[Guest]

If, according to newton, every action has an equal and opposite reaction, how can anything move? If you tried to walk, you would be transfixed by the fowards motion and backwards reaction! But this is obviously wrong, because we can walk. But thousands of other scientists have done experiments proving Newton right! So what should we believe: scientific process, or personal experience?

Not really a paradox, but the best i can do.

[Guest]

If, according to newton, every action has an equal and opposite reaction, how can anything move? If you tried to walk, you would be transfixed by the fowards motion and backwards reaction! But this is obviously wrong, because we can walk. But thousands of other scientists have done experiments proving Newton right! So what should we believe: scientific process, or personal experience?

Not really a paradox, but the best i can do.

Your forward motion is a reaction to the action of your muscles working. The resulting action displaces the environment around you (air, water, whatever medium you happen to be in) as well as the application of forces in many directions, including down. The math all equals zero. At least that's what a civil engineer told me.

Hmmm, that sounded a bit awkward. Maybe someone with a clearer and more learned point of view can fill in the blanks?

[Guest]

...according 2 my daddy Grayven is about right...

[unreality]

when you first learn this in physics, you (should have) also learned that the action/reaction force pairs act on different objects.

[Guest]

Shouldn't this be in the "paradoxes" topic area??????

:roll:

[Guest]

An example that applies directly to your statement in the OP, when you walk your foot drags backwards on the earth, and you push forward against the air. These aren't the opposing forces, though. Your foot drags backwards against the earth, thereby pushing the earth backwards, and the earth pushes forward on your foot, thereby causing you to walk. However, the force you apply to the earth isn't enough to move it very far, so you don't notice the earth moving. The same is true for the air particles. You push forward on them, and other things push on them from the other side as they attempt to move, but since the air weighs so much less than you, the effect you have on it is to cause it to part around you, and the effect it has on you is negligible.

[Yoruichi-san]

An example that applies directly to your statement in the OP, when you walk your foot drags backwards on the earth, and you push forward against the air. These aren't the opposing forces, though. Your foot drags backwards against the earth, thereby pushing the earth backwards, and the earth pushes forward on your foot, thereby causing you to walk. However, the force you apply to the earth isn't enough to move it very far, so you don't notice the earth moving. The same is true for the air particles. You push forward on them, and other things push on them from the other side as they attempt to move, but since the air weighs so much less than you, the effect you have on it is to cause it to part around you, and the effect it has on you is negligible.

This is a good explanation. To put it slightly more mathematically, keeping to Newtonian physics, the 'equal' means that the force you apply to the earth is equal to the force the earth applies to you. Using Newton's first law, force=mass*acceleration, since the forces are equal, this means mass(you)*acceleration(you)=mass(earth)*acceleration(earth) => a(earth)/a(you) = m(you)/m(earth) ~ 10^(-23)

But actually...

was wrong ;P. Well, Newtonian physics work as an accurate predictor for the macroscopic world at non-relativistic speeds, but that's only b/c the relativistic terms vanish at that level. Quantum physics was invented/discovered to resolve the problems that were discovered when Newtonian physics was applied to microscopic level phenomenon.

[Guest]

Right. It's Newton's Third Law of Motion:

"Whenever a particle A exerts a force on another particle B, B simultaneously exerts a force on A with the same magnitude in the opposite direction. The strong form of the law further postulates that these two forces act along the same line. This law is often simplified into the sentence, "To every action there is an equal and opposite reaction." (Wikpipedia.)

OR:

"Forces always occur in pairs. If object A exerts a force F on object B,

then object B exerts an equal and opposite force –F on object A"

Yoruichi-san is of curse correct that this only applies in the "macro" (non quantum) sphere.

[Guest]

Interesting views, I'd have to agree this is largely force. Person walking initially deals with the force of gravity, a vector flag pointing to the earth. We then have the forward leaning for equilibrium and the upward vector of thrust from calf and foot muscles equal and opposite to gravity otherwise you won't move. The kinetics of motion and the force vectors from heal to toes ankle to tibia and fibula to knee to.. you get the point. All force vectors equal and opposite to gravity and the force leaning forward against wind vectors opposing the motion. All actions will create a vector of force in a direction where we would have equal and opposite vectors of force which cancel each other out satisfying Newton's law. Newton's paradox lies in the thought of walking. Our brain operates in chemistry and our synaptic cleft is a wonderful example of non force with electrical and chemical balance and imbalance where they are not equal and opposite they are transcendent.