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We know that from Newton's third law of motion that to every action there is equal and...

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kumarvaibhav123 | Student, Grade 11 | (Level 1) Salutatorian

Posted September 10, 2012 at 5:18 PM via web

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We know that from Newton's third law of motion that to every action there is equal and opposite reaction but what is the reason for this equal and opposite reaction?

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glatzos | Middle School Teacher | (Level 1) Adjunct Educator

Posted September 12, 2012 at 10:52 PM (Answer #1)

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The reason is that if it did not, you wouldn't be able to take a step forward and walk for example. If you think about it, if you place your foot on the ground and push off of it, you accel forward because the ground is pushing back on the bottom of your foot with an equal but opposite force. If it did not, your foot would sink into the ground. 

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kavya--kammana | Student, Grade 12 | (Level 1) Valedictorian

Posted September 14, 2012 at 6:56 AM (Answer #2)

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theses are some points when we study abt 3rd law of motion.:

  • when we move forward the force applied on the floor is in the opposite direction of motion.
  • the floor is exerting a force on the feet in the opposite direction.
  • hence we move forward.


  • we move  in the opposite direction of applied force.
  • we apply a backward force on the floor this is our action.
  • then the floor exerts a equal force on us in the opposite direction this is our reaction.
  • if the floor didnt exerts an equal and oppposite force we will  not move forward.
  • because that force enables us to move forward.


  • the action and reaction is not in the same direction.
  • look at an example
  • people walking on smooth wet surface slip down.

if the surface is smooth and wet , we cannot apply sufficient force for the forward motion due to less friction.

as there is no action, there will be no reaction. so they slips down.

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