Actio = Re...qulibrium? The Difference between Newton's third axiom and a force equilibrium

in education •  7 years ago  (edited)

For those who are curious I'll try to explain here where the difference lies between
Newton's third axiom or law (actio =reactio)and a system that's in a equilibrium or balance of force.

First of all: Yes one could argue, that Anakin brought balance to the force by, the of course very reasonable and not totally insane thing of, slaying almost the entire Jedi-order evening the numbers between Sith and Jedi, but that's not our topic...today at least.

The players:

  • Newton's third axiom: Brought to you by the guy who discovered gravity and lend his name to the philosophical principle of NEWTOWNS FLAMING LASERSWORD...okay maybe it's a bit about star wars. Anyway.
    Newton's third axiom states that "To every action there is always opposed an equal reaction".
    Meaning: If you push with your finger against a wall your finger is pushed in by the exact same amount of force, but of course in the opposite direction. If that wasn't the case your finger would be stretched, I think we can all agree that this would not only look ridiculous but also would be a rather unexpected event. Your finger stretching when you push something.
    We can quite nicely observe this effect, you can do it at home if you want.
    Imagine you and your buddy Ocean, who somehow convinced you to stand on a skateboard with a rope in hand while he does the same thing. He then starts pulling himself towards you and you notice that you also start to move even though you're just holding the rope and as the skateboards meet in the middle he pushes you away.
    And again you both start to move in opposite directions...at the same speed...just like before where you were moving towards each other and you notice that moving towards each other is also moving in the opposite direction.
    So whether he pulls or pushes it always results in you going at the same speed in the opposite direction.
    Maybe that weird 18th century dude with the fancy hair was onto something.
    But...if we move in the opposite direction at the same speed, why do the forces that act on us not erase each other?

  • The Equilibrium of Forces:
    Equilibrium is not only an excellent German folk metal band, but also means the following.
    When you have two (of course an number of forces is okay, but we'll stick with two for the example) pointing in opposite directions with the same amount of force, nothing happens. This seems rather obvious and it is. It's such a basic concept we made a whole game about this principle! Tug of war.

So where exactly is the difference?
What you may have noticed is that you and your buddy Ocean are two different persons, but the rope in tug of war is only one...ehm...ähh...person. And the key here is in the numbers 1 &2.
In the case of newton's third law it is always about one object exerting a force onto another object resulting in the same force being exerted onto the first object. It is elementary my dear Watson that this is the case, because if you think about it should and can not make a difference to the resulting movement whether you or your buddy Ocean is pulling the rope.
An equilibrium of forces only ever refers to one single object.
Of course multiple objects can be in an equilibrium with each other when they exert force onto each other, but also this results in the overall system (every object counted together) not moving and therefore being in balance.

I hope that this was understandable language wise (English is not my first language) or you didn't understand the content just let me know.
I'm happy to answer any questions.

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