# Can E=MC2 be used when thinking about human strength

As we know just because a person has more mass that doesn't mean they can lift more weight or punch harder as those actions are more about training your technique. My story is a martial arts / superhero type and I have seen "power ratings" or rough measurements of spiritual energy like chi and chakras being used in other stories. I was wondering if E=MC2 or other equations could be used to measure a fighters potential, not their resting energy but their max capability for single or short bursts of action .

• No, $e = mc^2$ is not applicable to chemical reactions, which is what powers animal muscles. (The energy absorbed or released in chemical reactions is so small that mass is constant for all practical purposes.) As for "or other equations", this is the definition of "too broad". Dec 29, 2018 at 18:12
• @AlexP Actually, E=mc2 is applicable (it's always applicable), but you're absolutely right that it's wrong to invoke it in the OP's context since the m in the equation has noting at all to do with the person's mass, but with the (really really tiny) change in mass in the chemical reactions involved. Dec 29, 2018 at 18:18
• @MarkOlson: There's applicable and applicable. While the equation does indeed hold for chemical reactions, actually applying it to compute anything useful is quite impractical. Dec 29, 2018 at 18:25
• @AlexP: Agreed! Dec 29, 2018 at 18:30
• Only if your martial arts / superhero type can convert mass into energy as part of their fighting.This will make them effectively nuclear-powered. Considering super-strength requires more energy than can be extracted from chemical reactions involved in metabolism. If there was a mechanism to convert ting amounts of matter into a power source for superhuman fighting, and do so safely, then this could provide a hypothetical basis for a martial arts superhero. As long as they don't explode! Jan 1, 2019 at 1:16

Not really

If you know the mass of (e.g.) your arm, you can apply the equation and discover what energy would be released if the mass of that arm were converted entirely to energy. But what's the point? It has nothing to do with the force applied swinging that arm. Therefore, you have a measure that's no more valuable than simply reporting the arm's mass and yet a whole lot more confusing because no one would know what you meant.

Your arm, for example, is accelerated via muscle contraction. After that acceleration has completed, (i.e., after you know the final acceleration of the arm) you could then apply the equation for force (F = mA) to derive an energy value. The same is true for legs, head butts, etc.

Which is what people do using tools like accelerometers to measure force-of-impact. (See our sister site, Martial Arts.SE, where a question about measuring force-of-impact was posted and the answers include ways to do it from cell phones to professional equipment.)

But even this is used only as a basic measure. Arms and legs are usually still accelerating when they impact the opponent. This means you can't measure the delivered energy without tracking the acceleration of the arm moment-by-moment. Each impact would be (and will be) different based on the circumstances of the blow.

In the end, F=mA is the basis used today to do specifically what you're talking about, but the data is aquired in far more practical ways: like hitting the bag attached to a tool designed specifically to measure the impact force.

And remember that it's force, not energy, that you really want to measure.

• Minor point:E= mc^2 is not the kinetic energy of an object with mass m moving at the speed of light. For objects with mass moving at near the speed of light, you need to use the relativistic kinetic energy equation, which approaches infinity at near-lightspeed velocities for objects with mass. Dec 31, 2018 at 19:47
• @notovny, that's a good point and a good catch. I'll update the answer. Thanks!
– JBH
Dec 31, 2018 at 20:06

Well, maybe. Sort of.

The idea would be that when acting as a superhero your protagonist's actions are powered not by his mundane physiology, but by tapping into the (chi, etc) spiritual energy produced by his body. Probably the closest approach to this is the Star Wars midichlorian bodies, which while biological also allow tapping into the field that is The Force.

Of course, relating this to body mass has its problems. First, the unit of energy production would presumably be the cell, and not all cells have the same mass. Second, this would require assuming that every cell in all magic users has the same efficiency in producing Chi energy. Otherwise, you can get someone like Luke Skywalker who has a very high density of midichlorians and much stronger Force than others of the same size.

Alternatively, your "midichlorians" might work by actually converting the mass of the cell it inhabits to effects such as powering a fist, with a conversion rate of energy to mass consumed being some factor of the e = mc^2 equation. Since individual cells in the body are not immortal, a certain amount of early cell death due to using superpowers would be acceptable, similar to the cellular damage incurred during heavy exercise. Note that, since you are invoking "spiritual" force, the rules do not need to be exactly the same as for mere material processes.