Thursday, May 29, 2008

Newton's Third: it's the law


Kevin Koch posts from his blog:

Being a former physics major has certain drawbacks. Oh, it’s a tremendous advantage in understanding how and why things move the way the do when I’m animating. But it makes it hard to enjoy some animation, when the most basic principles of physics are grotesquely violated. For example, why does the above look so wrong?

We intuitively know it’s wrong, and telling ourselves that Hancock is a super-powered dude doesn’t help much. Because even super heroes have to answer to Isaac Newton. Newton blew a lot of people’s minds by summing up much of the hows and whys of motion in three simple laws. And here’s his third law:

For every action there is an equal and opposite reaction.

Simple, huh? If I’m standing on the edge of a boat, and step towards the dock, the boat will go away from me as much as I go towards the dock. And if I’m not aware of this law, I end up all wet. If you’re sitting in a swivel chair, take that coffee mug off your desk, lift your feet off the ground, and throw the mug as hard as you can. Notice how you spin in the opposite direction from the throw? That’s Newton’s Third Law in action. Oh, and I hope you didn’t aim the mug at your officemate.

In the above clip, the law says that the force being generated at Hancock’s hands, which serves to propel an 80,000-pound whale around 600 feet in a split second, would have an equal and opposite effect at his feet. That’s assuming Hancock’s body, being super and all, is rigid and strong enough not to tear itself apart.* I’m not sure how deeply Hancock would end up burying himself in the sand, but it would be pretty deep. The whale actually wouldn’t end up going much of anywhere. Hancock would just corkscrew himself deep into the sand.

Here’s an experiment: go to an ice rink. Wear some slippery-bottomed dress shoes, pick up a very heavy object, go out on the ice, and see how far you can hurl said object. Just don’t blame me when you end up breaking your tail bone or your nose.

Of course, we’re assuming the whale above is pretty much petrified. Because if it isn’t, Hancock would simply pull two fist-fulls of flesh from the poor creature’s tail before that 40-ton mammal would budge more than a few feet. Try grabbing a big fat regular fish by the tail with a pair of pliers, and jerking it as far and as fast as you can. Yep, the fish won’t move much, but you will tear a little piece of tail away.

I know I’m being Johnny Buzzkill here, and that the filmmakers knew this was ridiculous, and that the animator was just doing what they were told, and it’s played for laughs, and all that jazz. My point is that, if you want the audience to enjoy the marvel of seeing a regular-looking dude doing something physically extraordinary, then the biomechanics and physics can’t be as trivial looking as an actor tossing a 30-pound prop, like this:


Otherwise, why bother to have the pavement exploding when Hancock lands after a huge jump? It’s kind of like watching bad Japanese monster movies, where some 120-pound guy in a suit jumps around and pretends to weigh 100 tons, but they still move like a gymnast in a rubber costume. It just looks dopey, even when the miniatures of the city being stomped to pieces look pretty good. Call me a curmudgeon, but a cursory nod to physics, even extremely exaggerated physics, make these kinds of scenes a lot more fun for me.

*Which is what would have happened to good ol’ Lee Majors, the Six Million Dollar Man, when he tried some crap like tossing a boulder with his bionic arm. The force generated at his hand would have an equal and opposite effect at the junction of his bionic arm and his human shoulder, resulting is said arm ripping loose, and much messiness from all the torn vessels and sinews and such. Not pretty, even if the sound cues were classic.


Anonymous said...

Maybe Hancock uses tactile telekinesis, like the modern Superman in DC comics. In this case, telekinesis moves the whale when Hancock touches it, not physical action.

I agree that the lack of physics hurts the shot, though.

Kevin Koch said...

I think tactile telekinesis, which sounds pretty magical to me, would keep the whale from being ripped to pieces, but it wouldn't get you around Newton's third law. There's still tremendous force be directed in one direction, and no equal and opposite force in the other.

And I know it's kind of silly arguing stuff like this (shades of old comic fanboy days!), but I think it does make a difference in how well these kinds of scenes work within a film.

Anonymous said...

I think the opposite force, in this case, would be Hancock's power of flight. It could keep him stationary while he swung the whale around.

I still agree with you that the lack of physics hurts the shot. It doesn't have to be "real" -- it has to be believable. Even if Hancock's powers work properly in the shot, the lack of physics does hurt the shot.

I also agree that I'm letting my geek side show in this conversation. :^D

Anonymous said...

totally agree with you Kev. I was so glad to see someone mention it too, I cringe every time it's on T.V!

Anonymous said...

It's strange too because from watching the rest of the trailer it's clear they were thinking of reactions - ie: when he lands from flying he chews up the asphalt). Even if they didn't shoot it right (and obviously they didn't) they could've just corrected it in CG since so much of the scene was CG. I'd be curious about who did the actual animation since even ignoring the piont Kevin made the animation on the whale is on the amateurish side.

Anonymous said...

As an animator, it is really frustating to deal with both sides of the issue. On one side, the lead/supervisor is asking you to do something you know you don't have enough frames for, on the other, said physics ARE being considered and you now have some problem solving to do.
There's also the shitty plates you have to work with, and you have to keep the sup satisfied in order to keep the hope that the studio will call you for the next project.

But I do agree the result, in this case, looks very amateurish.


Kevin Koch said...

R., I completely agree, and I tried to make that clear in the post. We've all been in exactly that place, trying to balance what we know should be done with what we're mandated to do. And after we're done with compromises we hated to make, some smart alec comes along and pokes fun at the work.

So to the animators who worked on this shot, my apologies.

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