When you hit a person, you apply a force on him. Then according to Newton's third law, there should be an equal and opposite reaction, and that should act on you. So, why don't you fall backward? Is it because opposite force from the other person is used almost entirely to stop your hand? And almost no force is used in moving/pushing you backwards.

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    $\begingroup$ Try it on skates. $\endgroup$ Sep 27, 2015 at 16:24
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    $\begingroup$ Who told you that? Seriously. Get two people of approximately the same mass on skate and have them try various pushing off exercises from gentle to violent. Or at least until they get tired of falling down. $\endgroup$ Sep 27, 2015 at 16:28
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    $\begingroup$ You don't move because you're a big person hitting little people. $\endgroup$
    – user16035
    Sep 27, 2015 at 16:33
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    $\begingroup$ Don't think. Try. You have, I'm sure, seen a certain amount of people hitting each other either in person or filmed, but those cases generally involve people in contact with the ground. That contact implies other large forces acting on the participants. Worse people react to being hit, so their muscles get into the game. SO you need to isolate those effects before you can test Newton's laws. $\endgroup$ Sep 27, 2015 at 16:41
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    $\begingroup$ Why has this question been downvoted? $\endgroup$
    – pela
    Sep 28, 2015 at 12:38

1 Answer 1


Compare this with a situation where two rigid body collide. First moving with some velocity and second at rest. After applying conservation of momentum and energy, you see that the one moving with some speed looses kinetic energy and other gains.

  • $\begingroup$ It's not because the other person will move a way. $\endgroup$
    – Alec Teal
    Sep 28, 2015 at 17:50
  • $\begingroup$ @ALec Teal What is not because other person will move away? Be explicit. $\endgroup$ Sep 28, 2015 at 18:09
  • $\begingroup$ yes , please clarify $\endgroup$ Sep 28, 2015 at 18:11

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