Physics of Skydiving: Andrew Horning at K12Live! (MIT Museum Second Fridays, 1-10-14) - By MITK12Videos
Transcript
| 00:04 | Yeah , so hi everybody , she said my name's | |
| 00:10 | Andrew , Remember the skydiving club . So at MIT | |
| 00:15 | we study a lot , but we would like to | |
| 00:17 | have gone and sometimes that's crazy , kind of fun | |
| 00:19 | uh , including skydiving . So I'm going to talk | |
| 00:23 | a little bit about the physics of skydiving for about | |
| 00:25 | 10 minutes and then we actually have some skydiving equipment | |
| 00:28 | , including a parachute that will hold up and show | |
| 00:30 | how it works . And I've got a couple more | |
| 00:32 | members of the skydiving club sitting in the back will | |
| 00:34 | come up and answer some questions too . So moving | |
| 00:41 | forward , uh , I want to talk just a | |
| 00:44 | little bit about why you actually need to be smart | |
| 00:47 | to throw yourself out of an airplane because it doesn't | |
| 00:49 | necessarily sound like a smart idea , but I'm sure | |
| 00:52 | the parents in the audience don't think it's smart at | |
| 00:54 | all for kids to be going on an airplane , | |
| 00:56 | which it's not , you need to be 18 and | |
| 00:59 | you need to get a license to do it because | |
| 01:01 | it's pretty complicated , but there's a lot of physics | |
| 01:04 | involved in this and we exploit it for our own | |
| 01:07 | amusement when we jump out of a plane . So | |
| 01:09 | really there are two major forces acting on you . | |
| 01:12 | When you jump out of a plane , there's the | |
| 01:14 | force of gravity which is pulling us down and that's | |
| 01:18 | constant . The earth is a certain size and has | |
| 01:20 | a certain amount of stuff in it . And that | |
| 01:22 | pulls us down there . Uh , there's also the | |
| 01:25 | force of drag because as you get faster and faster | |
| 01:29 | there's wind pushing back up . So the total force | |
| 01:32 | on a person falling through the sky in freefall is | |
| 01:35 | actually both of those together . Um , so we | |
| 01:37 | write in physics as the sum of those two , | |
| 01:39 | so gravity plus the drag force . So here's what | |
| 01:43 | it looks like in real life when people compete . | |
| 01:45 | There is competition Skydiving and they make formations and they | |
| 01:48 | see how many they can make in a certain amount | |
| 01:50 | of time . This particular team is really , really | |
| 01:53 | good and they can do 50 and 35 seconds Club | |
| 01:57 | , so they're all pushing against the wind to do | |
| 01:59 | these formations , you'll see their feet sticking out , | |
| 02:01 | their arms sticking out there , doing some weird motions | |
| 02:04 | that is all using the force of drag to reorient | |
| 02:07 | their bodies to move up and down a little bit | |
| 02:10 | to move forward and back so that they can make | |
| 02:12 | all of these different formations . So it's all about | |
| 02:14 | exploiting the forces that are working on you . So | |
| 02:17 | it looks like they're floating a little bit , they're | |
| 02:19 | actually falling towards the Earth . They're just really , | |
| 02:21 | really high up at this point , they're going about | |
| 02:23 | 120 mph . She's called terminal velocity and I'll talk | |
| 02:27 | about that and how you can get there . So | |
| 02:30 | the question is how fast you go get that a | |
| 02:33 | lot . Um , it has to do with these | |
| 02:35 | two forces gravity and drag . So if we write | |
| 02:38 | down the equations for it , this gravity has a | |
| 02:41 | couple parts to , it really is the mass of | |
| 02:44 | the person or thing that's falling out of the sky | |
| 02:46 | . So highway £150, that's my mask , my weight | |
| 02:51 | . And that gets acted on by the force of | |
| 02:53 | gravity , which is just relative to the thing that | |
| 02:57 | you're calling towards . So in this case of the | |
| 02:58 | Earth , if you're skydiving on the moon , you | |
| 03:00 | can go slower because there's less traffic , then there's | |
| 03:04 | another part . And this one is more complicated , | |
| 03:06 | which is the drag or the wind resistance from the | |
| 03:09 | wind uh in the air as you fall through it | |
| 03:13 | . So like when you go down the freeway in | |
| 03:15 | your car and stick your hand out the window , | |
| 03:18 | you feel a force pushing back on it . That's | |
| 03:20 | the exact same kind of force . And if you | |
| 03:22 | write down a simple form of the equation for it | |
| 03:25 | , it's got a shape component . So if I | |
| 03:27 | spread out into the wind , there's more force on | |
| 03:29 | me than if I tuck up into a ball , | |
| 03:32 | there's an area exposed to wind as well . So | |
| 03:34 | like a similar sort of thing is if I'm really | |
| 03:36 | spread out and really tucked up tightly and then there's | |
| 03:40 | a velocity component for speed . So the faster you | |
| 03:43 | go , the more wind is pushing back against you | |
| 03:45 | . So if you stick your hand out the car | |
| 03:47 | window going down the road at five miles an hour | |
| 03:50 | , There's a lot less force than if you're going | |
| 03:51 | 55 mph . So that's a velocity component that was | |
| 03:55 | actually squared . So the speed really really matters . | |
| 03:59 | So here's a break from the math and just more | |
| 04:01 | sweet videos of people jumping out of airplanes . So | |
| 04:03 | here you'll see him taking some different body positions that | |
| 04:07 | allow them to direct the forces so that they can | |
| 04:09 | actually fly forward a little bit or fly towards each | |
| 04:12 | other . So again , there's still falling here . | |
| 04:14 | They're probably going 150 mph . At this point , | |
| 04:18 | they're not wearing a suit , there's not a whole | |
| 04:19 | lot of area exposed to the wind . Um and | |
| 04:22 | they've got their arms back . So there's actually force | |
| 04:24 | pushing this direction as well as back up and believe | |
| 04:27 | it towards the ground . So like I said , | |
| 04:32 | there is a point where you can't go any faster | |
| 04:34 | . So it's called terminal velocity . You get there | |
| 04:36 | about 15 seconds into a skydive . We skydive during | |
| 04:40 | free fall for maybe 50 seconds before we golden parachute | |
| 04:43 | . We got up to about 120 miles an hour | |
| 04:46 | and then you don't go any faster . You're still | |
| 04:48 | following , you're still going really quickly or you're not | |
| 04:50 | going any faster than 120 . And that's because when | |
| 04:54 | you hit terminal velocity , the force pushing back up | |
| 04:56 | on you is the same as the force pushing back | |
| 04:59 | down on . So there's the down part which is | |
| 05:02 | negative , that's gravity pulling you towards the Earth . | |
| 05:04 | And then there's the up part that's positive , that's | |
| 05:07 | the wind pushing back against you . And at terminal | |
| 05:10 | velocity these have become the same . So when you | |
| 05:13 | add them together , there's an up and a positive | |
| 05:15 | part and a down part which is negative . When | |
| 05:17 | you add the same number that positive and negative get | |
| 05:20 | zero and there's no total force . So you're moving | |
| 05:23 | in a quick speed but there's no acceleration anymore . | |
| 05:27 | So here's a quick little graph of what it looks | |
| 05:30 | like When you jump out of a plane for the | |
| 05:32 | 1st 20 seconds or so in blue is the velocity | |
| 05:35 | of the speed in miles an hour . It goes | |
| 05:38 | from zero to negative 120 . The negative for us | |
| 05:41 | , physicist is meaning that it's pointing us down . | |
| 05:44 | So you get up to about 120 and you'll see | |
| 05:47 | you don't get any faster than that after about 20 | |
| 05:49 | seconds . This is the acceleration plotted up here , | |
| 05:52 | so it gets toward zero when your terminal velocity you're | |
| 05:56 | not going any faster . So when you start off | |
| 05:59 | , you have gravity just pulling you down . Then | |
| 06:02 | the overall total force is just the gravity heart and | |
| 06:06 | is pointing down as we jump out , The drag | |
| 06:09 | starts kicking in and it goes up and the total | |
| 06:12 | force disappears until there's none And then you're not going | |
| 06:16 | 120 mph and not going any faster . So I'll | |
| 06:19 | play that again . Just watch the ball through along | |
| 06:22 | the line . So if you're really speeding up And | |
| 06:25 | now it slows down in terms of the rate of | |
| 06:27 | change and you get stuck at 120 mph because there's | |
| 06:31 | so much wind pushing back against you , you can't | |
| 06:33 | go any faster . Mhm . Uh then of course | |
| 06:37 | at some point you want to open the parachute so | |
| 06:39 | that you don't hit the ground at 120 mph . | |
| 06:42 | And what that does is it just adds extra dread | |
| 06:45 | . So that's three an arrow pointing up . You | |
| 06:48 | had a whole bunch more area above your head and | |
| 06:51 | then there's a whole bunch more drag if you slow | |
| 06:53 | down so that it doesn't pull you upward . It | |
| 06:57 | just keeps you from going down as fast . So | |
| 07:00 | now you've got a bunch more drag and then you | |
| 07:03 | do gravity and you decelerate just by opening up more | |
| 07:07 | area to be like spreading your body extra extra wide | |
| 07:10 | . Except here you're just doing a fabric and you | |
| 07:14 | can get a little added benefit from the fancy new | |
| 07:16 | parachutes because they do get some lift like an airplane | |
| 07:18 | wing so you can actually control these things and floods | |
| 07:21 | very precisely once they're opened up like that and land | |
| 07:24 | wherever you want , mm hmm . And then of | |
| 07:27 | course people get fancy , you don't have to do | |
| 07:29 | it on your stomach . These people can go ahead | |
| 07:31 | first feet , first , any sorts of body positions | |
| 07:34 | like that are controllable at this point , there's not | |
| 07:36 | as much area exposed to the wind . It's mainly | |
| 07:39 | just his head on his shoulders and maybe a bit | |
| 07:41 | his leg . So he's probably going to 100 miles | |
| 07:43 | an hour at this point because there's a lot less | |
| 07:46 | drag . He eventually stops going any faster . But | |
| 07:49 | when he gets to that point It's a lot it's | |
| 07:53 | a higher speed . So it's like 200 mph for | |
| 07:56 | these sorts of people and you can push against that | |
| 07:58 | wind once you've got it up there and flip over | |
| 08:00 | move forward move backward all just by using these forces | |
| 08:03 | that you've got in the sky pushing back against you | |
| 08:08 | . Yeah . Mhm . Yeah that's all they had | |
| 08:15 | in terms of presentation . Um We'll bring up actually | |
| 08:18 | a parachute and some equipment and you guys can ask | |
| 08:20 | you some questions because we've got about five or 10 | |
| 08:23 | 1 minutes . If you have questions about scott . | |
| 08:25 | Having want us to walk you through a parachute looks | |
| 08:27 | like um One question we get a lot . I'm | |
| 08:31 | wearing one of these jumpsuits . You don't have to | |
| 08:33 | be wearing a jumpsuit . It just gives us a | |
| 08:35 | more reliable thing for the wind to push against and | |
| 08:37 | so it's easier to do formations and I have more | |
| 08:42 | reliable service push against . Yeah . I'll point out | |
| 08:46 | how these guys work . So this is actually two | |
| 08:48 | parachutes in a container like this . There's a main | |
| 08:51 | one down here . That's what you would open up | |
| 08:53 | and if anything goes wrong , which doesn't happen very | |
| 08:55 | often . But we want to be extra careful because | |
| 08:58 | we're plummeting towards the ground at 120 miles an hour | |
| 09:00 | . There's a backup one up here . So it's | |
| 09:04 | possible if the main one has something wrong with a | |
| 09:07 | little tear , gets tangled to get rid of the | |
| 09:09 | main parachute and go immediately to the backup . So | |
| 09:13 | there's a bunch of handles on this thing to open | |
| 09:15 | the main one . You throw this one out into | |
| 09:17 | the wind . It's got a tiny parachute on it | |
| 09:19 | . It goes away from you and then it opens | |
| 09:21 | up the big one as you saw in the video | |
| 09:23 | . Then everything slows down because you've got a bunch | |
| 09:25 | of extra drag . If the main one has a | |
| 09:28 | problem , you can get rid of it with this | |
| 09:30 | handle and then go to the back of one with | |
| 09:33 | that handle . Of course , you're going 120 miles | |
| 09:35 | an hour . So that's 1000 ft and 5.5 seconds | |
| 09:38 | . So you want to be able to do that | |
| 09:40 | pretty quickly . If anything's going wrong , we pull | |
| 09:43 | the parachute about three or 4000 ft above the ground | |
| 09:46 | . So you have maybe 20 seconds before you would | |
| 09:49 | hit the ground if you want to do anything about | |
| 09:51 | it . So these are really reliable . Way safer | |
| 09:55 | than it seems now . There's a lot of technology | |
| 09:57 | in these , uh , in addition now they put | |
| 10:00 | computers in there that sends how high you are and | |
| 10:03 | how fast you're going . It's his underneath his flat | |
| 10:06 | up there . So if you passed out or forgot | |
| 10:09 | to open the parachute , for some reason , there's | |
| 10:12 | something seriously wrong , it would open it for you | |
| 10:15 | because it knows how fast you're going and it knows | |
| 10:17 | how high you are . So if you really had | |
| 10:22 | to , it'll just open it for you right before | |
| 10:24 | you hit the ground . So there's extra backups of | |
| 10:27 | these things too . But yeah , it's not very | |
| 10:28 | big . And then we of course learned to pack | |
| 10:31 | these and properly care for them . And then all | |
| 10:34 | the procedures for opening and closing them in the air | |
| 10:38 | . We practice a bunch of times and that's really | |
| 10:40 | what one looks like you don't see them . Does | |
| 10:44 | anybody have any questions ? So once you open the | |
| 10:49 | parachute , It really depends on the size of the | |
| 10:52 | parachute and flight characteristics of it . Maybe you're going | |
| 10:55 | towards the ground at 20 mph or so . You | |
| 10:59 | can turn that lift or the the lift that you | |
| 11:01 | have from the parachute into a stall . So you | |
| 11:05 | can sort of pull it up right before you land | |
| 11:07 | in the actual landing . You're not going great . | |
| 11:10 | Basketball toys stepping off a table . There's something so | |
| 11:14 | it sort of depends on how you're flying in pairs | |
| 11:16 | . You can help me get . Yeah , Michael | |
| 11:22 | , they have parachutes on the airplane . Yeah . | |
| 11:25 | Let's just say the airplane line when you reach a | |
| 11:29 | certain altitude , shouldn't they have those where people can | |
| 11:34 | jump out and release the pressure on the plane and | |
| 11:37 | then everybody jumped out . Yeah , fortunately , airplanes | |
| 11:41 | are so well engineered that any situation where it would | |
| 11:44 | be useful to have a parachute almost never happens . | |
| 11:47 | Like there may be has been one or two airplane | |
| 11:50 | incidents where parachute would have helped . So I think | |
| 11:53 | that's really the reason it's just not worth it and | |
| 11:56 | it does require , so it looks reasonably straightforward in | |
| 11:58 | the videos . But even jump on your own , | |
| 12:01 | you need to do 25 skydives with instructors so you | |
| 12:05 | learn how to stay stable and open the parachute correctly | |
| 12:07 | so most people wouldn't know how to use them . | |
| 12:10 | It's a rash . Yeah . Right . Uh , | |
| 12:14 | just add a little something that they're actually a lot | |
| 12:16 | of instances of planes full of skydivers and having all | |
| 12:19 | functions and the skydivers are wearing parachutes , but they're | |
| 12:22 | not able to get out of the plane because it's | |
| 12:24 | spinning so fast and what's the planes started really having | |
| 12:27 | problems . It's going down you can't even get out | |
| 12:29 | of it . So these are gonna experienced skydivers with | |
| 12:31 | hundreds of thousands of jumps and they're already wearing parachutes | |
| 12:34 | and they still aren't able to get a plane crashes | |
| 12:36 | . So they're the one into the other question is | |
| 12:42 | yet . Yeah . Yeah . Yeah we're regulated just | |
| 12:53 | like airplanes are under a parachute . So there's specific | |
| 12:58 | zones uh where you're clear to skydive . So we | |
| 13:01 | typically go up near the new Hampshire border . There | |
| 13:03 | is also a place in the orange massachusetts where people | |
| 13:06 | go a lot uh you do have to check in | |
| 13:09 | to with the FAA to let them know they're gonna | |
| 13:12 | be skydivers mainly . So other airplanes don't fly through | |
| 13:15 | the space all your parachute because they have engines and | |
| 13:18 | we don't so they're going to win most of the | |
| 13:22 | time . So you have to get it clear , | |
| 13:24 | you can do it in the most different places . | |
| 13:26 | But like if they jump into a red sox game | |
| 13:28 | , they've done that ahead of time and everybody knows | |
| 13:33 | , Yeah , I was the computer sense of how | |
| 13:36 | you are . You take that one sure . Yes | |
| 13:40 | , there's actually a little pressure sensor in there . | |
| 13:41 | Um so he says , while you're on the ground | |
| 13:44 | at the start of your day , you turn it | |
| 13:46 | on and it calibrates to that ground pressure and says | |
| 13:48 | , okay , that is the ground model , wherever | |
| 13:51 | you turn it on . Uh and then as you're | |
| 13:53 | jumping , it senses the difference in the air pressure | |
| 13:55 | and uses that to calculate what altitude you are above | |
| 13:59 | the ground level , that you calibrated it . Um | |
| 14:02 | and then it just tracks how fast that changes to | |
| 14:05 | figure out how fast you're going down . And if | |
| 14:07 | you're going down too fast and you're at like 1000 | |
| 14:11 | or 1500 ft off the ground , uh , then | |
| 14:14 | fires a little explosive that actually bursts out your reserve | |
| 14:17 | parachute . So you kind of calibrated on the ground | |
| 14:21 | the whole every day . It's pretty Sergent . Yeah | |
| 14:25 | . But yeah , it's all based on the fact | |
| 14:27 | that there's less air pressure on top of thunder is | |
| 14:29 | down here and it's not a whole lot . But | |
| 14:31 | it's enough that we can sense it . And Banks | |
| 14:33 | here has actually built his own altimeter because he's a | |
| 14:38 | mechanical engineer does all this time . The other questions | |
| 14:43 | . Joint problem . Yeah . What's the percentage of | |
| 14:48 | failures of these parachutes ? Yeah , that's a great | |
| 14:51 | question . So the numbers I hear are maybe your | |
| 14:54 | chances of having to use the backup are about one | |
| 14:58 | in 700 . So there's a chance that there's going | |
| 15:01 | to be something wrong with the main one . It's | |
| 15:03 | about one in 700 times . Um and then the | |
| 15:07 | backup parachute , we actually can't pack ourselves . It's | |
| 15:09 | packed by somebody whose job is to pack backup parachutes | |
| 15:12 | has been repacked and expected every six months . So | |
| 15:15 | the failure rate on those is even lower . There's | |
| 15:18 | no real good estimate because people don't use them very | |
| 15:20 | often . So it's maybe one in three over 4000 | |
| 15:23 | times that we have a serious problem . Yeah , | |
| 15:27 | yeah . Uh what was that ? Uh Yeah . | |
| 15:37 | So uh the parachute is actually designed to open somewhat | |
| 15:40 | slowly , which sounds counterintuitive , but it could be | |
| 15:43 | a big force just opening and having that much drag | |
| 15:45 | all at once . So it opens in stages , | |
| 15:48 | it takes about 3-5 seconds for the parachute to open | |
| 15:51 | . And so uh it's sort of a pull on | |
| 15:54 | the hardest that you're wearing but it's really nothing substantial | |
| 15:56 | . People people do it at all ages . There | |
| 15:59 | was just 100 year old Skydiver recently . So it's | |
| 16:02 | designed so that it gets away from you and it | |
| 16:04 | sort of opens over a couple of seconds so that | |
| 16:06 | spreads it out over time . Yeah fine . Is | |
| 16:09 | there any safety features are playing to have like later | |
| 16:11 | on ? Like what like what kind of meat ? | |
| 16:16 | Mhm . Yeah . Yeah . There's been a lot | |
| 16:19 | of development lately in terms of ways to get rid | |
| 16:23 | of the main parachute and go to the back up | |
| 16:25 | . Like the main parachutes are really safe now . | |
| 16:28 | Um And part of it has been designing new cutaway | |
| 16:32 | mechanisms . Uh what really made Scott having much safer | |
| 16:35 | with the ability to go from the possibly messed up | |
| 16:39 | main parachute to the reserve parachute . And there's the | |
| 16:42 | series of rings up here uh which were developed in | |
| 16:46 | the 70s , which sort of disconnect everything completely . | |
| 16:49 | So the main parachute is now completely away from you | |
| 16:51 | before you open up a good backup one . So | |
| 16:54 | that's been a big thing . There's also a little | |
| 16:55 | line here such that when you cut away the main | |
| 16:59 | parachute , it can help open the back up so | |
| 17:02 | you don't actually have to use this other handle sometimes | |
| 17:04 | . So that's been that's been the newest thing . | |
| 17:07 | Yeah , no , we the pilot requires oxygen about | |
| 17:16 | 14,000 ft . And so since we slide open a | |
| 17:19 | giant , work ourselves out the plane , there's not | |
| 17:22 | extra oxygen in that plane . So typically it's 14,000 | |
| 17:25 | ft . We open the parachute about 3000 . But | |
| 17:30 | you can't go higher . If you have a supply | |
| 17:32 | of oxygen in the plane , it just starts getting | |
| 17:34 | really cold up there . Yeah , Yeah . Very | |
| 17:38 | well , you're skydiving . You also need the oxygen | |
| 17:41 | . So the requirements , I think you need to | |
| 17:45 | breathe oxygen in the plane if you're above eight or | |
| 17:47 | if you're between 14 and 18,000 ft . And if | |
| 17:50 | you jump out above 18,000 ft , there's not related | |
| 17:53 | , reasonable oxygen up there . So you need a | |
| 17:55 | bottle of oxygen breathing . Yeah . What do you | |
| 17:59 | do with the change in pressure ? Like Yeah , | |
| 18:02 | so you can breathe normally while skydiving . So for | |
| 18:06 | the most part you clear out your ears yourself and | |
| 18:09 | it doesn't require a lot of extra effort . Some | |
| 18:11 | people um if you have a log like stuffy nose | |
| 18:14 | there something it could be a problem . Uh So | |
| 18:17 | I don't jump if I have a cold , like | |
| 18:19 | a stuffy nose just because it's a pretty big pressure | |
| 18:22 | changed . And so a lot of the same ways | |
| 18:24 | that scuba divers used to clear their ears , holding | |
| 18:26 | your nose and blowing event to copy your terms back | |
| 18:29 | out . People do that sort of stuff uh depending | |
| 18:32 | on how sensitive they are to it . Yeah . | |
| 18:37 | Thank you . Is this a whole , we'll probably | |
| 18:40 | call you guys again . Yeah , I mean it's | |
| 18:51 | scary the first few times . It is really scary | |
| 18:56 | . Yeah . Yeah . So . Mhm . You | |
| 19:01 | have to see skydiving planes to understand , but I | |
| 19:04 | think we actually trust our parachutes more than the planes | |
| 19:06 | that we fly up because these planes are flying up | |
| 19:10 | continuously all day every day . We may not have | |
| 19:12 | the best maintenance and all that . Kind of got | |
| 19:15 | some duct tape in places and calling out because they | |
| 19:19 | know everyone's gonna jump out of it before him anyway | |
| 19:21 | . So a lot of people trust their parachutes more | |
| 19:24 | than the places , but that high up , it | |
| 19:28 | really is more like floating than falling . So you | |
| 19:31 | don't get that roller coaster feeling . So really , | |
| 19:34 | as long as you can mentally ignore what you're about | |
| 19:37 | to do at the door , playing for a minute | |
| 19:40 | or two , Then people do it . And I | |
| 19:44 | don't know why people seek this out . I mean | |
| 19:46 | I've been almost 300 times . Um , so after | |
| 19:51 | the first few , it's not so scary , but | |
| 19:53 | it definitely , it definitely takes some sort of weird | |
| 19:57 | ignorance to do in the first few times . Uh | |
| 20:01 | , Yeah , I mentioned close . So , uh | |
| 20:05 | , parachutes aren't cheap . Uh , you don't want | |
| 20:07 | to buy the use one off craigslist because they're kind | |
| 20:11 | of important parachute like this maybe slightly used or in | |
| 20:15 | basic colors , probably cost three or $4,000 . You | |
| 20:19 | can sell it back when you're done at about the | |
| 20:21 | same price . Um , so it's an investment . | |
| 20:23 | Uh scott has for me cost $27 a jump . | |
| 20:27 | So that's not too bad . Uh , going the | |
| 20:30 | first time attached when instructors maybe more like $200 because | |
| 20:34 | the instructor is very experience . And so it's it's | |
| 20:37 | definitely not cheating , sort of on par with stupid | |
| 20:41 | . I think Maybe one more question you can . | |
| 20:48 | Mhm . Mhm . Do it again . All right | |
| 20:52 | , well , great . Thank you guys again . | |
| 20:58 | What your parents about ? |
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