How is it that bugs take no fall damage?
In: Physics
Basically same way we don’t damage using parachutes. Some bugs have simply air friction and weight ratio that it’s like having a natural parachute at all times.
To a such bug, air is more like a liquid, so it falls through it like you would sink into a deep lake. Even if lake is super deep – like 15 stories deep, you still won’t crash the bottom of the lake in the end, water slows you down so much all the way.
Even though acceleration by gravity is same, water limits the speed you end up with (called terminal velocity) much more than air would. But if gravity was – 10 times stronger – say – on different a planet or whatever, you could totally splat to the bottom of such lake and water friction couldn’t overcome it enough to save you.
When you fall you push air around you. Feel it with your hand. The air is also pushing on you. When a bug falls, the air pushes against it too hard for it to go fast because it it so small and light. Drop a leaf and a rock, observe.
Edit: Gravity pulls on the leaf and rock equally.
Speed required to damage them is greater than maximum falling speed possible due to air friction
If you get scaled down so you’re half the height, you’re 1/4 as strong, and have 1/4 the surface area, but you’re only 1/8 as heavy. This continues the smaller you go. For a very small bug, you might have a surface area to weight ratio similar to a sheet of paper.
The bigger the thing, the more gravity affects it. So, the smaller the thing, the less gravity affects it. Human go splat, ant go plop.
Fall damage is the body being unable to keep up with the massive forces required to bring an object to a stop in a short period of time. For a human, trying to stop 100lbs within 5 feet (a **20:1** ratio for my example human) gets tough pretty quickly depending on how fast they are going. According to a brief google search, the average house fly weighs something like .00001lbs and is .023ft tall (a **1:2300** ratio). So the ratio is like 23,000 times better for them to start with. IE: bugs have less weight to decelerate in a relatively longer period of time (if we assume the two creatures are falling at the same speed)
However, another result of this smaller weight, is that air resistance becomes a much bigger factor when falling. A tiny little updraft can make the insect lose almost all of its downward momentum, and their terminal velocity is much slower as a result. So even though my previous paragraph assumed that the human and bug were falling at the same speed, that’s almost impossible. A bug will fall WAY slower.
Not only that, but there’s something called the Squared-Cubed law which says things like “if something doubles in height, it usually multiplies its weight by around 8” and that has further implications for our comparison. One effect of this is that while large creatures may have stronger bones compared to small ones (you don’t see us getting flattened by a fly swatter, for example), but a lot of that strength is spent simply keeping us upright in the first place to counteract the massive increase of weight our size comes with (see that ratio I posted earlier), so when something like a human is met with an impact, that force is being added on top of the strain our bodies are already under as we maintain our own shape. A bug barely has to spend any energy maintaining its own structure, so nearly all of its strength can be devoted to absorbing the impact properly.
So yeah, with all of that combined, comparing the amount of damage a human takes from a fall vs an insect, any damage the bug takes would be basically nonexistant compared to what us humans are used to.
The terminal velocity of an object, aka the fastest a thing can fall before air resistance stops it from speeding up any more, gets bigger with weight, and smaller with cross-sectional area (you can think of cross-sectional area as just, how much of the object you can see from one direction).
This means heavy things fall faster, and wide things (like paper when its wide side is facing down, or a frisbee) fall slower.
Now, weight increases according to how big a thing is, and so does area **but** they increase a different speeds.
Imagine you have a single cube. Now imagine growing that cube so each edge is twice as long as the original.
To fill this new, bigger cube, it takes *8 of the original cube* (2 cubes along each edge). This makes the cube *8 times as heavy*.
On the other hand, each side of the cube only takes 4 of the original cube’s sides to make. This means the cube’s *cross-sectional area 4 times as big* as the original.
From those examples, you see that increasing something’s size increases its weight faster than its cross-sectional area.
This holds in reverse too. Shrinking something shrinks its weight faster than its area.
Now, remember that bigger area means slower fall, and bigger weight means faster fall.
If you take a human, who falls fast enough to hurt a lot, and shrink them down to the size of a bug, their weight will shrink a lot more than their area, so in turn, they’re going to fall a lot slower than a normal human.
This is most of the reason that bugs “don’t take fall damage”, as you said.
Smaller things are stronger relative to their size.
Some effects and forces dominate at different size scales. Like how an ant can carry 10-50 times their body weight. And grasshoppers can jump so far compared to their size. And why bugs find water to be very gloopy.
Suppose that a thing has length ***L***. It then has area ***L******^(2,)*** ***and volume L******^(3)***. Now imagine increasing L and see what happens to each. Area increases more than length, and volume increases even faster. Some effects may depend upon area, some on volume, and so the relative strength of these changes at different size scales.
The mass and weight will scale with it’s volume. But the strength the material it’s made of will scale with area (think of the thickness of an iron rod). So bugs are very tough and strong for their weight.
Also, the air resistance they feel scales with area, so they will fall slower and fly easier.
They aren’t very dense so they don’t hit the ground very hard. In scientific terms, their low terminal velocity and lack of mass mean there is not much force on them when they hit the ground.
There’s a very useful thought tool called “squares versus cubes”. The idea is that if one property is proportional to the square of something, and another property is related to the cube of something, you can pretty much ignore everything else.
In this case, the mass an object (an insect, in this case, but the same applies to all objects) is roughly proportional to the cube of its length, because stuff on the inside has mass. And the drag that an object experiences is roughly proportional to the square of its length, since it’s only the leading surface that has to push through air.
So the bigger a thing gets, the less drag matters, and conversely, the smaller a thing gets, the more drag matters. Bugs, being very small, are greatly slowed by the air they’re falling through because the ratio of their mass (which gravity pulls against) to their area (which wind pushes against) is small.
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