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Energy shields are pretty common things in fiction, with some being nebulous things that cloak you in a protective shield that absorbs damage that could otherwise harm the user, and others being literal shields from medieval times, but energy based instead.

What I would like to address here is the practical considerations that would come into play regarding surrounding yourself with an energy based force-field.

I think that some of the Halo lore regarding Spartan shields seems like it comes the closest to making a reasonable level of sense. For those that are not familiar: the shield acts like a sort of frictionless surface, that would cause the soldier to otherwise slide around or be unable to properly interact with objects or the environment if the shields were not 'tuned' to be weaker around the hands and feet. Which then raises the interesting question to me, if I were to tightly close my fist, would that not drain resources from the shield? Or If I were to high-five someone, would that not also have the same effect? An additional consideration is that the shields of the universe are impermeable, as covenant ships needed to lower a section of shield to actually fire out of them. So in summation, we have an energy shield that acts like a solid.

I'm using a similar type of technology in one of my stories. A super soldier in powered armor, cloaked in a protective shield of energy. This soldier will encounter human enemies as well as creatures. The question here is, does it make sense for the super soldier to punch an enemy with his shields up? Would it be sort of the trope of head-butting someone, where "nobody wins", and drain the shields tremendously, or would it have a fairly negligible effect?

I recognize that this by itself is not a sufficiently concrete question, so let me define a few things so we can drill down and perhaps reach a more definitive answer.

The Soldier:

  • Through augmentations as well as the strength granted by the power suit, is able to bend steel prison style bars, and can flip the equivalent of an ambulance or fire truck (with effort).

The Shield:

  • Can take a 30 round magazine of .308 bullets before failing.
  • The shield is very energy efficient when it is maintained at full strength, and can remain operational for days or weeks before a battery recharge becomes necessary, but can only refill the strength of the shield 10-20 times from combat before needing a battery recharge.
  • The user of the shield is entirely unaffected by any attack. An example: if a medieval knight was slapped, he wouldn't feel pain due to helmet and padding, but his head would be moved by the recoil. In this case, the soldier doesn't even experience the recoil as the shield completely takes it.
  • It is physically impossible to 'defeat' an acute section of the shield and bypass it: it must totally fail for the user to be affected.

So with all this in mind, if the soldier needed to put his full strength into striking a creature, does it make sense for him to attack with the shields up, or should he lower them around his hands to preserve their strength, and make himself vulnerable as well as put wear and tear on the suit?

Addendum: The minutiae of how the shield technology works, etc, are obviously subjective, and greatly affect the cost benefit analysis of whether hand to hand combat in this case would make sense. However, the objective question here is revolving around the kinetic energy of said punch/kick or strike and how it compares to the kinetic energy of the 30 rounds of .308.

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    $\begingroup$ Seems opinion-based: The shield works the way you want it to work. Foundation shields are near-perfect, while Dune shields have complex drawbacks. $\endgroup$ – user535733 Jun 4 '18 at 18:37
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    $\begingroup$ it really depends what your shield is actually stopping, if its draining the bullets of their kenetic energy like a magnetic field you can probably be punching for a good half-hour. if on the other hand it serves as more of a physical barrier with actual mechanical properties its possible it could go down in a single punch $\endgroup$ – Ummdustry Jun 4 '18 at 18:44
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    $\begingroup$ @Alexander .308 seems to average out at a muzzle energy of 3,600 joules. A quick google says the average punch is about 80 joules. That means a full mag of .308 at point-blank range would impart around 108,000 joules of energy, or 1,350 average punches. How the shield deals with that energy is up to you. $\endgroup$ – UIDAlexD Jun 4 '18 at 19:09
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    $\begingroup$ @Raznarok, I already answered below, but then thought about this and had to ask/mention it. The shield is entirely preventing recoil, and seems to work the same in both directions, (since it has to be lowered to shoot) so a punch may not be possible with the shields up. The shield seems to be dissipating kinetic energy perfectly, and if it is identical on both sides, it will do that for the opponent as, well. (Just like when trying to pick something up) So maybe the punch would just... stop $\endgroup$ – Josh Jun 4 '18 at 19:33
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    $\begingroup$ @Raznarok Elaborating on my previous comment, the shield must be being maintained at a set distance from the suit's surface, so maybe the punch would force the shield inside the punched surface, instead of just stopping. (if the shield is a continually created force) That could have... interesting results... This and my previous comment are purely fictional speculation. Since the shield isn't made of a real "thing," you can use or disregard these as you wish. They're just ideas :) $\endgroup$ – Josh Jun 4 '18 at 19:36
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Disclaimer: I am not a physicist or a mathematician. I'm a programmer. I've done my best here, but I can't guarantee my results. The biggest point of doubt in my mind is whether Joules per punch can be fairly guesstimated from Joules per truck flip.

The muzzle energy of a .308 is 3,590 Joules. The force of a punch varies, of course, but even looking for a rough estimate, I found a wide range of answers ranging from 100-1200 Joules. Your super soldier probably has a pretty nasty punch - let's see if we can get an estimate for him. You say he can flip an ambulance (14,000lbs) or fire truck. I couldn't easily find the weight of a fire truck, so we'll proceed with the weight of an ambulance. You say that takes some effort. I'm going to guess you mean that it takes him about 5 seconds. If someone lifted something any slower than that, I'd think they were struggling with it, and I don't think that's what you had in mind. Since you're referencing Halo, I'm thinking that by "flip" you mean push it upright from on it's side. An ambulance can be up to 96" wide and 110" tall. We'll ballpark that to 100x100". When "flipping" you don't bear the full weight of the flipped object. I found this pdf that says that to flip a 550 lb tire, you will lift about 275 lbs at most. (about half) Put all this together, and at your soldier's greatest point of exertion, (midway through the flip) he's moving about half an ambulance's weight (7000lbs/3175kg) about 31"/.8m (the "flip" follows a quarter-circle path - that circle has a circumference of about 628", so 157" is a quarter of that. We're interested in the 1/5th where he's doing the most work, or about 31" of it) in about 1 second. That means he's using 2,032 Joules of energy. (J=(kg*m^2)/s^2) That's using his whole body. Even a well-trained punch will not be able to deliver that amount of energy. Most people can exert more force with their legs than their arms, and we're talking about only 1 arm, but a well-trained punch includes a forward step and a twist from the core muscles, so we'll be generous and say that your soldier can deliver 1/2 of that energy with a single punch, or about 1,000 Joules.

Your shields fail at about 30 rounds of .308s, or 107,700 Joules. That's about 107 punches.

At this point, what you need to consider is:

  • How long does it take to lower the shields around the fist?
  • How expensive is the technology required to allow the shields to be locally lowered in that manner?
  • How often is the soldier going to need to punch?

With that determined, you can do a cost/benefit analysis. In the real world, I think hand-to-hand fighting on the battlefield is probably rare enough that it's not worth building in the ability to lower the shields for those rare instances, especially when considering the time and forethought it would take to lower the shields before throwing a punch. In your world/story, maybe it's different. That's for you to decide.

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  • $\begingroup$ Seems like a reasonable conclusion. Finding the KE of any particular bullet is fairly straightforward but I wasn't remotely confident on how to find out the joules of lifting/striking. The soldier unfortunately is going to be in a situation where melee will HAVE to happen. So you're probably right that the suit wasn't designed for that purpose. $\endgroup$ – Raznarok Jun 4 '18 at 19:20
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    $\begingroup$ You may want to have the option to disable the shield at the hands for non-combat purposes, though. If the shield is not affected by interactions with other objects, that means you can't actually touch anything while the shield is on. $\endgroup$ – Chris M. Jun 4 '18 at 19:21
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    $\begingroup$ @ChrisM., I think that's handled by having the shields be weaker (or nonexistent?) on the palms and undersides of the fingers, which could be a permanent state for the shield. If the option is already built in, though, you're right - that does remove a big barrier to the functionality. $\endgroup$ – Josh Jun 4 '18 at 19:25
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With shields functioning as you described, "Punching with shield active" is definitely going to have value; precisely how much value depends on a lot of numbers and can be pretty trivially adjusted to reach the world you want.

The key part of this answer is this property you listed:

The user of the shield is entirely unaffected by any attack. An example: if a medieval knight was slapped, he wouldn't feel pain due to helmet and padding, but his head would be moved by the recoil. In this case, the soldier doesn't even experience the recoil as the shield completely takes it.

Assuming that the shield can't tell the difference between being struck by an object and striking an object, that means a punch with the shield active cannot be stopped except by the shield depleting. Stopping the punch is identical to recoil in such a scenario. Anything hit by that punch would have to move or break, with the only exception being another shield. I'll get to that later.

So how would that affect combat? As I said at first, it depends a lot on how the shield depletion compares to the things you're punching. If you want the super soldier to punch through several inches of solid steel no problem, that's within reason. You could make that possible, but it depletes the shield a lot so it's more a "last resort" or "special circumstances" tactic. Or maybe the shield would deplete before you finish, and it's normal for the shield to turn off during a punch because a broken hand is better than no shield. All that has to do purely with numbers that don't exist, and which you can make up to suit your needs.

One thing which is certain though, if someone with an active shield tried to punch someone else with an active shield, at least one of those shields would deplete instantly, otherwise at least one of them would fail the "prevent all recoil" requirement. One option is to have both shields always deplete regardless of relative charge, which would make it a high-risk move in desperate situations. On the other hand, if both shields are depleted at the same rate and whichever depletes first breaks, then this could be a very high-priority move in single combat, with just a few more bullet hits than your opponent closing for a punch can end an engagement quickly. Still risky (even the "victor"'s shield takes a lot of damage, but it helps the combatant with an advantage close things out rather than providing a comeback opportunity.

In terms of punching things with neither armor plating nor an energy shield, there's probably not much benefit to leaving it on unless you're worried about secret traps. On the other hand, there's also not much cost; anything soft enough that it could be safely punched without the shield probably wouldn't deplete the shield significantly at all. I would leave it on just to be safe.

TL;DR: Punching with the shield on is probably a good idea if punching without the shield is a good idea, and possibly in other situations as well. The main reason I can see to turn off the shield to punch is if punching is already a bad idea.

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  • $\begingroup$ Interesting points, especially about the traps. I could definitely see why you would want to keep them up if you had a sort of exploding creature to deal with. I definitely appreciate the ideas/balancing, but in the interest of keeping the question objective, a "correct" answer would need to involve a kinetic energy calculation. $\endgroup$ – Raznarok Jun 4 '18 at 19:37

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