Iron Man's suits displays a wide array of advanced technologies:

  • super-durability
  • amazing artificial intelligence,
  • virtually unlimited energy via the ARC reactors, and
  • repulsor technology

The repulsors enable flight as well is providing an offensive weapon which can be used to fire damaging blast and as well as to throw/push objects and enemies with significant force.

Now, I'm quite sure we've seen significant cases where he exerts the push without being braced against a solid object or using other repulsors for their counter-reaction.

Now, of course, Newton's Third Law of Motion states:

When one body exerts a force on a second body, the second body simultaneously exerts a force equal in magnitude and opposite in direction on the first body.

or colloquially, this is often rendered as

For every action there's an equal and opposite reaction.

Now, clearly comic book heroes violate real-world physics all the time in any number of ways. The question is about whether this violation is an actual characteristic of the repulsor technology (in-universe). So:

  1. Is there an undeniable instance where Iron Man's repulsors violate Newton III?
  2. Is this just a normal bad comic book/movie physics situation or does the technology actually overcome this law of physics in-universe (or have some other in-universe explanation)?

Here are a few blasts (at the 33s mark) where the reaction force is clearly not at all proportional to the blast:

  • cold fusion reactor ... its theoretical as of now... his suit may also very well violate laws of thermodynamic as well .. – bermuda dogs Jun 18 '19 at 17:42
  • @bermudadogs: Yes, but so what. I guess one could ask the parallel question about thermodynamical laws, but I didn't. – ThePopMachine Jun 18 '19 at 17:47
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    There are clearly moments (in the movies at least; I'm not familiar with the comics) where his flight repulsors cause collateral damage with their "exhaust" - such as his poor car collection - so it seems likely that in-universe, they're supposed to recoil all the time. If they don't in a particular scene, it's probably just artistic license. – Cadence Jun 18 '19 at 17:51
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    His repulsor technology is not the avenue I would have addressed in relation to Iron Man and any of Newton's laws. You can at least posit that his blasts when used as a weapon contain more energy than force. How about when he is shot out of the air by a tank and crashes into the ground? Or when Rhodey is accidentally shot out of the air by Vision and survives? Wrapping yourself in metal and crashing into the ground is going to kill you just as well as crashing into the ground without a metal suit. – Ellesedil Jun 18 '19 at 18:24
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    @NKCampbell: Come now, that's really pushing it. But if that is the case, that's an answer to the question too. (It would fall under "some other in-universe explanation"). Frankly, using the repulsors for flight seems pretty good explanation that Newton-III exists in-universe. Now we're getting really pedantic, I think. – ThePopMachine Jun 18 '19 at 20:22

Although the repulsor technology is absurd in many ways based on the laws of physics, for your specific objection here - which I am paraphrasing as "Sometimes Iron Man uses the repulsors and doesn't shoot backwards in the opposite direction as the force he's expelling" - I think this one objection may be at least partially addressed in the films.

During the scenes in his basement shop while devising the first "real" suit (as opposed to the one he builds in the cave), he engages in flight testing using the repulsors - flight testing which goes awry. After a certain amount of further development, he is able to control the suit. This seems to be the filmmaker's hand-wave to say, "The repulsors were initially hard for Tony to handle as the pilot, but using the suit's control surfaces and by getting flight practice, he can now account for the repulsor forces adequately."

Again, please note that I think this is absurd, but there's at least an attempt to deal with this problem in-universe.

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