'm gonna fire it at 11.2. goodbye, bye-bye, honey. 11.2, ain't gonna come back. 11.2 gonna outrun gravitational pullback, it's gonna outrun it, gonna escape.

that's the escape speed. go at 11.2 kilometers per sec, 25,000 miles an hour if you wanna translate it. go 25,000 miles an hour, goodbye, honey, you're gone. you don't come back to the earth. then you orbit around the sun. if i get way out in the edge of the solar system and i take a rock and i say, hey, earth, i see you down there, honey. and i take the rock and i, here we go. and that rock crashes into the earth by virtue of earth gravity. how fast did that rock hit? is there a upper limit? what's the fastest that rock gonna splatter into the ground? let me tell you one of the neat things about being a teacher. i keep learning elementary physics a little bit more and more every year.

if you had asked me that question several years ago, i would say, well, it would approach the speed of light and i didn't know what i was talking about, because the answer is much more elegant than the speed of light. let me give you a hint. if you're at the top of a building and i throw a rock as fast as i can to get to you and let's suppose i wanna escape the sky or something and you're at the top here and to escape the sky or something, i gotta throw at maybe 11.2 meters per second and it just gets to you and you catch it. that's how fast i gotta throw it to get it up there, all right? it's an easy question for you guys to answer when i say, if i take that rock and i just get up there and i drop it, hey, you catch it now, honey. how fast is it gonna be going when i catch it? same, right? now i gotta question for you. the first question, you're out there beyond pluto.

hey, earth, how are you doing down there, honey? you take a rock and you drop it. let it fall to earth by earth's gravity. get the sun out of the way, okay? just by earth's gravity. splat. i'll bet you're sitting next to someone who knows what the speed of the splat is, at least the upper speed, check it out. what's the maximum falling speed for planet earth? what's the answer, gang? 11.2 kilometers. 11.2 kilometers per second, right on. it's gonna be the same speed it takes to escape. how fast it has to go to get out there will be how fast it would fall back in again 'cause what slows it down-- hey, hey, hey, and it all ties together. are you ready for quiz that'll take care of all of mechanics? a little sample quiz, here we go. look over here, folks. here's a satellite going around in elliptical orbit around the earth. i'm gonna ask you a bunch of questions and see if you can answer the questions.

at what point a, b, c, d is the gravitational force that acts on that satellite a maximum? here, here, here or here? write on your paper a 'a,' a 'b,' a 'c,' or a 'd'. or if you think the gravitational force on the satellite is the same everywhere, then you write down a 'e.' same, same, right? nobody's gonna write down e for that one. in fact, what do we put down for an answer, gang? a, 'cause it's closer. b, huh? okay. number 2: at what point in the orbit does that satellite get the maximum speed? a, b, c, d or the same everywhere, e, it's an ellipse. question number 3: at what point in orbit does that satellite have the maximum velocity?

what, i got the maximum speed-- number 4: at what point in orbit does that satellite have the maximum kinetic energy? a, a, a. how many say, oh, probably where it's going slowest? come on, where's the maximum kinetic energy? - a. - huh, a? is it a? well, that means the maximum speed at 'a', all as? we like all as, yeah? number 5: where does that cast satellite have the maximum momentum? e. how many say, oh, it probably got the maximum amount where the earth's going slow? come on, nobody say that. at what point in the sky does that satellite have the maximum potential energy? gravitational potential energy.

off the as, honey, onto the what? - c. - c, huh? at what point in the sky does that satellite have the maximum total energy? that's potential and kinetic energy together. a? what would you use, gang, huh? a. at what point in orbit does that satellite have the maximum acceleration? maybe it's time to use the equation as a guide to thinking. maybe it'll have the maximum 'a' where it has the... will you be getting it? can you handle these questions? if you can, you can be handling mechanics.

can i give you the granddaddy? at what point in orbit does the satellite have the greatest angular momentum? that's the mass of the satellite times its speed times its radial distance from the earth. where is it maximum, a, b, c, d or e? think about that. you know what? that's physics. i'll catch you later.