Why does a flying insect not die when you slap it in mid air ? The slap should have the same impact as being hit by a bus .
In: Physics
Most of the time you just push it out of the way with the wind your hand displaces. If you do hit it it would depend on many factors. The Point of impact, the Velocity , and so on.
Your hand moves the air in front of it while it’s moving, so before they feel your hand, they’re already being pushed fairly hard by the wind you’re generating. This moves them in the same direction and lessens the force of the impact.
They also have very short neural connections and begin reacting in a split second to move away.
They’re also wearing helmets all the time.
Combined, they’re pretty durable against midair swats – although you can definitely injure or kill them this way, particularly larger ones that crumple more easily. Exoskeleton strength doesn’t scale well.
Flies, and lots of insects in general, are extremely light, so forces of impact don’t affect them as much because they basically just bounce off whatever it is that hits them.
For comparison, a human, which is much heavier, isn’t just crushed because of the bus, but is partly crushed because of the weight of the stationary part of the body resisting and pushing against the part being pushed aside by the bus.
Smaller, lighter animals can handle acceleration much better than larger animals. The bodies of larger animals have a large amount of inertia, which causes their tissues to get all scrambled (damaged) when the body is accelerated/decelerated.
You might be interested in this old essay by biologist J.B.S Haldane, “On Being the Right Size” https://www.phys.ufl.edu/courses/phy3221/spring10/HaldaneRightSize.pdf
Then what is the impact of it being hit by a bus?
Because being hit by a bus does seem to kill most insects.
Physics says force is equal to mass multiplied by acceleration. The mass of an insect is very low and the area of your hand it impacts is also pretty low, so it’s unlikely all of the force of your swing is going into the insect. Most of that force is just going into swinging your arm around and pushing the air around. Your hand is also made of relatively flexible stuff, so some of the force goes into deforming the soft tissue of the hand hitting the insect. Compare that to the bus and the person being hit by it, and the amounts of mass are much larger. The area of person being impacted by the area of bus are much larger as well, so more force can be transferred from the bus to the person.
You hand is not a bus. It doesn’t have the mass or speed and certainly not the combined force of the bus.
People assume that these things scale perfectly, that is because you hand is as large as a bug compared to a fly as a bug is to you that the impact would be the same, but that isn’t how physics works at all and they are completely different. Things don’t scale like that. It’s why there a size limit to how small a warmblooded animal can be and to how large an animal can be before it crushes itself to death, because the physics simply do not scale.
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