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<blockquote data-quote="Umbran" data-source="post: 8720981" data-attributes="member: 177">If you know enough to throw that terminology around, you also know enough to know that a &quot;pinned connection&quot; is merely an approximation.&nbsp; You can rivet steels beams together, and call that a &quot;pinned connection&quot;... until the forces are great enough to shear steel, and then those bets are off.So, to first approximation, that contact point is a pinned connection.&nbsp; It will cease to be so when the forces get high enough - but that also speaks to how this is not a simple interaction, but a complex one.You have not identified the applicable M.This is not a simple instantaneous elastic collision between two free bodies, and cannot really be approximated with one - heck, if you want to hurt someone, you need the collision to be inelastic - to deposit energy within the body, not just bounce elastically.So, you mention M, M', and M&quot;, but your equation only has M' and M&quot;.&nbsp; You do not clearly identify what object M' &quot;the mass of of body in punch&quot; is, especially when you then also refer to the &quot;total mass of the punch-er&quot; separately.FM'ad appears to have a units problem:&nbsp; F*d has units of work (so energy), but M*a has units of force, so the product FM'ad then, is not energy.Next, a is not constant in real body mechanics.&nbsp; You don't identify what the distance d is.&nbsp; Depending on what d is, we may need to talk about how the angle is not a constant either.Also, in a real application the fist continues to receive energy from the body after contact is made with the target.&nbsp; This isn't an instantaneous interaction.And finally, we note that the total kinetic energy delivered doesn't really tell us much about the punch, because exactly how that KE is delivered matters - I can deliver it so that it breaks your jaw, or I can deliver it so it gently pushes you back, and one is a hard punch and the other is not.I'm a physicist who used to teach basic mechanics to college students.&nbsp; I have noted my thoughts above.What it comes down to is that the overall mass of the puncher doesn't mean much of anything unless they are flying through the air and come to a complete stop when they hit you, which is very anime.</blockquote>

[QUOTE="Umbran, post: 8720981, member: 177"] If you know enough to throw that terminology around, you also know enough to know that a "pinned connection" is merely an approximation. You can rivet steels beams together, and call that a "pinned connection"... until the forces are great enough to shear steel, and then those bets are off. So, to first approximation, that contact point is a pinned connection. It will cease to be so when the forces get high enough - but that [I]also[/I] speaks to how this is not a simple interaction, but a complex one. You have not identified the applicable M. This is not a simple instantaneous elastic collision between two free bodies, and cannot really be approximated with one - heck, if you want to hurt someone, you need the collision to be inelastic - to deposit energy within the body, not just bounce elastically. So, you mention M, M', and M", but your equation only has M' and M". You do not clearly identify what object M' "the mass of of body in punch" is, especially when you then also refer to the "total mass of the punch-er" separately. FM'ad appears to have a units problem: F*d has units of work (so energy), but M*a has units of force, so the product FM'ad then, is [I]not energy[/I]. Next, a is not constant in real body mechanics. You don't identify what the distance d is. Depending on what d is, we may need to talk about how the angle is not a constant either. Also, in a real application the fist [I]continues to receive energy[/I] from the body after contact is made with the target. This isn't an instantaneous interaction. And finally, we note that the total kinetic energy delivered doesn't really tell us much about the punch, because [I]exactly how that KE is delivered[/I] matters - I can deliver it so that it breaks your jaw, or I can deliver it so it gently pushes you back, and one is a hard punch and the other is not. I'm a physicist who used to teach basic mechanics to college students. I have noted my thoughts above. What it comes down to is that [B]the overall mass of the puncher doesn't mean much of anything unless they are flying through the air[/B] and come to a complete stop when they hit you, which is very anime. [/QUOTE]

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