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So, watching Captain America: Winter Soldier, I think I spotted a flaw regarding to Captain America's shield properties. There is a scene where Cap is fighting Winter Soldier and his henchmen alongside Falcon and Black Widow. One of the henchmen starts to fire with a minigun and Steve Rogers uses his shield to deflect the bullets and hit another henchmen.

But, watching this scene from Captain America: First Avenger, Howard Stark explains that the vibranium, the material from which the shield is made, is completely vibration absorbent. Then, Peggy Carter shoots at the shield and the bullets completely stop on impacting the shield.

There is some explanation on how the bullets were deflected in Winter Soldier movie?

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    It seems to be vibration absorbent if fired at directly. If the shield is angled then the bounces can be directed. Frankly, though this is plot dependent.
    – Paulie_D
    Commented May 14, 2018 at 16:26
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    As I said, plot dependent. Since the shield is composed of imaginary material it can do anything the writers want it to.
    – Paulie_D
    Commented May 14, 2018 at 19:36
  • @Paulie_D guess I overlooked that mentioning..
    – Charles
    Commented May 14, 2018 at 23:53
  • Indeed, even Black Panther's nanotech vibranium suit isn't as magic as Capt's simple solid lump of it.
    – OrangeDog
    Commented May 15, 2018 at 16:13
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    I think Spider-Man answered this in Civil War: "That thing does not obey the laws of physics at all."
    – GendoIkari
    Commented May 15, 2018 at 16:35

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Even though it's just vibranium -- with Capt. having no innate relationship with this material -- the shield most often behaves in a way that perfectly reflects Capt.'s intentions at that time.

For example: He wants a bullet to stop upon contact with the shield, it stops. He wants to throw the shield and have it bounce off 12 things before coming back to him, it does. He wants to ricochet bullets off the shield to target enemies, no problem.

Any conclusions/analysis beyond this and it all falls apart.

The de facto proof of how Capt.'s shield doesn't consistently adhere to even MCU physics/claims, is the fact that Capt.'s shield nearly always produces sound upon being struck. If the shield were truly 100% vibration absorbent, then, it wouldn't produce any sound.

For Capt.'s shield to match the MCU claims, then, physically speaking, it would have to:

  1. have enough stored potential energy to sufficiently convert the external kinetic energy being applied to the shield to "manageable" internal kinetic energy (Capt.'s shield would actually be a kind of spring system); and

  2. the dampening effect of the shield (spring system) would be infinite in magnitude and instantaneously effective.

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There is really no explanation other than this is a plot hole. At times, the shield absorbs kinetic energy, as with the bullets. At others, Cap is bouncing it off all kinds of things with inhuman accuracy. There is no explanation given in any of the movies as to why this is the case.

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  • accuracy<- years of practice +expertise + super human + all and all, He's Cap
    – Vishwa
    Commented May 15, 2018 at 6:38
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    @Vishwa, I meant there's no explanation for the fact that it will bounce in the way it does when Cap throws it, not that there's no explanation for his accuracy.
    – Kevin
    Commented May 15, 2018 at 12:36
  • that's what I meant actually. the way he throws could be the reason for the bouncebacks. with years of practice and stuff
    – Vishwa
    Commented May 15, 2018 at 12:55
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    @Vishwa, but if the shield absorbs kinetic energy, like it does with the bullets, it shouldn't bounce at all, let alone going ricocheting off things like it's a Super Bouncy Ball.
    – Kevin
    Commented May 15, 2018 at 12:58
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    In some of the comics, Vibranium is described as having an absorbsion that is dependant on the crystalline structure - hit it head-on, and it absorbs all the vibration, but hit it side-on and you get a 'perfect reflection' instead. This allows the shield to stop bullets from the front, but bounce on the rim - and also gives it a way to bleed-off stored energy. Potentially hitting the front also makes the sound come out the side too?
    – Chronocidal
    Commented May 17, 2018 at 7:07
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Now I'm no expert in MCU science, but if Hank Pym can carry a tank like a key-ring, you know you have to take science in the MCU with a huge grain of salt. Nevertheless, I think that it probably has something to do with the fact that minigun bullets are faster than pistol bullets. Or at least they have a "oomph" on impact greater than that of a pistol bullet. Either way, this shows that the in the minigun's case, the shield can absorb more vibrational energy. Maybe this energy is released at the instant one bullet is blocked and the next one hits. This causes it to reflect the bullets from the minigun as shown due to its higher rate of fire, so the "oomph" from one bullet deflects the next, and the "oomph" from it, the next. Then again, GRAIN OF SAlT. Hope this helps

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I believe there's a fairly straightforward explanation for the seeming contradiction in the shield's behavior, though it's not one I've ever seen explicitly stated in the comics.

I believe the key is the shield's shape. Remember that the shield is not pure vibranium. It is a vibranium/steel alloy. This means that vibration is not absorbed completely. Instead, it is partially absorbed by the vibranium, and partially redirected throughout the disc.

If you strike the shield dead-center on the star, almost none of that energy will be directed back behind it. Instead, it will radiate out through the metal of the disc and disperse around the rim as sound. That's how Cap can block a direct blow from Thor or the Hulk, or use the shield as a landing pad after jumping from a significant height.

On the other hand, if the shield is struck on the rim, the force is almost 100% redirected around the rim, which is what allows it to ricochet with no apparent loss of momentum when Cap throws it.

Now, if the shield is struck anywhere between a dead-center blow and a rim-shot, most the energy of the blow will be absorbed, but a portion will make it through. Thus, Cap is actually more likely to be knocked off-balance by a glancing blow than by a direct hit.

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