WEBVTT 00:00:14.000 --> 00:00:18.000 Some superheros can move faster than the wind. 00:00:18.000 --> 00:00:20.000 The men in Apollo 10 reached 00:00:20.000 --> 00:00:21.000 a record-breaking speed 00:00:21.000 --> 00:00:24.000 of around 25,000 miles per hour 00:00:24.000 --> 00:00:25.000 when the shuttle re-entered 00:00:25.000 --> 00:00:28.000 the Earth's atmosphere in 1969. 00:00:28.000 --> 00:00:30.000 Wouldn't we save a lot of time 00:00:30.000 --> 00:00:32.000 to be able to move that fast? 00:00:32.000 --> 00:00:34.000 But, what's the catch? 00:00:34.000 --> 00:00:36.000 Air is not empty. 00:00:36.000 --> 00:00:38.000 Elements like oxygen and nitrogen, 00:00:38.000 --> 00:00:40.000 even countless dust particles, 00:00:40.000 --> 00:00:42.000 make up the air around us. 00:00:44.000 --> 00:00:47.000 When we move past these things in the air, 00:00:47.000 --> 00:00:48.000 we're rubbing against them 00:00:48.000 --> 00:00:49.000 and creating a lot of friction, 00:00:49.000 --> 00:00:51.000 which results in heat. 00:00:51.000 --> 00:00:53.000 Just like rubbing your hands together warms them up 00:00:53.000 --> 00:00:55.000 or rubbing two sticks together makes fire, 00:00:55.000 --> 00:00:57.000 the faster objects rub together, 00:00:57.000 --> 00:00:59.000 the more heat is generated. 00:01:01.000 --> 00:01:04.000 So, if we're running at 25,000 miles per hour, 00:01:04.000 --> 00:01:08.000 the heat from friction would burn our faces off. 00:01:09.000 --> 00:01:11.000 Even if we somehow withstood the heat, 00:01:11.000 --> 00:01:12.000 the sand and dirt in the air 00:01:12.000 --> 00:01:14.000 would still scrape us up 00:01:14.000 --> 00:01:15.000 with millions of tiny cuts 00:01:15.000 --> 00:01:17.000 all happening at the same time. 00:01:19.000 --> 00:01:22.000 Even seen the front bumper or grill of a truck? 00:01:22.000 --> 00:01:23.000 What do you think all the birds and bugs would do 00:01:23.000 --> 00:01:27.000 to your open eyes or exposed skin? 00:01:31.000 --> 00:01:33.000 Okay, so you'll wear a mask 00:01:33.000 --> 00:01:35.000 to avoid destroying your face. 00:01:35.000 --> 00:01:36.000 But, what about people in buildings 00:01:36.000 --> 00:01:39.000 between you and your destination? 00:01:39.000 --> 00:01:41.000 It takes us approximately one-fifth of a second 00:01:41.000 --> 00:01:43.000 to react to what we see. 00:01:43.000 --> 00:01:45.000 By the time we see what is ahead of us 00:01:45.000 --> 00:01:46.000 and react to it - 00:01:46.000 --> 00:01:47.000 time times velocity equals distance 00:01:47.000 --> 00:01:48.000 equals one-fifth of a second 00:01:48.000 --> 00:01:50.000 times 25,000 miles per hour 00:01:50.000 --> 00:01:51.000 equals 1.4 miles 00:01:51.000 --> 00:01:53.000 - we would have gone past it 00:01:53.000 --> 00:01:56.000 or through it by over a mile. 00:01:56.000 --> 00:01:57.000 We're either going to kill ourselves 00:01:57.000 --> 00:02:00.000 by crashing into the nearest wall at super speed 00:02:00.000 --> 00:02:02.000 or worse, if we're indestructible, 00:02:02.000 --> 00:02:04.000 we've essentially turned our bodies into missiles 00:02:04.000 --> 00:02:08.000 that destroy everything in our path. 00:02:08.000 --> 00:02:11.000 So, long distance travel at 25,000 miles per hour 00:02:11.000 --> 00:02:12.000 would leave us burning up, 00:02:12.000 --> 00:02:13.000 covered in bugs, 00:02:13.000 --> 00:02:16.000 and leaves no time to react. 00:02:16.000 --> 00:02:17.000 What about short bursts 00:02:17.000 --> 00:02:18.000 to a location we can see 00:02:18.000 --> 00:02:20.000 with no obstacles in between? 00:02:20.000 --> 00:02:22.000 Okay, let's say a bullet 00:02:22.000 --> 00:02:26.000 is about to hit a beautiful damsel in distress. 00:02:26.000 --> 00:02:28.000 So, our hero swoops in at super speed, 00:02:28.000 --> 00:02:29.000 grabs her, 00:02:29.000 --> 00:02:32.000 and carries her to safety. 00:02:32.000 --> 00:02:34.000 That sounds very romantic, 00:02:34.000 --> 00:02:36.000 but in reality, that girl will probably suffer 00:02:36.000 --> 00:02:38.000 more damage from the hero than the bullet 00:02:38.000 --> 00:02:40.000 if he moved her at super speed. 00:02:40.000 --> 00:02:44.000 Newton's First Law of Motion deals with inertia, 00:02:44.000 --> 00:02:46.000 which is the resistance to a change 00:02:46.000 --> 00:02:48.000 in its state of motion. 00:02:48.000 --> 00:02:49.000 So, an object will continue moving 00:02:49.000 --> 00:02:51.000 or staying at the same place 00:02:51.000 --> 00:02:53.000 unless something changes it. 00:02:53.000 --> 00:02:57.000 Acceleration is the rate the velocity changes over time. 00:02:57.000 --> 00:02:58.000 When the girl at rest, 00:02:58.000 --> 00:03:00.000 velocity equals zero miles per hour, 00:03:00.000 --> 00:03:02.000 begins accelerating to reach the speed within seconds, 00:03:02.000 --> 00:03:04.000 velocity increases rapidly 00:03:04.000 --> 00:03:06.000 to 25,000 miles per hour, 00:03:06.000 --> 00:03:09.000 her brain would crash into the side of her skull. 00:03:09.000 --> 00:03:12.000 And, when she stops suddenly, 00:03:12.000 --> 00:03:14.000 velocity decreases rapidly to zero miles per hour, 00:03:14.000 --> 00:03:17.000 her brain would crash into the other side of her skull, 00:03:17.000 --> 00:03:22.000 turning her brain into mush. 00:03:22.000 --> 00:03:25.000 The brain is too fragile to handle the sudden movement. 00:03:25.000 --> 00:03:27.000 So is every part of her body, for that matter. 00:03:27.000 --> 00:03:30.000 Remember, it's not the speed that causes the damage 00:03:30.000 --> 00:03:32.000 because the astronauts survived Apollo 10, 00:03:32.000 --> 00:03:34.000 it's the acceleration 00:03:34.000 --> 00:03:35.000 or sudden stop 00:03:35.000 --> 00:03:37.000 that causes our internal organs 00:03:37.000 --> 00:03:38.000 to crash into the front of our bodies 00:03:38.000 --> 00:03:40.000 the way we move forward in a bus 00:03:40.000 --> 00:03:42.000 when the driver slams on the brakes. 00:03:43.000 --> 00:03:45.000 What the hero did to the girl 00:03:45.000 --> 00:03:47.000 is mathematically the same as running her over 00:03:47.000 --> 00:03:50.000 with a space shuttle at maximum speed. 00:03:50.000 --> 00:03:53.000 She probably died instantly at the point of impact. 00:03:53.000 --> 00:03:56.000 He's going to owe this poor girl's family an apology 00:03:56.000 --> 00:03:59.000 and a big fat compensation check. 00:03:59.000 --> 00:04:02.000 Oh, and possibly face jail time. 00:04:02.000 --> 00:04:04.000 Doctors have to carry liability insurance 00:04:04.000 --> 00:04:06.000 just in case they make a mistake and hurt their patients. 00:04:06.000 --> 00:04:10.000 I wonder how much superhero insurance policy would cost. 00:04:11.000 --> 00:04:14.000 Now, which superpower physics lesson 00:04:14.000 --> 00:04:16.000 will you explore next? 00:04:16.000 --> 00:04:21.000 Shifting body size and content, 00:04:21.000 --> 00:04:22.000 super speed, 00:04:22.000 --> 00:04:24.000 flight, 00:04:24.000 --> 00:04:27.000 super strength, 00:04:27.000 --> 00:04:29.000 immortality, 00:04:29.000 --> 00:04:31.000 and 00:04:31.000 --> 00:04:34.000 invisibility.