S.O.S. Mathematics CyberBoard

Could someone explain the link between Newton’s second law and third law

when it comes to finding the resultant force?

Thanks.

What do you mean? and if you know the initial conditions, that just means the total force sum is the same as the initial forces. (which are usually 0).

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Let me give an example so i can better understand.

Lets say I hold pen in my hand and hold it up and keep it stationary. Newton's third law operates. :gravity force = reaction force of my hand

Now lets say I raise my hand. What happens to Newton’s Third law now that we have second law operating?

Nothing "happens", as you push up it pushes down more than it did at rest.

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No! That is not Newton's third law. Newton's third law says the gravitational forcing pulling down on the pen by the Earth is equal to the gravitational force pulling the Earth up to the pen by the pen. Also, the reaction force of your hand on the pen equal to the reaction force of the pen on your hand. Newton's third law does not assert equality of the the reaction and gravitational forces. For that, look at Newton's first law instead.

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When you say"the Earth is equal to the gravitational force pulling the Earth up to the pen by the pen", is this equal in magnitude to the "the reaction force of your hand on the pen"? Thanks.

How can the Earth be equal to a force pulling it? They're not the same thing, the sentence you wrote is nonsense as-written.

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