Help with frictional force concept

Click For Summary

Discussion Overview

The discussion revolves around the concept of frictional force and its role in stopping a moving object. Participants explore the relationship between applied forces and friction, particularly in the context of how friction affects motion over time.

Discussion Character

  • Conceptual clarification
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions why friction does not immediately stop an object when an applied force is removed, suggesting a misunderstanding of the dynamics involved.
  • Another participant explains that kinetic friction is constant under certain conditions and does negative work on the object until it stops, transitioning to static friction at that point.
  • A different viewpoint emphasizes that force does not stop an object immediately, as it accelerates or decelerates at a rate dependent on mass, and that friction causes the object to slow down over a measurable time.
  • One participant suggests that when friction brings an object to a halt, there is typically no applied force acting on it, and that friction gradually reduces momentum to zero.
  • Another participant notes that if an applied force is present, it is usually constant alongside friction, resulting in a constant acceleration, which may be negative.

Areas of Agreement / Disagreement

Participants express differing views on the mechanics of friction and applied forces, indicating that multiple competing perspectives remain without a clear consensus.

Contextual Notes

Some assumptions about the nature of forces and motion are not fully explored, such as the conditions under which friction acts and the specifics of applied forces in various scenarios.

Jetview
Messages
1
Reaction score
0
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??
 
Physics news on Phys.org
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.​
 

Similar threads

High School Are frictional forces action forces or reaction forces?
  • · Replies 14 ·
Replies
14
Views
2K
High School What Happens When The Applied Force Equals the Static Friction Force?
  • · Replies 2 ·
Replies
2
Views
4K
High School Need help understanding some concepts about friction
  • · Replies 12 ·
Replies
12
Views
2K
Undergrad Need help in understanding friction
  • · Replies 10 ·
Replies
10
Views
2K
High School Rolling of non-deforming sphere on a non-deforming rough surface?
  • · Replies 4 ·
Replies
4
Views
2K
High School Why is static friction necessary for pure rolling?
  • · Replies 4 ·
Replies
4
Views
3K
High School Questions about momentum and force as well as normal force/friction
  • · Replies 35 ·
2
Replies
35
Views
5K
High School Equivalence of Frictional and Applied Force
  • · Replies 2 ·
Replies
2
Views
2K
High School Why does friction decrease with repeated force application?
  • · Replies 11 ·
Replies
11
Views
3K
High School The power output of a vehicle when descending hills
  • · Replies 29 ·
Replies
29
Views
2K