A human falling down from three times their own height (six metres or so) would be horribly injured, while bugs seem to just walk on. How does this work? Shouldn’t they be falling at a similar speed, due to gravity?
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It’s because of terminal velocity, that is the point where acceleration from gravity balances out with resistance from wind. The average terminal velocity for an insect is about 2m/s, the terminal velocity for a human is about 60m/s. If both you and an insect jumped from the Empire State Building at the same time you’d reach earth a lot faster than the insect would, but if the experiment happened in a vacuum you’d be able to lock eyes with the insect and would both hit the ground at the same time and at the same speed… a blistering 86m/s or 192mph
Additionally things are just relatively stronger the smaller they are. Ants can lift 50 times their body weight, with minimal training an average child can dead hang for 2 minutes something adults struggle with, elephants can’t jump.
2 things:
1: Terminal velocity(aka the maxspeed at which you can fall outside of a vaccum), is based on your overall weight vs your overall surface area: for a human sized creature this is a known value while for an ant sized creature this is much lower.
2: Exoskeletons are neat at resisting impacts compared ot endoskeletons that have ot face the stresses of supporting themselves aswell as the impact.
> Shouldn’t they be falling at a similar speed, due to gravity?
Nope! And even if they were, it wouldn’t hurt them as much.
When you fall, two forces act on you: gravity and air resistance. Gravity is ~constant for our purposes, but air resistance rises as you speed up. At some speed, called *terminal velocity*, the two balance out, where air resistance is slowing you down as much as gravity is speeding you up. For a typical human skydiving, this speed is about 100 m/s (~223 mph), which is more than fast enough to kill you on impact if you don’t have a parachute or other way to slow down.
The more area you present as you fall (that is, the more cross-sectional area you have at a right angle to your movement), the more air resistance drags on you: it’s proportional to the area, or to length^(2). But your weight, and thus the force of gravity, is proportional to your *volume*, or to length^(3). As a result, **gravity grows faster than air resistance for a larger object of the same basic shape and density**, meaning that larger objects have higher terminal velocities. Specifically, with all other factors held equal, terminal velocity rises with the square root of length.
A golf ball, for example, has a terminal velocity of around 30 m/s, much slower than a human. It isn’t as much lower as that formula would suggest because golf balls are smoother, which also affects air resistance, but it’s still much lower.
An ant, which is much smaller still, has a terminal velocity of only about 2 m/s. That’s only a bit above walking speed; even for a human that would be a more than survivable impact. You could drop an ant from space (not from orbit) and they wouldn’t die from the impact.*
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But there’s another factor here, too: the [square-cube law](https://en.wikipedia.org/wiki/Square%E2%80%93cube_law) (which we saw in another form in the previous section).
A material’s strength is defined in terms of the maximum pressure (force per area) it can take. Thus, the amount of force a beam can take is proportional to its area, that is, to its length^(2).
But the mass of an object is proportional, as above, to its length^(3). And since the force of an impact is proportional to that mass, **the strength required for a material to support itself rises the bigger the object is**.
Imagine, say, building a house out of toothpicks. It’s pretty easy to build a tiny house with them! It can be quite stable with only marshmallows for structural support. That’s because the tiny house, which is perhaps ~50x smaller in terms of lengths than a real house, needs ~50x less structural strength, and most materials are that strong. Try to build an *actual* house out of toothpicks, though, and it won’t work.
So when our ant strikes the ground at 2 m/s, they *also* benefit from the fact that – as an object ~1000x shorter than a human, give or take – their body effectively has ~1000x the structural strength that yours does. This isn’t because they’re actually stronger, it’s just a consequence of their size. If you were that small, you could lift objects many times your size, too.
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The combination of these two effects means that ants and other small creatures are pretty much totally undamaged by falls. You need to get up to the size of, say, a medium-size bird or mammal for falls to start posing a serious risk of death.
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* You might wonder why meteors manage to hit the ground so hard. The answer is that they’re going so fast that even though the atmosphere is slowing them down, it doesn’t have time to slow them down to terminal velocity, so they impact at a high speed if they survive to land at all.
I would like to add to all the comments about air resistance and terminal velocity, that the building bricks of biological structure has a similar material strength, but need to support a negligible weight ratio.
2 things:
1: Terminal velocity(aka the maxspeed at which you can fall outside of a vaccum), is based on your overall weight vs your overall surface area: for a human sized creature this is a known value while for an ant sized creature this is much lower.
2: Exoskeletons are neat at resisting impacts compared ot endoskeletons that have ot face the stresses of supporting themselves aswell as the impact.
I would like to add to all the comments about air resistance and terminal velocity, that the building bricks of biological structure has a similar material strength, but need to support a negligible weight ratio.
Insects are built to jump and safely land at much greater distances relative to their size than humans are. They have multiple limbs to absorb the impact and are tiny…so far less effected by gravity to begin with. Plus they have exoskeletons to protect their insides from damage.
Insects are built to jump and safely land at much greater distances relative to their size than humans are. They have multiple limbs to absorb the impact and are tiny…so far less effected by gravity to begin with. Plus they have exoskeletons to protect their insides from damage.
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