I recall seeing one of these years ago but never since. I have no idea of what this thing would be called: basically it was a punching bag that had a sensor in it to let you know how hard you punched/kicked it.
So, first, does anyone make these? If not, it’s probably too hard for me to make one on my own, right?
It’s called a “sparring partner.”
Chances are likely that the bag isn’t going to give any valid data back–if you hit really, really hard, hard enough to make a Buick move, but it’s a really slow punch, it’s not a good one. Also, if you hit really, really fast, but very light, it’d show up as a poor punch, but if your target was somebody’s nose, or eye, or groin…
There was one I remember called the “Slam Man” that was vaguely person shaped and had lights that would supposedly light up when you hit it properly. Reviews and talk about it were that it was gimmicky junk that broke pretty easily.
Well, since force is mass*velocity, and the mass of your hand is unchanged, speed is really what makes a punch hard or soft, aside, from pulling it at the last moment. So you can’t really hit someone fast, but light, assuming you follow through.
Unless you’re playing Street Fighter 2. But that doesn’t count.
You aren’t talking about force, you are talking about impulse. Thus you have the further parameter of duration of impact.
^^ What he said.
Those target-sensor things exist and tend to run expensive. I asked around some:
Shotokan karate instructor (6th dan): Don’t worry about how hard you’re hitting, worry about how well you’re hitting.
TKD/Hapkido instructor: (8th dan/5th dan, respectively): Overpriced fun, more or less useless.
TKD Instructor (4th dan): That’s an ego boost. Stop looking for that and train for real.
I agree with most of that. I recall seeing people rig something like that up on a kids science TV show once, but other than that, I’m clueless.
Agree with the above, but have to say I like the OP’s title, very zen 
“Stand under a water fall for 10 minutes chanting Cecil is great and the thing which may or may not exist shall be found.”
Nitpick: Momentum if massvelocity. Force is equal to massacceleration.
Bwah! Reminds me of a story I saw on the BBC website some time ago - some brouhaha about someone who worked for the Queen or something. A publicist was saying that they can’t say whether or not something that may have happened happened, or something of that sort… “I’m not going to comment on an incident that I can’t describe, which may or may not have happened.”
I’m pretty sure these things exist. Saw it in a Rocky movie once.
And movies don’t lie. 
Find octuplets and a decibel meter.
Punch one, read meter.
Punch the next, read meter.
When the meter is at its loudest, use that punching style.
It’s scientific.
Not that I don’t appreciate you asking, but I really, really dislike snippy instructors(I suppose it’s only the third guy though). I don’t know how the question was phrased to him, but I take issue with him assuming that me looking for potentially useful feedback = slacker looking for feelgood gratification where I don’t have to do anything demanding.
Re: sparring. Whiplash has put me out for close to six months now. Class 2x a week and extracirrucular training is all I can take. I can grapple fine - tapping out of a neck crank before it gets started is a lot easier than taking head shots.
I apologize on his behalf. He is somewhat snippy sometimes (and very hardcore traditional). Actually - all the time. I mostly, to be honest, used your question as an excuse to call the gym where I trained before leaving for college and catch up with my buddies there.
Regrettably, even though I’m going to be home for Thanksgiving, I’m not going to be able to work out there, due to a very incovienant ankle injury…stupid rocks…
There’s certainly no need to for you to apologize. I think I overreacted (cranky, have a cold and haven’t been sleeping well lately) and should apologize for that. I do appreciate you asking around.
The first response you got was very interesting - after all, that’s where the “art” part of MA comes in.
I remember seeing one of these in an episode of CSI. IIRC, they used it to measure the difference in force between a (supposedly) equal punch in a “straight-laced” glove versus a glove laced with mercury to determine that a boxer had put mercury in his gloves and thusly killed an opponent in the ring (that is, some property of the mercury caused the glove to strike with substantially more force, enough so that in this case the poor dude who got socked died).
Anyway, unless you’re investigating a boxing crime, it sounds like an ego boost to me. Or just an interesting gadget to play with.