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The Science of Why Captain America’s Shield Bounces

It’s one of the nerdiest lingering questions in Marvel canon: if one of the defining features of Captain America‘s shield is that it uses the exotic metal vibranium to absorb kinetic energy, why does it bounce? Kinetic energy is the energy of mass in motion, and so if that’s absorbed on impact, shouldn’t the shield simply drop when it strikes a wall or faceless bad guy? Not necessarily.

In my latest Because Science, I’m using materials science to finally answer this question. And I think the starting point is asking a very important follow-up: if Cap’s shield does absorb kinetic energy, where does it go after that? All the oomph behind Cap’s tosses can’t just disappear. The energy has to be transformed into heat or sound or the deformation of material. However, we don’t see the shield heat up significantly, or deform permanently, or clang loudly against evil skulls. That’s only leaves one conclusion: the kinetic energy is returned to the shield.

If the materials science was completed perfectly — the shield was made by Tony Stark’s dad after all (in the MCU) — Cap’s shield could have the optimal combination of properties to make itself very bouncy. To find out what that balance has to be, check out my latest episode above!

After you watch the new episode above, check out my last video on how to build a real “deflector shield,” subscribe to this playlist to stay current with the show, buy a Because Science shirt, mug, hat, or collectible pin (the SURPRISE LIGHTSABER! shirts are in!), and follow me on Twitter to give me a suggestion for the next episode or on Instagram where I’m now posting extra mini-episodes!

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