Angle of the slope when the object start moving

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Homework Help Overview

The discussion revolves around the relationship between the angle of a slope and the motion of an object on that slope, specifically focusing on the angles at which static and kinetic friction apply. Participants are exploring the conditions under which an object begins to slide and how the angles associated with static and kinetic friction compare.

Discussion Character

  • Conceptual clarification, Assumption checking, Problem interpretation

Approaches and Questions Raised

  • Participants are questioning the relationship between the angles of static and kinetic friction, particularly why the angle when the object is moving is perceived to be larger than the angle when it is about to move. There are discussions about the nature of static versus kinetic friction and the implications of these forces on the motion of the object.

Discussion Status

The discussion is ongoing with various interpretations being explored. Some participants are providing insights into the behavior of friction at different angles, while others are seeking clarification on the definitions and implications of the angles involved. No explicit consensus has been reached, but there are productive exchanges regarding the mechanics of motion on slopes.

Contextual Notes

Participants are navigating the nuances of friction coefficients and the physical relevance of specific angles. There is an acknowledgment that the conditions of the problem may not align perfectly with theoretical models, as real-world scenarios often involve complexities not captured in simplified equations.

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Homework Statement


when the object is moving , why the theta is larger than the theta(s) when the object is started moving ?
I was told that when the object is moving , the Fk will become smaller than Fs , right ? so, IMO , the theta should be larger than the theta(s) , am i right ?

Homework Equations

The Attempt at a Solution


tan(theta k)= Fk / N = = μ k (N) / N
tan (theta s) =Fs / N = μ s (N ) / N
angle is directly proportional to μ k and μ s
 

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goldfish9776 said:
when the object is moving , why the theta is larger than the theta(s) when the object is started moving ?
They could have written >=, but the exact border case rarely has physical relevance - no slope is perfectly flat and so on.
goldfish9776 said:
I was told that when the object is moving , the Fk will become smaller than Fs , right ?
Sliding friction is usually smaller than static friction. Once the object starts moving, you can reduce the tilt angle and the object will continue sliding.
 
mfb said:
They could have written >=, but the exact border case rarely has physical relevance - no slope is perfectly flat and so on.
Sliding friction is usually smaller than static friction. Once the object starts moving, you can reduce the tilt angle and the object will continue sliding.
do u mean when the object is sliding , no matter the angle is larger than μ s or the angle is slightly smaller than μ s , the object will still sliding down the plane ?
 
μ s is not an angle.

There is an angle ##\theta_0## where the object starts sliding (it starts sliding for all angles larger than that, and does not start for all angles smaller than that). There is a different angle ##\theta_1 < \theta_0##, between those two angles an object that is sliding keeps sliding (forever), but won't start sliding on its own if it is at rest.
 
mfb said:
θ1<θ0
as you stated , why the book gave θ(when it's moving ) will bigger than θ(when it's about to move ) ?
 
The logic is in the other direction: if the angle is larger, it is certainly moving.
 
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