# Movie physics

Hello, I am currently working on analyzing the physics in a movie for a project.

The scene in particular that I am reviewing includes two characters (one holding the other) that smash through a series of walls and windows without getting hurt or losing speed/momentum. Can anyone tell me specifically which laws this defies and how? Thank you!

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DaveC426913
Gold Member
Hello, I am currently working on analyzing the physics in a movie for a project.

The scene in particular that I am reviewing includes two characters (one holding the other) that smash through a series of walls and windows without getting hurt or losing speed/momentum. Can anyone tell me specifically which laws this defies and how? Thank you!

What are your views on the matter?

What are your views on the matter?

I think that it defies the law of conservation of momentum because it is impossible that the characters would not lose speed after a collision of that magnitude.

SpectraCat
I think that it defies the law of conservation of momentum because it is impossible that the characters would not lose speed after a collision of that magnitude.

That sounds like a good place to start ... and your point is reasonable. However, you might wish to consider some questions a bit more carefully. For example, how do you *know* they didn't slow down? Do you know how fast they were moving to start with? Did you measure it by analyzing the film frame-by-frame, or do you mean that it just *looks* like they don't slow down to you, i.e. you don't notice any obvious difference in their speed. Can you estimate by how much you would expect them to slow down if the walls were made out of bricks, or perhaps drywall?

These are all questions that *I* would want to at least have thought about if I were going to embark on the project you describe.

Anything else bothering you about the scene physics-wise?

That sounds like a good place to start ... and your point is reasonable. However, you might wish to consider some questions a bit more carefully. For example, how do you *know* they didn't slow down? Do you know how fast they were moving to start with? Did you measure it by analyzing the film frame-by-frame, or do you mean that it just *looks* like they don't slow down to you, i.e. you don't notice any obvious difference in their speed. Can you estimate by how much you would expect them to slow down if the walls were made out of bricks, or perhaps drywall?

These are all questions that *I* would want to at least have thought about if I were going to embark on the project you describe.

Anything else bothering you about the scene physics-wise?

Thank you very much, I was looking at their speed from observations (I did not notice the speed slowing down) but I will definitely be more specific. If you are curious, the project is on a website (www.lianaandcarmen.webs.com[/URL]) and the page I am responsible for is "Bad physics", and the video for this scene is located near the bottom of the page. I am just not sure how I would calculate the speed. I know that the characters should have fallen after the first crash for sure, if not because of the force then by projectile motion. (It is a superhero movie so they are 'flying'). I really appreciate your help, thanks again!

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SpectraCat
(It is a superhero movie so they are 'flying')

Well, I wouldn't worry much about physics then, simply because there are too many unknowns. If they are "super-strong" then they could easily punch through walls, right? If they can 'fly' by shooting mystical juju-magic out of their boots, then they could easily be accelerating through each wall collision, in order to compensate for any loss of momentum, right?

Not sure there is much you can do to 'debunk' this scene, because it is not drawn from reality to begin with. The other two examples on your site don't suffer from this issue *as much*, because they deal with passive environmental effects, rather than interactions dealing with the super-characters themselves. But in this case, there seems to be little hope of a physically sensible analysis. Furthermore, if you are willing to accept a world in which super-powers can exist, don't you have to also accept that the laws of physics in that world must be different as well? So if you were to raise any of these issues with the creator/director, couldn't they always have an "out" by just saying, "That is an aspect of the alternate reality we are trying to create"? This point is one of the biggest issues with certain types of sci-fi flicks ... once you let stuff get too far out of hand with "super-powers" or omnipotent alien races, you run the risk of losing your audience because they can't relate to the "alternate reality" you are trying to portray.

Ok, well, that got a little off topic, but I hope I made my point clearly.

DaveC426913
Gold Member
I'm not sure I would go as far as SpectraCat. We can assume the laws of physcis apply within the movie with the exception of the source of their powers.

If they are flying characters then, yup, all bets are off. You can't demonstrate that their flight is not involved in the battle.

But if they weren't flying, and one punched the other, putting the second in ballistic flight, then all physics could apply.

I suppose I should chose a scene that does not involve their powers too much then. Do you have any suggestions/ideas of laws that could be broken that do not change because of their superpowers? I have a couple ideas but somehow they all involve super powers in some way or another.
1. A character gets thrown at the floor and the floor breaks
2. Characters thrown out windows without sustaining injuries or scratches (an example from intuitor movie physics website)

The whole movie is one giant example of bad physics, the only problem being they are all super heros. Any input is greatly appreciated :)

SpectraCat
If they are flying characters then, yup, all bets are off. You can't demonstrate that their flight is not involved in the battle.

Yes, the scene in question involves flying characters, so .. ixnay on the ysicsphay there.

But if they weren't flying, and one punched the other, putting the second in ballistic flight, then all physics could apply.

Right, that is what I meant by "passive environmental effects" in my post. I think you can even make a good argument that audiences should *expect* the laws of physics to apply in such cases. As far as I can tell, that is the basis for the website created by the OP. I skimmed their analyses for two other movie scenes on the same site, and they seemed pretty good ... I'd like to go back and read them in more depth if I have time.

SpectraCat
I suppose I should chose a scene that does not involve their powers too much then. Do you have any suggestions/ideas of laws that could be broken that do not change because of their superpowers? I have a couple ideas but somehow they all involve super powers in some way or another.
1. A character gets thrown at the floor and the floor breaks
2. Characters thrown out windows without sustaining injuries or scratches (an example from intuitor movie physics website)

The whole movie is one giant example of bad physics, the only problem being they are all super heros. Any input is greatly appreciated :)

As DaveC pointed out, once a character is punched, or thrown and released, then it seems reasonable to expect their trajectory to obey Newton's laws of motion. The whole "flying through a wall without a scratch" thing seems trickier though, because their super-power could involve invulnerability, right? What you have to do is look to see if they get injured in other scenes, ala the old classic "little trickle of blood out of the left corner of the mouth". That would at least be a logical, if not a physical, inconsistency.

Other examples that are often treated badly in movies are invisibility (where does the food in their stomach go?), and Newton's third law with respect to characters with super-strength. In the latter case, most super-characters at least appear to weight the same as a normal human ... that means their inertia is comparable to a normal human. Yet you will see crazy things where they can whirl a train car around their head or some thing like that ... draw the free body diagram for that process and you will see how absurd it really is.

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DaveC426913
Gold Member
http://www.popsci.com/entertainment-gaming/gallery/2008-01/superhero-physics

any thoughts on this subject? There is a similar character in the film I am analyzing.

Ouch. He's the worst. Where to start? I mean, he is the acme of bad physics because, well, he is virtually omnipotent. Where do you start anaylzing a character that can fly faster than the speed of light and go backwards in time?

There is a hilarious essay - written by my favoritingest author evar, Larry Niven - called Man of Steel Woman of Kleenex that goes into the challenges he faces in his hypothetical attempts to procreate. It is short and well worth the read - http://www.rawbw.com/~svw/superman.html" with permission.

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Ouch. He's the worst. Where to start? I mean, he is the acme of bad physics because, well, he is virtually omnipotent. Where do you start anaylzing a character that can fly faster than the speed of light and go backwards in time?

Very true, except the character in my case only has the ability to create fire with his hands and throw flame balls in and not all of that other terrible physics. (Keeping in mind the project I am working on is only for high school)

DaveC426913
Gold Member
...the ability to create fire with his hands and throw flame balls...
Well, that doesn't sound much like Superman...

The big question for most energy projector supers is: where do they get their energy/fuel/materials from? I mean, even if we grant them some weird metabolism that can do whatever conversions are necessary, the thing that these supers can never handwave is conservation of mass and conservation of energy. Do they convert their own tissue fuel? Or directly into fireballs? i.e. do they walk away from a battle five pounds lighter? Or does the fuel just funnel in from some other dimension?

That's the biggie. All other physics problems will come second to that.

BTW, is it a Marvel character? A DC character? Or other?

Well, that doesn't sound much like Superman...

The big question for most energy projector supers is: where do they get their energy/fuel/materials from? I mean, even if we grant them some weird metabolism that can do whatever conversions are necessary, the thing that these supers can never handwave is conservation of mass and conservation of energy. Do they convert their own tissue fuel? Or directly into fireballs? i.e. do they walk away from a battle five pounds lighter? Or does the fuel just funnel in from some other dimension?

That's the biggie. All other physics problems will come second to that.

BTW, is it a Marvel character? A DC character? Or other?

It is a character in a Disney Movie called Sky High Each character has a different super power and they are all training together at a high school for super heros. I am going to use the flaming character because I think that I can work with that one the most.

SpectraCat
There is a hilarious essay - written by my favoritingest author evar, Larry Niven - called Man of Steel Woman of Kleenex that goes into the challenges he faces in his hypothetical attempts to procreate. It is short and well worth the read - http://www.rawbw.com/~svw/superman.html" with permission.

I first saw that essay many years ago, but it still makes me laugh every time I think of it. Niven was a bit of a perv, but still an excellent writer.

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How can I apply thermodynamics to calculate the amount of energy required to create flames of a certain temperature? (I have not yet studied this topic in school)

The best quick example of bad physics is anything involving Superman. Unless he's so talented that he can engage his flight powers in direct response to the backwash from his super-hits, he should be flying backwards since it's the amount of friction underneath your feet that really dictates how hard you can his someone.

If you slug someone while you're in mid-air, sure, it'll hurt; you might even make them cry. But if you really want to break their sternum/jaw and send them to the hospital, then you had better have something for your body to push against. [i.e. the ground]

Since Superman can fly, obviously this argument isn't really all that valid. However, he has plenty of enemies that are at least as strong as he [Like Doomsday] that don't suffer much from recoil. There should be a crater formed under them with every punch, but, obviously that's not the case.