Pushing force vs. Friction force

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SUMMARY

The discussion clarifies the relationship between pushing force and friction force in mechanics. When an object moves at a constant velocity, the pushing force (F) equals the friction force (Fr), resulting in F = Fr. The misconception arises from confusing zero net force with zero velocity; a net force of zero indicates constant velocity, not necessarily at rest. Once the pushing force exceeds friction, the object accelerates until both forces balance, leading to constant velocity.

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RobinSky
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My teacher in mechanics says that when we have a force pushing an object (moving at constant velocity) forward we also have a friction force that equals to the force that is pushing the object. So if we call the friction force for Fr and the pushing force for F, F=Fr.

But in my mind, when we have 2 forces in opposite directions the object is standing still. So if my teacher is correct, how am I thinking wrong? Or can any give some tips to solve this fault of thinking.

Regards, Robin Andersson
 
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RobinSky said:
But in my mind, when we have 2 forces in opposite directions the object is standing still.
Your teacher is correct. Your error is in thinking that a net force of zero implies zero velocity. What it does imply is zero acceleration. If the net force is zero, then the velocity will be constant, not necessarily zero.
 
In other words, once the pushing force exceeds the force of friction, the object accelerates from rest until the friction force and pushing force are equal...from then on constant velocity ensues.
 

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