# Hollywood Physics Project

• Travis Enigma
In summary, In my physics class, we are doing the Hollywood Physics Project. It's a project where you analyze the physics from a scene in a movie and talk about if it's accurate or not. I chose the scene from the Avengers where Thor strikes Captain America's shield with his hammer. The special thing about Captain America's shield is that it is made of vibranium, thus it absorbs all kinetic energy. I have a question regarding this, however, when the hammer strikes the shield I said it was a collision, therefore cancelling out mtT we are left with vT=VTF. However, something that confuses me is that Thor is sent flying backwards after the collision, so shouldn't he have a negative velocityf

#### Travis Enigma

Homework Statement
Analyze the Physics in a movie
Relevant Equations
pi=pf
Hi everyone,

In my physics class, we are doing the Hollywood Physics Project. It's a project where you analyze the physics from a scene in a movie and talk about if it's accurate or not.

I chose the scene from the Avengers where Thor strikes Captain America's shield with his hammer. The special thing about Captain America's shield is that it is made of vibranium, thus it absorbs all kinetic energy.

I have a question regarding this, however,

when the hammer strikes the shield I said it was a collision, therefore

mTvT+mCVC= mTvTf +mCvCf

Since Captain America is at rest in the beginning, and since his shield absorbs the impact he is also at rest in the end. Therefore,

mTvT= mTvTf

canceling mtT we are left with vT=VTF. However, something that confuses me is that Thor is sent flying backwards after the collision, so shouldn't he have a negative velocity? So how can vT=VTF

Also if you are interested in viewing the video for yourself, so you have a better idea here's the link it's short only 50ish seconds.

PeroK
The issue is that the combined momentum of Cap and Thor isn't in fact conserved. In other words ##p_i \neq p_f##... this is because there's an external force (of friction) acting on Cap's feet, and ##p_i = p_f## only holds if the system you're looking at is isolated!

Also, does the shield absorb all of the kinetic energy? If that were the case, Thor should just come to a complete stop, right? Since he doesn't, you must conclude that maybe those Vibranium manufacturers weren't being completely honest about the elastic properties of their material

(If the ratio of Thor's final to initial kinetic energy is ##e## [you could consider this a "material property"] then can you work out the ratio of his final to initial speed?)

PeroK
Oh, I see, I completely disregarded the fact that friction still acts on Cap. But what about the conservation of energy? I feel like air resistance would be negligible at this point if considered the strength of Thor's hammer. The kinetic energy of the hammer is transferred into light and sound energy when it collides. Would that be right? Did marvel get their physics right at least for that?

Oh, I see, I completely disregarded the fact that friction still acts on Cap. But what about the conservation of energy? I feel like air resistance would be negligible at this point if considered the strength of Thor's hammer. The kinetic energy of the hammer is transferred into light and sound energy when it collides. Would that be right? Did marvel get their physics right at least for that?

That's true, but Thor goes flying back too! It's a bit like throwing a ball at a wall; some of the initial kinetic energy is lost as heat, sound, whatever, but if the ball rebounds with non-zero speed then it still carries some kinetic energy that you also need to account for.

You could try and estimate his initial speed and his rebound speed, find the difference between the initial and final kinetic energies and hence deduce what proportion of the initial energy was dissipated.

Thanks so much, I'll start working on that.

It's annoying that the bit you want to analyse is in slow motion... makes it difficult to estimate speeds

There's some ways to get around that. If you can estimate the maximum height of Thor's parabolic trajectory, as well as his final height upon impacting Cap, you can calculate how long he spends in the air, as well as the vertical component of his velocity upon impact. If you can also write down an estimate for his initial horizontal displacement from Cap you can further deduce his horizontal velocity upon impact by simple division. Same goes for his trajectory after the impact.

Maybe that's a better approach than trying to figure out by what factor the video is slowed!