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Thread: can any one answer this question?????/

  1. #1 can any one answer this question?????/ 
    Forum Freshman almirza's Avatar
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    hi friends,

    I think all of us know Newton's third law of motion and one of the applications of this kaw is our walking system
    when we push the earth the earth push us with same size of force forwards
    But what i want to ask , since the two forces are equal in size and opposite in direction and they are in the same line at the same time SO WHY THE RESELTANT FORCE THAT MAKES US WALK IS NOT ZERO??
    ??


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  3. #2  
    Universal Mind John Galt's Avatar
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    This is off the top of my head, so it may be completely wrong.

    Walking is actually a process of controlled falling down. Motion is delivered by leaning forward so that the centre of gravity moves outwith the base provided by the feet resting on the ground. The body begins to fall. We bring a leg forward to reposition our centre of gravity.
    The action reaction between feet and ground merely stops us falling all the way to the centre of the Earth.


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  4. #3  
    Forum Ph.D.
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    We're applying force with our feet at an angle to the earth, not straight down. For example, step forward with your leg. How are you propelling yourself forward? Your right heel is pushing back on the earth, and the earth is pushing your foot forward. You can feel that force in your foot, just like when you are standing still you can feel the force of the earth pushing up on your feet (your weight)
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  5. #4  
    Forum Professor
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    We push on the earth with a certain force, and the earth pushes back at us with exactly the same force. Since the earth is pushing on us, we move. Since the earth is so much larger than us, it doesn't move.
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  6. #5 Re: can any one answer this question?????/ 
    Forum Radioactive Isotope mitchellmckain's Avatar
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    Quote Originally Posted by almirza
    hi friends,

    I think all of us know Newton's third law of motion and one of the applications of this kaw is our walking system
    when we push the earth the earth push us with same size of force forwards
    But what i want to ask , since the two forces are equal in size and opposite in direction and they are in the same line at the same time [color=red]SO WHY THE RESELTANT FORCE THAT MAKES US WALK IS NOT ZERO?
    The resultant force is adding up all the forces on one object but Newton's third law it talking about forces on two different objects. The force you exert on the earth is equal and opposite the force (the normal force) which the earth exerts on you. But the resultant force on you is the normal force plus gravity. These cancel when standing still, but the normal force exceeds gravity when you jump.
    See my physics of spaceflight simulator at http://www.relspace.astahost.com

    I now have a blog too: http://astahost.blogspot.com/
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