# Help understanding dynamic equilibrium

#### urbano

1. The problem statement, all variables and given/known data

if the equilibrium rule states ƩF=0N, how can something move or be moving at a constant speed ? eg I push on a box with 50N and friction provides 50N back, resulting in ƩF=0N. So I am not providing more N than the box is resisting with. I thought something could only be moved if the moving force was greater than the resisting force ? otherwise wouldn't it be a stand still ?
2. Relevant equations

3. The attempt at a solution

****update*****

just had thought...I'd only need more force than the friction provided to get the box moving, but once moving and if at a constant speed then its motion is unchanged, thus the zero net force ?? And this then becomes the first law as now it is moving it will remain moving until an unbalanced force acts upon it ??

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#### gneill

Mentor
Newton's first law. If the ƩF=0N, no change in motion occurs.

#### aftershock

What if the box is sliding on the table by itself and there's no friction?

#### gneill

Mentor
What if the box is sliding on the table by itself and there's no friction?
If there's no friction, what's the net force acting?

#### aftershock

If there's no friction, what's the net force acting?
That was directed at the OP, in hopes of him being able to figure out the answer to his question.

#### gneill

Mentor
That was directed at the OP, in hopes of him being able to figure out the answer to his question.
Ah. Sorry for pouncing then #### urbano

What if the box is sliding on the table by itself and there's no friction?
hmmm I dont quite get what would make the box slide ? If ƩF=0 and there's no friction my guess would be there is no force...but then I don't get how the box would be sliding with no force on it

#### gneill

Mentor
hmmm I dont quite get what would make the box slide ? If ƩF=0 and there's no friction my guess would be there is no force...but then I don't get how the box would be sliding with no force on it
What if it were already sliding?

Motion does not require a force. Only a change in motion requires a force.

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