Newton’s Third: It’s the Law

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 this look so wrong?

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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:

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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.

20 Responses to “Newton’s Third: It’s the Law”

  1. Fernando Says:

    Awesome post Kevin. It always get in my nerves when superman stops an airplane just with the hands, like the plane is made of diamond.

    On the wale, I think they would get a much better result if just a little of the weight was respected. What looks more strange to me is at a certain point the wale’s upper joints don’t affect the other joints, looks like they freeze.

    cheers

  2. alonso Says:

    Yeah, that’s always bugged me a little about super hero stuff, but what are you gonna do, if you want to obey the laws of physics you can’t have super hero’s saving falling airplanes or anything.

    the only time I’ve seen it done ok is when robocop stops a bus without moving, and then when he steps away we see the holes under his feet where presumably he anchored himself so the bus wouldn’t push him.

    I guess physics

  3. Matthew Says:

    Momentum hasn’t been conserved.

    It’s always disturbing to me to see this law broken. Why don’t studios call out instances where it’s not conserved…everyone should be able to recognize when it’s not working, since it’s happening around us all the time?! Believability is a precious thing in animation, and losing it for something as simple as this is a shame!

    Matthew

  4. Anonymous Says:

    Thanks Kevin! It’s so apparent that these kind of things really kill that illusion.. There’s a great post on Carlos’s blog that shows a clip from Iron Man that really has some great use of this theory.

  5. Blake Says:

    Thanks for such a great post Kevin! I really think studio’s should pay more attention to this sort of thing. Well I guess Directors are the many reason so of these shots come out like they do. I’ve heard of several instances where this as occured on Transformers because it was Bay’s vision, even though it was wrong. There is a great post on Carlos Baena’s blog about the correct use of weight and mechanics used in a Iron Man shot. Great stuff!

  6. Matthew Says:

    Is ridiculous, as you described it, of watching Hancock matter-of-factly toss that whale onto a sailboat, funnier than any of the options you mentioned?

    Humor in this type of film always tends towards slapstick, or just plain stupid. With all the effort spent getting the visuals looking realistic, why not keep the gags in that vein?

    I suspect many people would be more amused to see Hancock get buried in the sand and struggle to get himself out; or have a chunk of the whale’s tale torn off in his hands, followed by a pummeling from the giant mammal! Options ;)

    Matthew

  7. Jen Says:

    For what it’s worth, the modern Superman uses tactile telekinesis, which lets him lift a cruise ship without the structure collapsing. Maybe Hancock uses the same thing.

  8. Kevin Says:

    Great comments, everyone. Alonso, you’re right about the impossibility of much super-hero stuff (those guys would generate staggering levels of internal heat when they were doing super stuff, as one example, so anyone close to them would cook). But there are ways to give a reasonable nod to physics and thermodynamics and so on without being flat-out silly.

    Matthew, I LOVE your ideas. Wouldn’t that be hilarious? Here you have a guy with these powers, and he’s unable to properly use them because he has no sense of physics. What a hoot.

    Jen, the tactile telekinesis sounds a lot like magic to me. Sorry, I guess I grew up loving comics and superheros, and enjoying the intricate rules each one had. These were of course constantly violated to some extent, but they were usually exaggerations of real abilities, and I could relate to them. What I’ve read of tactile telekinesis seems to be that “it does what I want it to do,” kind of like unlimited magical powers. It’s not so interesting to me. And even still, does something like tactile telekinesis give a free pass on physics? You’ve still got that third law of Newton’s to deal with, even if the TT lets you not rip the whale to pieces. In the world of energy and forces, there is no free lunch.

  9. Kevin Says:

    Oh, yeah, and Carlos Baena’s post on Iron Man (which I apparently can’t individually link to) is great. I too thought that was a strength of the movie, and enjoyed the good job that was done on making the ‘super’ behavior relatively believable. I think in the climactic battle some things started to get excessively fudged, but up to that point I wasn’t constantly losing my suspension of disbelief because the animation/effects crew handled the mechanics and physics with style and substance.

  10. Jen Says:

    Hi, Ken,

    Hancock’s power of flight could keep him rooted while swinging the whale around, if tactile telekinesis let him pick up the whale while keeping it intact. This would satisfy the third law.

    A hero with less wriggle room in the physics department would be the Hulk, who cannot fly. The tank-spin from the 2003 Hulk film got a similar criticism from the Insultingly Stupid Movie Physics site.

    :^)

    Jen

  11. Kevin Says:

    Hmmm, the power of flight. Still a force, no? It’s some force that can drive him into the sky? A force that would blast pounds of sand all over the place (at the very least) as it was compensating for the force generated by the whale toss? I still say there’s no free lunch.

    By the way, I love the Insultingly Stupid Movie Physics site. Lots of fun. Oh, and I noticed there’s actually an even more egregious bit of physics nonsense in one of the Hancock trailers. A chubby kid keeps insulting him, so he throws the kid high into the sky. Forget for a moment that a lot of the complaints about the whale toss apply here. The part that makes me groan is that the kid comes falling back to earth about 10 seconds later . . . and he’s totally fine because Hancock catches him three feet before he hits the ground.

    Somehow instant deceleration in someone’s hands is okay, but instant deceleration on the ground will leave you a pulpy puddle of flesh. Let’s see — terminal velocity for a typical skydiver is about 120 mph. The kid’s lighter, so let’s say he was only going 100 mph when Hancock caught him. Yeah, I think that ends up pretty messy, even if Hancock has really soft hands. ;)

  12. Alej Garcia Says:

    My argument has always been that getting the physics correct in animation is like getting perspective and anatomy right in drawing. You should know the rules so that if you break them, it’s by design and not because you don’t know what’s right or wrong. It’s no surprise that movies with the worst physics in their CGI tend to be rejected by audiences because the effects look fake.

    With this philosophy in mind, the Physics department and the Animation program at San Jose State have teamed up to create physics tutorials specifically for animators. The project is just getting started but you’ll find these tutorials at:

    http://www.animationphysics.com

  13. Kevin Says:

    Alej, thanks for the link. A couple of my Animation Mentor students have mentioned you program and website (in conjunction with one of my mini-lectures on physics). I think it’s a great and useful idea, and I’m glad you’re doing it. I think I’ll do a post on it, rather than say more in the comments.

    And I completely agree with your first paragraph. That’s exactly the issue.

  14. Alej Garcia Says:

    Thanks Kevin. As I said, we’re just getting off the ground so any suggestions are most welcome. And thanks for spreading the word.

    On the original topic of this post (the whale throwing scene): Is it just me or does the whale seem to accelerate just after Hancock throws it? Looks to me like it’s jet propelled as it flies upward. Perhaps the film’s director plays golf and is used to seeing the trajectory of a golf ball accelerate when hit well with a driver. But that’s due to the spin of the ball (Magnus effect for us propeller heads). That whale is not spinning to it should fly like dead weight (literally).

  15. Kevin Says:

    Hi Alej. Yeah, I noticed that, too. I think if we saw the scene from the side, it would be really pronounced the way the whale accelerates after it’s released. Magnus effect, huh? I love learning new stuff, so thanks for that.

  16. Anonymous Says:

    Even if Hancock used some kind of telekinesis (which requires him to touch an object in order to, uh, telekinesize it) to propel the whale out into the sea, without ripping its fluke off, the poor creature would’ve been killed by the impact against the ocean, even if it hadn’t hit the boat. Some people think it would survive because the whale is built to withstand the pressure of the ocean depths, but that’s not the same as the sudden catastrophic deceleration of hitting a flat water surface. If it hadn’t somehow burst open, all of its guts would’ve been shredded inside its own body by the impact. With just superhuman strength and nothing else, the only way a superhero could save that whale would be to dig out around it until the water comes in to unbeach it. And if he didn’t have superspeed too, good luck finishing the job before the whale suffocates.

  17. Sant Arellano Says:

    KEVINN!!!

    Yes!! yes!!! Thanks to you a new world has opened up before me.

    For the whale scene, I think that if they respect the law of physics, that scene would have looked a lot cooler. Imagine watching Hancock burying himself in the sand, the thing is, the audience has never seen stuff like that so it’s hard to put your finger on what you feel doesn’t look right.

    Just now my brother was watching The Incredibles and there’s the scene where Bob is fighting the robot for the first time and to save himself from the rotating claws he throws himself into a rock thats floating on magma, since the rock is not big enough to cover his whole body, parts of Bob’s body come very close to the magma.

    And… it doesn’t look right, at that close distance, he should at least felt a very ugly burn in his face. It would have also looked awesome if smoke raised from his head.

    Thanks for posting this Kevin!!!

    Sant

  18. Sonny Says:

    nice post!
    I like Jen’s explanation on tactile telekinesis allowing Hancock to lift the whale without tearing chunks, and how the power of flight keeps him from burying himself in the sand.
    To anwer Kevin’s force question as to why his flight force doesnt blast sand all over the place – I return to tactile telekinesis – its just such a convenient thing to have around :)

    Anyway – the point of the shot is that Hancock messed up – if he didn’t mess up defying the laws of physics, then he messed up in killing the whale – with out without hitting the boat. He just hurt some extra people – the ones on the boat!

  19. Kevin Says:

    “I return to tactile telekinesis – its just such a convenient thing to have around”

    Of course, if tactile telekinesis does all that stuff, then it would also allow Hancock to come crashing into the street without damaging the asphalt, right? If Handcock has the absolute control over his flight and telekinesis powers to NOT bury himself in the sand or tear the whale to pieces, then he has the control to not throw the whale into the boat (or elsewhere to not fly into street signs or blast off a park bench and inadvertently make it disintegrate).

    In the end, you can’t have it both ways. Either he’s a dope with incredible powers (in which case, animate him that way), or he’s got staggering control over every last grain of sand while on the beach unleashing staggering forces.

    But hey, it’s just a movie, and it looked pretty funny till I saw the second trailer where they give the entire story away. Now why the hell do they do that?

  20. Joe Corrao Says:

    Ya…even though he is superstrrog and he can pick up the whale, it still looks weighless…his superstrength on the tail would probably tear it from the whale, the tail isn’t designed to carry the weight of the whole body. There should be some secondary action on the rest of the whale when he pulls from the tail

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The animation and animation-related musings of Kevin Koch