If humans could fly, without tools and machines, how fast do you think we would go? As of 2012, the world record for fastest short-distance sprint speed is roughly 27 miles per hour. Running speed depends on how much force is exerted by the runner's legs, and according to Newton's Second Law of Motion, force is the product of mass times acceleration. And Newton's Third Law states that for every action, there is an equal and opposite reaction. So, that means running requires having a ground to push off from, and the ground pushes back against the runner's foot. So, flying would actually be more similar to swimming. Michael Phelps is currently the fastest human in water and the most decorated Olympian of all time. Guess how fast he swims? The answer may surprise you. His fastest recorded speed is less than 5 miles per hour. A child on the ground can easily outrun Michael Phelps in water, but why is that? Well, let's go back to Newton's Third Law of Motion. When we run, we move forward by pushing against the ground with our feet and the ground pushes back, propelling us forward. The ground is solid. By definition, it means the particles are essentially locked into place and must push back instead of getting out of the way, but water is liquid and flows easily. When we move our limbs to push back against the water, a part of the water molecules can just slide past one another instead of pushing back. Now, let's think about flying. Air has a lot more free space for particles to move past one another, so even more of our energy would be wasted. We would need to push a lot of air backwards in order to move forward. Astronauts move around in shuttles in zero gravity when they're in outer space by pulling on handles installed on the ceiling walls and floors of the shuttle. Now, imagine you were given the ability to float. How would you move around in the middle of the street? Well, you wouldn't get very far by swimming in air, would you? Nah, I don't think so! Now, assuming you were granted the ability to float and the speed to move around efficiently, let's discuss the height of your flight. According to the Ideal Gas Law, P-V N-R-T, pressure and temperature has a positive correlation, meaning they increase and decrease together. This is because the air expands in volume with less pressure, so the molecules have more room to wander around without colliding into each other and creating heat. Since the atmospheric pressure is a lot lower in high altitudes, it would be freezing cold if you were flying above the clouds. You'd need to wrap yourself up to keep your core body temperature above 95 degrees Fahrenheit, otherwise you'd start shivering violently, gradually becoming mentally confused and eventually drop out of the sky due to loss of muscle control from hypothermia! Now, the Ideal Gas Law implies that as the pressure decreases, gas volume increases. So, if you were to fly straight up too quickly, the inert gas in your body would rapidly expand the way soda fizzes up when shaken. The phenomenon is called "the bends," decompression sickness, or "divers disease" since deep sea scuba divers experience this when they come up too quickly. This results in pain, paralysis, or death, depending on how foamy your blood becomes. Okay, well, let's say you want to fly just a few meters above the ground where you can still see the road signs and breath oxygen with ease. You'll still need goggles and a helmet to protect you from birds, insects, street signs, electrical wires, and other flying humans, including flying cops ready to hand you a ticket if you don't follow the flying rules, buddy. Now remember, if you have a collision mid-air that knocks you unconscious, you would experience free fall until you hit the ground. Without society or the laws of physics, flying would be a totally awesome ability to have. But, even if we could all just float around a few feet above the ground and only moving at a snail's pace, I'm telling you, it's still a cool ability that I'd want, wouldn't you? Yeah, I thought so. Now, which superpower physics lesson will you explore next? Shifting body size and content, super speed, flight, super strength, immortality, and invisibility.
Kada bi ljudi mogli da lete bez alata i mašina, šta mislite, koliko brzo bismo išli? Od 2012, svetski rekord za najveću brzinu trčanja na kratkoj udaljenosti je oko 43 kilometra na čas. Brzina trčanja zavisi od toga koliko sile ispoljavaju noge onoga ko trči, i po Njutnovom drugom zakonu kretanja, sila je proizvod mase puta ubrzanja. A Njutnov treći zakon kaže da za svaku akciju postoji jednaka i suprotna reakcija. To znači da je za trčanje potrebno tlo da se od njega odguramo i tlo se odupire od stopala onoga ko trči. Letenje bi zapravo bilo sličnije plivanju. Majkl Felps je trenutno najbrži čovek u vodi i Olimpijac sa najviše odlikovanja u istoriji. Pogodite koliko brzo pliva? Odgovor će vas možda iznenaditi. Najveća zabeležena brzina je manja od 8 kilometara na čas. Dete na površini lako može da bude brže od Majkla Felpsa u vodi, ali zašto je to tako? Pa, vratimo se Njutnovom trećem zakonu kretanja. Kada trčimo, krećemo se unapred tako što se odupiremo od zemlje svojim stopalima a zemlja se odupire nazad i gura nas unapred. Zemlja je čvrsta. Po definiciji, to znači da su čestice zapravo fiksirane u prostoru i moraju da guraju nazad umesto da se sklone, ali voda je tečna i lako teče. Kada pomeramo svoje udove da se odgurnemo od vode, deo molekula vode može samo da proklizne jedan pored drugog umesto da guraju nazad. Razmislimo sada o letenju. Vazduh ima puno više slobodnog prostora gde čestice mogu da se kreću jedna pored druge, tako da bi se protraćilo još više naše energije. Morali bismo da guramo mnogo vazduha nazad kako bismo se kretali unapred. Astronauti se kreću u šatlovima u nultoj gravitaciju kada su u svemiru tako što vuku ručke na zidovima plafona i podovima šatla. Sada zamislite da imate mogućnost lebdenja. Kako biste se kretali nasred ulice? Pa, ne biste se puno odmakli plivajući u vazduhu, zar ne? Ni ja ne mislim tako! Recimo da vam je data mogućnost lebdenja i brzina da se efikasno krećete, popričajmo o visini vašeg letenja. Po Zakonu idealnog gasa, P-V N R-T, pritisak i temperatura su u pozitivnoj korelaciji, što znači da se zajedno povećavaju i smanjuju. Ovo se dešava zato što se vazduh širi u zapremini sa manje pritiska, tako da molekuli imaju više prostora da lutaju a da se međusobno ne sudare i stvore toplotu. Pošto je atmosferski pritisak mnogo niži na velikim visinama, bilo bi neverovatno hladno kada biste leteli iznad oblaka. Morali biste da se zamotate kako biste održali temperaturu tela iznad 35 stepeni Celzijusa, ili biste počeli snažno da drhtite i postepeno postajete mentalno zbunjeni i na kraju biste pali s neba zbog gubitka kontrole mišića od hipotermije! Zakon idealnog gasa navodi da kako se smanjuje pritisak, tako raste zapremina gasa. Kada biste leteli pravo previše brzo, inertni gas u vašem telu bi se naglo raširio kao što se gazirano piće zapeni kada ga protresete. Ova pojava se zove aeroembolizam, dekompresiona bolest ili "bolest ronilaca", pošto ronioci na velike dubine ovo iskuse kada prebrzo izađu na površinu. Ovo za posledicu ima bol, paralizu ili smrt, u zavisnosti od toga koliko se zapeni vaša krv. U redu, recimo da želite da letite samo nekoliko metara nad zemljom gde još uvek možete videti putokaze i disati vazduh s lakoćom. Još uvek će vam biti potrebni naočare i kaciga da se zaštitite od ptica, insekata, uličnih znakova, električnih dalekovoda i drugih ljudi koji lete, uključujući i leteće policajce koji su spremni da napišu kaznu ako ne pratite pravila letenja, druškane. Zapamtite, ako usred vazduha imate sudar od kog se onesvestite, iskusili biste slobodan pad dok ne biste udarili tlo. Bez društva ili zakona fizike, letenje bi bilo sjajna sposobnost. Ali čak i kada bismo mogli samo da lebdimo nekoliko metara nad zemljom i krećemo se brzinom puža, kažem vam, opet je to super sposobnost koju bih želeo da imam, a vi? Tako sam i mislio. Sada, koju ćete lekciju o supermoćima iz fizike istražiti nakon ove? Menjanje veličine i sadržaja tela, superbrzina, letenje, nadljudska snaga, besmrtnost ili nevidljivost.