How does an ant survive a fall from a great height but another creature dies in a fall from a height of same scale ?
In: Biology
It’s because of something called the the square-cube law. There’s a famous quote:
> “You can drop a mouse down a thousand-yard mine shaft and, on arriving at the bottom, it gets a slight shock and walks away. A rat is killed, a man is broken, a horse splashes.” — J.B.S. Haldane
https://www.physicsforums.com/threads/a-man-is-broken-a-horse-splashes.585757/
https://en.wikipedia.org/wiki/Square%E2%80%93cube_law
tl;dr: as things get bigger, surface area and volume increase at different rates. A creature that is 30% bigger than another may way three times as much. This has a ton of physical implications.
Kurzgesagt did a [wonderful video](https://youtu.be/f7KSfjv4Oq0) on size a while back you might enjoy!
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Less mass means less impact upon falling. Therefore, bugs are fine with falling from great heights. I also think air pressure is involved, though I’m not sure how.
When something is in freefall, there are essentially 2 opposite forces acting upon the object: the pull of gravity and air drag. Gravity pull is constant but air drag increases as “surface” increases but also as the falling object’s speed increases. There are two stages in freefall: first gravity is stronger than air drag and your falling speed keeps increasing, as your speed increases air drag increases and you eventually reach a second stage where air drag becomes as strong as gravity. At this point the falling speed cannot increase anymore, the object has reached its terminal velocity.
Ants and insects alike have very low terminal velocities because they have a large “surface” compared to their very low mass. As such the deceleration they experience when hitting the floor is not strong enough to damage them.
Elephants have a huge mass compared to their “surface” so their terminal velocity is much higher. Incidentally, the deceleration induced from hitting the floor induces huge forces that are enough to crush its bones, muscles and organs.
Why does a feather fall slowly, but a brick fall fast? It is because the air slows down the feather more. Why does a brick break glass, but a feather doesn’t? Because the force applied by the brick is much greater than from the feather.
The same thing applies to ants. The ant is very light, so gravity doesn’t provide much force to push it through the air. In addition, because it is so light, there isn’t much force happening when it hits the ground.
Scientifically, we talk about the ‘square cube law’. Things like how fast they fall, how strong they are etc are based on areas, and areas are calculated by squaring its measurements – like length × width. But its weight comes from its volume, which comes from cubing its measurements – length × width x height. So as something gets bigger, its weight increases much faster than its wind resistance or strength. So tiny things fall slow, are strong and hit light, heavy things fall fast, are relatively weak, and hit hard.
Let’s first agree on the fact that the faster you fall, the harder it will be to gain speed, because the earth’s gravity will have to pull you through more and more air.
Because earth’s gravity is practically constant, at some point you’ll reach the equilibrium where you can’t be pulled faster downwards because the air is breaking your fall. This is called your terminal velocity.
Now, because an ant is so light, even though it is small, its terminal velocity will be low enough that the ant won’t be harmed, the air has an easier time breaking something light, and an ant happens to be light enough.
You might want to read JBS Haldane’s classic essay “[On Being the Right Size](http://www.phys.ufl.edu/courses/phy3221/spring10/HaldaneRightSize.pdf)”
He writes about gravity:
>To the mouse and any smaller animal it presents practically no
dangers. You can drop a mouse down a thousand-yard mine shaft; and, on arriving at the bottom it gets a slight shock and walks away, provided that the ground is fairly soft. A rat is killed, a man is broken, a horse splashes. For the resistance presented to movement by the air is proportional to the surface of the moving object. Divide an animal’s length, breadth, and height each by ten; its weight is reduced to a thousandth, but its surface only a
hundredth. So the resistance to falling in the case of the small animal is relatively ten times greater than the driving force.
As animals get smaller, they have a higher and higher surface area relative to their mass, so they fall more slowly. There are a number of other side-effects that depend on size, which are discussed in the article.
The answer is that ants have a relatively small terminal velocity compared to their size. Terminal velocity is the speed where the force due to gravity balances out with air resistance, and is the highest speed you can achieve while falling through air. Since insects are very light and have a relatively high surface area to mass ratio, the fastest they can fall is pretty slow. And because they’re so light, the impact force from the ground (remember the landing is what kills you, not the fall) is also smaller. It would be like a person falling from a huge height, but wearing a parachute and weighing half of what they normally do.
Because “scale” doesn’t address the ultimate impact velocity. Something falling from a greater height lands with a greater velocity. Compare yourself lying flat and falling about a foot (your “height”) vs. standing up and falling 6 feet. Which is going to result in the greatest impact force?
That acceleration is a quadratic equation is overlooked by a lot of people.
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