# How to cancel momentum without causing damage?

This is a fictional scenario I've designed and I'm trying to obtain a plausible logic for it to be somehow possible:

I have a moving object, like a car or a person running, how can I stop it instantly without damaging it? I know that in order to stop it, I could apply an opposite force to cancel the momentum, but that would surely damage it? Is there any other way to cancel it?

• Damage like crumpling only happens when the stopping force is applied unevenly. If every particle that makes up your object receives a force proportional to the particles mass then you could achieve constant deceleration without distorting the object. Then the only question is whether the kinetic energy of the object can safely be absorbed as heat by the object without melting / burning / whatever. – Brandon Enright Jun 28 '14 at 16:57
• Hmm, that sounds plausible. Now I just I've to come up with a way to disperse the heat. Can you turn that comment as answer to accept it? – jaimetotal Jun 28 '14 at 17:13
• Sure, if you do it very slowly. – John Alexiou Oct 31 '17 at 15:37

theoretically that might be possible but practically it is IMPOSSIBLE you just cant apply same force on every atom of every single molecule of the car.

and you should also see at the general formula of momentum in which force is inversely proportional to the time taken and directly proportional to the change in momentum according to your fictional scenario it will result in a very large amount of force in a very small time which will nearly tend to zero and according to the basic mathematical principles any ratio between any non-zero number with zero will result in infinity and it is mere impossible for any man or machine in this world to apply infinitive force

and if you take an example of very minute elementary particles like electrons whose weight is very small but moves with a very high velocity the result will be the same

so in short answer to your question is practically impossible but theoretically possible

• That is where fiction can enter to "make it possible" – jaimetotal Jun 28 '14 at 17:08
• yeah it can be possible with slow moving elementary particles like thermal neutrons which are release during the process of nuclear fission which are the only neutrons who are responsible for continuity of progress of fission – agha rehan abbas Jun 28 '14 at 17:13
• To stop a moving/rotating part you need to apply uneven forces throughout the object which in theory could cause damage at some point. – John Alexiou Oct 31 '17 at 15:10

You would need to apply appropriate force to all elements of the object (including those inside it) at the same time, similar to gravity force. That seems very difficult.

• By appropriate, do you mean the opposite? Wouldn't that also damage the (inner) elements? – jaimetotal Jun 28 '14 at 16:56
• according to me it will damage them for sure this condition is applicable only for elementary and sub atomic particles but surely it is impossible even theoretically for heavy bodies – agha rehan abbas Jun 28 '14 at 17:35
• @jaimetotal, I meant a force that is proportional to the mass of the element. Such set of forces accelerates each element with the same acceleration so their mutual distances may remain the same and no damage occurs. – Ján Lalinský Jun 28 '14 at 17:50