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I can’t imagine a blockbuster movie about superheroes without some cool physics. After all, these aren’t dramas, but action movies with jumping and flying and punching. Of course, the point of the jumping and flying and punching is to advance the story, not provide a physics lesson. But nothing says they can’t do both.

The first trailer for Thor: Ragnarok provides a great chance to do this. The physics lesson comes at the end, when Thor meets The Hulk in an arena. They run toward each other at top speed, then jump into the air for what I’m sure will be an epic collision. This being a trailer, Marvel doesn’t reveal what happens next, but I think it’s safe to assume Thor delivers a pretty serious blow. I’ll model this collision in two ways—the Hollywood way and the real way, because of course the Hollywood way is not at all how a real-life Thor and the Hulk would collide. And yes, I essentially just said superheroes are real.

The Hollywood Collision

Let me set up the physics for you. The Hulk definitely weighs quite a bit more than Thor. For the sake of argument, I’ll say he has three times the mass of Thor. Seems reasonable. Watching the trailer, it looks to me like Thor and The Hulk run toward each other at similar speeds and jump about the same height, colliding in the middle of their trajectory. In this model, which is what I expect to see in the movie, Thor punches The Hulk with great force, sending the green giant flying.

Here is a simulation I made using Trinket. Click play to run it as often as you like. If you want to look at the code behind it, here you go.

No one would complain with this outcome, even if this just isn’t how physics works. Even if this is how it plays out on screen, I will still enjoy the movie.

The Physics Collision

OK, now let’s look at what would really happen. Do you know what makes this collision so great, aside from the fact it features Thor and The Hulk? Both of them are in the air. That means only two forces act on them. The first is gravitational force pulling them down. Boooring. The second is the force Thor exerts on The Hulk when he lands the punch (or hits him with a club). But wait! If Thor pushes on The Hulk, The Hulk also pushes back on Thor with a force of equal magnitude in the opposite direction.

Remember, force is nothing more than an interaction between two objects. If Thor pushes The Hulk to the right with a force of 1,000 Newtons, then The Hulk pushes back on Thor to the left with a force of 1,000 Newtons. That’s just the nature of forces.

So what does this mean for Thor and The Hulk? The momentum principle says the total force on an object changes that object’s momentum, with momentum being the product of mass and velocity. So you see what must happen here: Thor and The Hulk have essentially the same total force during the punch (assuming everything happens so quickly that I can ignore gravity), and so they will experience the same change in momentum. However, given that The Hulk has three times the mass of Thor, he will experience a far smaller change in velocity.

Now for a simulation.

No matter how hard Thor hits The Hulk, he is going to get thrown back. It’s just physics. Now for a bonus gif.

hulkthor_1-1.gif

This is similar to the numerical calculation above, but real life. The two carts have different masses, but the same magnitude force acting on them. You can see that Thor loses every time. But, as I said, I don’t expect the movie to use the best physics. And honestly, I am OK with that. It’s just a movie. However, I think you can still have a physics-like collision and be part of the story. If Marvel made me the science advisor, I might suggest the scene unfold like this:

Thor and The Hulk run toward each other for their epic showdown and leap into the air. In his rage, The Hulk doesn’t notice that Thor is about to land the first blow. Thor whacks him mightily, dazing The Hulk but flying back across the arena into the wall. Thor gets up, adjusts his helmet, and tells Atlas, “Physics still works in this universe. I forgot that the beast has a larger mass than mine and momentum is still conserved. If I had my trusted weapon, Mjolnir, its significant mass would surely win the day.”

Maybe that’s why you don’t see physics professors writing movie scripts.

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