Incline Forces: Understanding Block Movement on an Inclined Plane

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Discussion Overview

The discussion revolves around the conditions that determine the movement of a block on an inclined plane when connected to a hanging mass via a pulley system. Participants explore the forces at play, including gravitational forces and friction, in a frictionless context.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions whether the direction of the block's movement is determined by the horizontal weight force of the box and the gravitational force of the hanging weight.
  • Another participant identifies three components of force to consider: the gravitational force parallel to the incline, the spring force (though later clarified as a string), and the frictional force, which is proportional to the normal component of the box's weight.
  • A participant emphasizes the importance of all variables, including the coefficient of friction, although later clarifies that the scenario is frictionless.
  • A follow-up question asks if the heavier mass determines the direction of movement when the mass on the incline is released.
  • One participant corrects their earlier misunderstanding about the forces involved and states that the heavier mass alone does not determine the direction of movement, suggesting that the incline's angle is a critical factor.
  • Another participant proposes considering the two masses as a single system, indicating that the greater force acting on the system will dictate the direction of movement.

Areas of Agreement / Disagreement

Participants express varying views on the factors influencing the block's movement, with no consensus reached on a definitive answer. The discussion remains unresolved regarding the interplay of forces and their effects on movement.

Contextual Notes

The discussion assumes a frictionless incline but does not resolve the implications of this assumption on the forces involved. There are also unresolved aspects regarding the definitions and roles of the forces mentioned.

ixbethxi
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i just was wondering, when you have an incline and a box mass m sits on it attached to a massless string and a pulley and a weight hanging freely. what determines whether the block will slide up or down the ramp?

is it the horizontal weight force for the box and the force of gravity for the weight?
 
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You have three components of force to consider: (a) the component of the weight (graviational force) parallel to the surface, (b) the component of the spring force parallel to the surface and (c) the frictional force (parallel to the surface) between the box and the incline which is proportional to the component of the box's weight normal to the surface.
 
All the variables matter - and don't forget the coefficient of friction...
 
oo i forgot to say its frictionless ;)
 
i mean let's say you are holding the mass on the incline still and then you let go, does the mass that's heavier determine if the mass on the incline will make it slide up or down?
 
Yikes! I misread your original post - thought it said spring instead of string!

No, it's not the heavier mass (alone) that determines which way it moves. Consider the limit of the incline being 0! Then no matter how massive the object on the incline is it will move toward the suspended mass.

All you have to do is compare the components of force along (parallel) to the plane.
 
Consider the two connected masses as a single system. Gravity pulls each end:
(1) The hanging mass end is being pulled down with a force [itex]m_1 g[/itex]
(2) The mass on the incline is being pulled down the incline with a force [itex]m_2 g \sin \theta[/itex]​
The greater of those two forces will determine which way the system moves.
 

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