clairostan t1_jef4uof wrote
Reply to comment by Any_Branch_4379 in ELI5: why can’t someone who is light in weight punch as hard as someone who is heavier? by Any_Branch_4379
inertia plays a factor more so in how well someone can take a punch. inertia is resistance to change in velocity. that change in velocity in your face when you get punched dictates how hard your brain shakes inside your skull, which determines how hurt you get (and whether you go unconscious or not). if you're a bigger person with a bigger head, stronger neck muscles, denser skeleton, stronger base, etc, you'll be able to absorb a punch better than someone who is smaller because you can resist the change in velocity better than a smaller person can. it's why combat athletes fight people who are the same weight as them. keeps it fair (on top of the obvious fact that same size people can generate similar levels of force)
Keeper151 t1_jefe5z7 wrote
In addition, that inertia isn't always a good thing on part of the person getting hit.
An often overlooked factor in how damaged you get is the amount of force it takes to overcome inertia. Hit a smaller person in the body, they go flying without breaking ribs because the amount of force necessary to knock them over is less than what's required to break ribs. Hit a bigger person, and their body has to soak more impact before movement occurs. Depending on the size difference and the amount of tissue padding the larger person has, there is a wide range of potential outcomes.
This combines unfavorably with the kinetic force equation, as velocity has more effect on force than mass. Smaller object moving faster = more penetration, which is bad for the person getting hit. It's far more likely to break ribs/jaws/orbitals/teeth as the smaller bits will fail before inertia is overcome.
Training helps with this, as you learn when to strike for maximum effect. It's counterintuitive due to the desire to avoid pain, but it's best to hit someone that is coming straight at you (who is usually swinging for your face) because you're adding their mass & velocity to your own. Hitting someone that's retreating reduces the force of your strikes. Think of the difference between a head-on collision and getting rear ended by someone going 50 when you're going 35.
For example: putting strong kicks into someone my size is usually less useful than putting them into someone larger than me. I have to time my kick so the person my size is advancing into the strike, giving me more force to overcome (and therefore more force I can put into them before they start changing direction) which directly translates into damage inflicted. With a larger opponent, I can deliver a full-force kick to the abdomen and they will fold like an omlette before they go flying because all the energy of my kick went straight into their body instead of getting wasted.
Senrabekim t1_jegw5wx wrote
There's a really good example of the inertia thing you're talking about. Paquiao Vs Marquez 4 iirc where Paq gets knocked out. He's stepping into Marquez and moving directly into Marquez' hook and just gets obliterated. That hit was always going to be huge, but adding in Paquiao's own momentum is huge.
Keeper151 t1_jegxmsb wrote
That's a perfect example, thank you.
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