Help with frictional force concept

AI Thread Summary
Friction does not immediately stop an object after an applied force because it acts gradually to reduce momentum. When an object is in motion, it continues moving until friction overcomes its momentum, leading to a gradual halt rather than an immediate stop. The kinetic friction force remains constant as long as the normal force and contact surfaces do not change, and it does negative work until the object stops. If no external force is applied, the object would continue moving indefinitely due to Newton's first law. Ultimately, friction plays a crucial role in decelerating objects over a measurable time frame.
Jetview
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Salutations everyone!

I'm sure this is a simple question for many of you, but I don't understand why doesn't the force of friction immediately stop an object after an applied force? And for an instance when an object is moving and eventually comes to a halt, was it because the force of friction increased or the applied force gradually decreased to a point the object is stopped by the bigger frictional force??
 
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The kinetic friction force is determined by the normal to the contact surface and the kinetic friction coefficient.The friction is constant if the normal or contact surfaces do not change.If the kinetic friction force is greater then the other force on the object it will do negative work on the object until it stops.At that point we no longer talk about kinetic but by the static friction force which is now equal to the sum of the other forces on the object but smaller then the max fs.
 
Force never stops an object "immediately". Force accelerates (or decelerates) an object at a certain rate, depending on its mass.

If there was no friction, the object would just keep on moving forever after we stop applying force to it. Because there is friction, the object slows down and eventually stops. But this always takes a finite time. Even if it looks immediate for some very light objects, it still takes a measurabe amount of time.
 
Welcome to PF!

Salutations Jetview! Welcome to PF! :smile:
Jetview said:
… why doesn't the force of friction immediately stop an object after an applied force? … or the applied force gradually decreased to a point the object is stopped by the bigger frictional force??

I think you're confused about applied forces.

When friction reduces something to a halt, there's usually no applied force …

with no force, it will carry on at the same speed forever (good ol' Newton's first law) …

the friction reduces its momentum slowly and steadily to zero.

If there is an applied force (eg from an engine), that applied forces is usually constant, and so is the friction, so the acceleration (which may be negative) is also constant.​
 

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