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Introduction

Many videogames and other fictional worlds portray mages or wizards casting personal shields around themselves or in defense of other party members. These are often alike from fictional work to fictional work, appearing as glowing domes or bubbles that wrap around the mage or the target of the spell. Less commonly, magic shields look like glowing shields that are either worn like a normal shield, or thrown up as a barrier against an incoming attack.

These shields act as defensive barriers, absorbing blows that would otherwise hit the target. They typically deplete after a while, and will fade faster under harder and more frequent blows.

With the advent of more modern weaponry (firearms in particular), how will the shape of a shield effect its ability to deflect high-velocity kinetic projectiles?

Q1) Do domes, shield shapes and bubbles make the cut vs firearms based on their structure?

Q2) Can anyone tell me if there is a physics-based reason why these shapes/structures might be so popular in the first place?

Q3) Is there any way magical shields could be improved by altering their shape/structure alone?

Please assume for the purpose of these questions that, for any shield shape:

  1. Shields are powered by a depletable resource (such as mana).
  2. Shields are entirely defensive in nature.
  3. Shields provide a thin, but entirely solid, barrier against physical objects.
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closed as primarily opinion-based by Aify, Hohmannfan, John Dallman, Green, Thucydides Oct 4 '16 at 18:20

Many good questions generate some degree of opinion based on expert experience, but answers to this question will tend to be almost entirely based on opinions, rather than facts, references, or specific expertise. If this question can be reworded to fit the rules in the help center, please edit the question.

  • $\begingroup$ Are you looking for magic resistant, negation, absorption or reflection? or all of the above! These properties aren't affected by forms/shapes unless you have a theme e.g. religion so shape that suggests a symbolic meaning would be more powerful instead. $\endgroup$ – user6760 Oct 4 '16 at 5:47
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    $\begingroup$ I completely disagree with this being put on hold, and I suspect the people who voted to close it didn't closely read the question. With the qualification: "what deflects high energy projectiles the best," this is a scientific matter of armor shape vs. projectile, and can be answered by using known real-world principles, extrapolated to a fictional armor type. $\endgroup$ – Azuaron Oct 4 '16 at 19:54
  • $\begingroup$ I agree with @Azuaron i can't see nothing opinion-based in this question. $\endgroup$ – Westside Tony Oct 5 '16 at 15:28
  • $\begingroup$ Thanks for editing my question @Azuaron! It's a lot clearer than when I originally posted it. Do you think changing the title of the question might help it being taken off hold? (I'm new on this site and don't yet understand how to do things). $\endgroup$ – MannerHouse Oct 6 '16 at 1:48
  • $\begingroup$ The title's fine, I think. What happens is, when you make an edit of an "on hold" question, it goes into a queue to be checked by a moderator and re-opened. Once someone with appropriate rep comes along and checks the queue, they can either re-open it, or shut down the question. Just have to be patient. $\endgroup$ – Azuaron Oct 6 '16 at 13:35
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Q1) Do domes, shield shapes and bubbles make the cut vs firearms based on their structure?

To examine this, it's pretty easy to look at breastplate designs after firearms became a popular weapon. You'll notice that the breastplate is not a simple curve, but has a central ridge. The reason is to try and divert a projectile from its most probable trajectory. You're much more likely to be attacked from the front, so having armor in a wedge shape was important to deflect the projectile from the center of the body to the side. This comes at a risk (shots coming from slightly to the side will hit more straight on), but most shots most the time will have their effectiveness reduced.

Q2) Can anyone tell me if there is a physics-based reason why these shapes/structures might be so popular in the first place?

No, of course not. It just looks cool, and it makes simple sense. Since magical force barriers have never been battle tested, those criteria will determine what's going to be most popular, even if different shapes would actually be more effective.

Q3) Is there any way magical shields could be improved by altering their shape/structure alone?

Absolutely. The problem with a sphere/bubble is that any attack hitting it dead on with have to be stopped instead of deflected, and deflecting an attack takes a lot less force than stopping it. Further, a sphere/bubble with it's center on the person is most likely to be head dead on a lot, since people will be aiming for... the person in the middle.

So, if the wizard knows where the attack is coming from, s/he can work to deflect it. If you've read any of the Dresden Files books, you'll notice Harry Dresden frequently uses his shields in a flat angle to deflect attacks coming from a specific direction. If you're getting attacked from absolutely every direction, a sphere can make some sense, but that is rarely the case. This means you can make shields designed to deflect attacks just enough to miss you from the direction you expect.

You can also look at how fortifications changed following the rise of cannons. Straight and curved walls were terrible at deflecting cannon blast, so people started building star forts. This isn't a perfect transfer (much of the star fort design is to channel charging infantry into kill zones), but you can see how a modified star shape would be able to more effectively channel projectiles away from your body than a sphere, even when being attacked from every direction. The points of the stars can protect you from side shots that would threaten a simple wedge, and the shots that do hit a plane head-on aren't actually pointed at your body, so if they break through you still aren't dead.

The biggest danger with the star shape is the concave points. But, since you aren't actually worried about charging infantry, you can have deliberate gaps here that lead to another interior star barrier that still channels projectiles away from your body. That way, there's no point in the shield that needs to stop a projectile, just redirect it.

Nested star shield

Seen here, the circle is the mage, and there are two nested six pointed stars. The best design would require some more design work and careful consideration of the angles (and, therefore, number of points), entry point size, and if projectiles that entered the first barrier could be redirected to exit again, instead of needing to be absolutely halted by the internal barrier. But this is a good place to start.

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Everything depends purely on your magical shield nature/properties. By your will it can just destroy high velocity projectiles upon impact or even bounce them back at the attacker.

Following is written, assuming your magical shield has some properties of material object, otherwise the question of shape is mostly cosmetic.

A2:

Spherical shapes are used in armor welding to deflect slashing hits, making them to lose force due to slipping (less force from hit goes directly to armor = less chance to break armor). Also spherical shapes are good to contain crushing blows due to better force redistribution, when directly hit (in comparison with flat armor shapes).

I think this is one of the reasons, why magical shields are depicted spherical along with nature of different forcefields like magnetic or gravitational, which tend to be "spherical": enter image description here

However even spherical shape can't make a bullet/arbalest bolt slip off a fragile armor due to a bullet's/bolt's high impact force. Making medieval armor, that could make a bolt slip was nearly impossible as there were no materials both hard and light enough to allow a soldier to fight efficiently, while wearing one.

Here could've been some references about "perfectness" of spherical shape in geometrical sense and about spherical shape, met in nature (such as planets shape, shape of the falling waterdrop, etc.), however I'm unable to find good articles in English

A1:

Yes, but only if the material has enough hardiness to stop the bullet. However I can't tell for sure if word material is appliable when talking about magical shields.

With enough hardiness shape will actually play a role: spherical shield should be used when you want shield user to avoid being hit at less cost (less direct force applied to shield), while flat should be used, when you actually want to stop the bullet (avoid ricochets).

A3:

No, the sphere is perfect in all cases, unless your magical shield has some "magical" restrictions (like bigger energy consumption per square inch of it or less shield "density" with bigger shield area).

P.S.: Sorry for bad English. Any help with grammatically improving this answer is highly appreciated.

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    $\begingroup$ A very comprehensive answer which I agree with completely. I would only add that to improve the shield structurally, thin, concentric layers may be "cheaper" to build/ cast/ maintain than a single thick layer. $\endgroup$ – Xenocacia Oct 4 '16 at 8:01
  • $\begingroup$ >may be "cheaper" to build/ cast/ As I mentioned at the start of answer: it depends purely on the nature of- and laws appliable to- the magical shield. You can make up thousands of laws and restrictions to make one or another shield shape/type to be more preferable (probably even taking in account current weather or moon phase). $\endgroup$ – haldagan Oct 4 '16 at 8:12

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