Some superheros can move faster than the wind. The men in Apollo 10 reached a record-breaking speed of around 25,000 miles per hour when the shuttle re-entered the Earth's atmosphere in 1969. Wouldn't we save a lot of time to be able to move that fast? But what's the catch? Air is not empty. Elements like oxygen and nitrogen, even countless dust particles, make up the air around us. When we move past these things in the air, we're rubbing against them and creating a lot of friction, which results in heat. Just like rubbing your hands together warms them up or rubbing two sticks together makes fire, the faster objects rub together, the more heat is generated. So, if we're running at 25,000 miles per hour, the heat from friction would burn our faces off. Even if we somehow withstood the heat, the sand and dirt in the air would still scrape us up with millions of tiny cuts all happening at the same time. Ever seen the front bumper or grill of a truck? What do you think all the birds and bugs would do to your open eyes or exposed skin? Okay, so you'll wear a mask to avoid destroying your face. But what about people in buildings between you and your destination? It takes us approximately one-fifth of a second to react to what we see. By the time we see what is ahead of us and react to it - time times velocity equals distance equals one-fifth of a second times 25,000 miles per hour equals 1.4 miles - we would have gone past it or through it by over a mile. We're either going to kill ourselves by crashing into the nearest wall at super speed or, worse, if we're indestructible, we've essentially turned our bodies into missiles that destroy everything in our path. So, long distance travel at 25,000 miles per hour would leave us burning up, covered in bugs, and leaves no time to react. What about short bursts to a location we can see with no obstacles in between? Okay, let's say a bullet is about to hit a beautiful damsel in distress. So, our hero swoops in at super speed, grabs her, and carries her to safety. That sounds very romantic, but, in reality, that girl will probably suffer more damage from the hero than the bullet if he moved her at super speed. Newton's First Law of Motion deals with inertia, which is the resistance to a change in its state of motion. So, an object will continue moving or staying at the same place unless something changes it. Acceleration is the rate the velocity changes over time. When the girl at rest, velocity equals zero miles per hour, begins accelerating to reach the speed within seconds, velocity increases rapidly to 25,000 miles per hour, her brain would crash into the side of her skull. And, when she stops suddenly, velocity decreases rapidly back to zero miles per hour, her brain would crash into the other side of her skull, turning her brain into mush. The brain is too fragile to handle the sudden movement. So is every part of her body, for that matter. Remember, it's not the speed that causes the damage because the astronauts survived Apollo 10, it's the acceleration or sudden stop that causes our internal organs to crash into the front of our bodies the way we move forward in a bus when the driver slams on the brakes. What the hero did to the girl is mathematically the same as running her over with a space shuttle at maximum speed. She probably died instantly at the point of impact. He's going to owe this poor girl's family an apology and a big fat compensation check. Oh, and possibly face jail time. Doctors have to carry liability insurance just in case they make a mistake and hurt their patients. I wonder how much superhero insurance policy would cost. Now, which superpower physics lesson will you explore next? Shifting body size and content, super speed, flight, super strength, immortality, and invisibility.
Neki superheroji mogu da se kreću brže od vetra. Ljudi u Apolu 10 dostigli su rekordnu brzinu od oko 40 000 kilometara na čas kada se šatl vratio u Zemljinu atmosferu 1969. Zar ne bismo uštedeli puno vremena kada bismo mogli da se krećemo tako brzo? Ali u čemu je caka? Vazduh nije prazan. Elementi poput kiseonika i azota, čak i bezbrojne čestice prašine, čine vazduh oko nas. Kada se krećemo pored ovih stvari u vazduhu, mi ih dodirujemo i stvaramo dosta trenja, što za posledicu ima toplotu. Isto kao što zagrejete vaše dlanove kada ih trljate jedan o drugi ili kada trljanje dva štapa stvori vatru, što brže se predmeti trljaju, to se stvara više toplote. Ako bismo onda trčali brzinom od 40 000 kilometara na sat, toplota od trenja bi nam istopila lice. Čak i kada bismo nekako izdržali toplotu, pesak i prašina u vazduhu bi nam opet naneli milione sićušnih posekotina u isto vreme. Da li ste ikada videli prednji branik ili rešetku od hladnjaka na kamionu? Šta mislite, šta bi uradile sve ptice i insekti vašim otvorenim očima ili izloženoj koži? U redu, nosićete masku da izbegnete uništenje lica. Ali šta je sa ljudima u zgradama između vas i vašeg odredišta? Potrebna nam je otprilike petina sekunde da reagujemo na ono što vidimo. Do onog trenutka kad vidimo šta je ispred i na to reagujemo - vreme X brzina = udaljenost = jednoj petini sekunde X 40 000 kilometara na čas = 2,2 kilometra - prošli bismo to ili kroz to, za preko kilometar. Ili ćemo se ubiti tako što ćemo proći kroz najbliži zid pri nadljudskoj brzini, ili još gore, ako smo neuništivi, zapravo smo svoja tela pretvorili u rakete koje uništavaju sve ispred sebe. Tako bismo od dužih putovanja pri 40 000 kilometara na čas potpuno izgoreli, bili bismo prekriveni insektima i ne bismo imali vremena za reagovanje. A šta sa kratkim trkovima do nekog mesta gde ne vidimo nijednu prepreku? Recimo da će metak pogoditi predivnu damu u nevolji. Naš heroj uleće pri nadljudskoj brzini, hvata je i nosi na bezbedno. To zvuči veoma romantično, ali bi ta dama zapravo verovatno istrpela više štete od heroja nego od metka kada bi je pomerio pri nadljudskoj brzini. Njutnov prvi zakon kretanja tiče se inercije, što je otpor na promenu u njenom stanju kretanja. Tako će objekat nastaviti da se kreće ili će ostati na istom mestu ukoliko ga nešto ne promeni. Ubrzanje je stopa po kojoj se brzina menja tokom vremena. Kada devojka miruje, brzina je nula kilometara na čas, počinje da ubrzava da dostigne brzinu u nekoliko sekundi, brzina se naglo uvećava na 40 000 kilometara na čas, njen mozak bi udario u lobanju. A kada bi naglo stala, brzina se naglo smanjuje do nula kilometara na čas, i njen mozak bi udario u drugu stranu lobanje i pretvorio se u kašu. Mozak je suviše osetljiv da se izbori s naglim kretanjem. Uostalom, kao i svaki deo njenog tela. Zapamtite, nije brzina ta koja prouzrokuje štetu, jer su astronauti preživeli Apolo 10, već ubrzanje ili naglo zaustavljanje čine da naši unutrašnji organi udare u prednji deo naših tela kao što bismo se pomerili napred u autobusu kada vozač nagazi na kočnicu. Ono što je heroj učinio devojci je matematički isto kao da ju je pregazio svemirskim brodom pri punoj brzini. Verovatno je umrla odmah po trenutku udarca. Porodici ove jedne devojke će dugovati izvinjenje i ogroman ček za nadoknadu patnje. Da, i verovatno će ići u zatvor. Doktori moraju da imaju osiguranje od odgovornosti za slučaj da pogreše i povrede svoje pacijente. Baš se pitam koliko bi koštala polisa osiguranja za superheroje. Sada, koju ćete lekciju o supermoćima iz fizike istražiti nakon ove? Menjanje veličine i sadržaja tela, superbrzina, let, nadljudska snaga, besmrtnost, ili nevidljivost.