What Happens If We Throw an Elephant From a Skyscraper? - In A Nutshell

 Let's start this video by throwing amouse, a dog, and an elephant from a skyscraper onto something soft. Let's say, a stack of mattresses. The mouse lands and is stunned for a moment, before it shakes itself off, and walks away pretty annoyed, because that's a very rude thing to do. The dog breaks all of its bones and dies in an unspectacular way, and the elephant explodes into a red puddle of bones and insides and has no chance tobe annoyed. Why does the mouse survive, but the elephant and dog don't? The answer is size. Size is the most underappreciated regulator of living things. Size determines everything about our biology, how we are built, how weexperience the world, how we live and die. It does so because the physical laws aredifferent for different sized animals. Life spans seven orders of magnitude,from invisible bacteria to mites, ants, mice, dogs, humans, elephants and, bluewhales. Every size lives in its own unique universe right next to each other,each with its own rules, upsides, and downsides. 

We'll explore these differentworlds in a series of videos. Let's get back to the initial question: Why did ourmouse survive the fall? Because of how scaling size changes everything; a principle that we'll meet over and over again. Very small things, for example,are practically immune to falling from great heights because the smaller youare the less you care about the effect of gravity.Imagine a theoretical spherical animal the size of a marble. It has threefeatures: its length, its surface area, (which is covered in skin) and its volume,or all the stuff inside it like organs, muscles, hopes and dreams. If we make itten times longer, say the size of a basketball, the rest of its featuresdon't just grow ten times. Its skin will grow 100 times and it's inside (so it'svolume) grows by 1000 times. The volume determines the weight, or more accurately,mass of the animal. The more mass you have, the higher your kinetic energybefore you hit the ground and the stronger the impact shock. The moresurface area in relation to your volume or mass you have, the more the impactgets distributed and softened, and also the more air resistance will slow youdown. An elephant is so big that it has extremely little surface area in ratioto its volume. So a lot of kinetic energy gets distributed over a small space andthe air doesn't slow it down much at all. That's why it's completely destroyed inan impressive explosion of goo when it hits the ground. The other extreme,insects, have a huge surface area in relation to their tiny mass so you canliterally throw an ant from an airplane and it will not be seriously harmed. Butwhile falling is irrelevant in the small world there are other forces for theharmless for us but extremely dangerous for small beings. Like surface tensionwhich turns water into a potentially deadly substance for insects. How does itwork? Water has the tendency to stick to itself; its molecules are attracted toeach other through a force called cohesion which creates a tension on itssurface that you can imagine as a sort of invisible skin. For us this skin is soweak that we don't even notice it normally. 

If you get wet about 800 gramsof water or about one percent of your body weight sticks to you. A wet mousehas about 3 grams of water sticking to it, which is more than 10% of its bodyweight. Imagine having eight full water bottle sticking to you when you leavethe shower. But for an insect the force of water surface tension is so strongthat getting wet is a question of life and death.If we were to shrink you to the size of an ant and you touch water it would belike you were reaching into glue. It would quickly engulf you, its surfacetension too hard for you to break and you'd drown. So insects evolved to be waterrepellent. For one their exoskeleton is covered with a thin layer of wax justlike a car. This makes their surface at least partly water repellent because itcan't stick to it very well. Many insects are also covered with tiny hairs thatserve as a barrier. They vastly increase their surface area and prevent thedroplets from touching their exoskeleton and make it easier to get rid ofdroplets. To make use of surface tension evolution cracked nanotechnologybillions of years before us. Some insects have evolved a surface covered by ashort and extremely dense coat of water repelling hair. Some have more than amillion hairs per square millimeter when the insect dives under water air staysinside their fur and forms a coat of air. Water can't enter it because their hairs aretoo tiny to break its surface tension. But it gets even better, as the oxygen ofthe air bubble runs out, new oxygen diffuses into the bubble from the wateraround, it while the carbon dioxide diffuses outwards into the water. And sothe insect carries its own outside lung around and can basically breatheunderwater thanks to surface tension. This is the same principle that enablespond skaters to walk on water by the way, tiny anti-water hairs. The smaller you getthe weirder the environment becomes. 

At some point even air becomes more andmore solid. Let's now zoom down to the smallest insects known, about half the sizeof a grain of salt, only 0.15 millimeters long: the Fairy Fly.They live in a world even weirder than another insects. For them air itselfis like thin jello, a syrup-like mass surrounding them at all times.Movement through it is not easy. Flying on this level is not like elegantgliding; they have to kind of grab and hold onto air. So their wings look likebig hairy arms rather than proper insect wings.