Which of the two is the reason a block slides down a wedge?

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Discussion Overview

The discussion centers around the mechanics of a block sliding down an inclined plane, specifically examining the reasons behind the motion. Participants explore the roles of the normal force and gravitational components in this context, engaging in both conceptual reasoning and clarification of forces involved.

Discussion Character

  • Conceptual clarification
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • Some participants propose that the block slides due to the resultant of the normal force and gravitational force acting along the plane.
  • Others argue that it is specifically the component of gravitational force parallel to the plane, represented as mgsin(theta), that causes the sliding motion.
  • A few participants assert that both explanations are equivalent, although this claim is questioned by others.
  • There is a discussion about the cancellation of forces, with some noting that the normal force and the perpendicular component of gravity are equal and opposite, resulting in a net force of zero in that direction.
  • One participant suggests that only one of the force representations (N + mg or the resultant) should be considered at a time, rather than both simultaneously.

Areas of Agreement / Disagreement

Participants express differing views on whether the sliding motion is due to the resultant of forces or the specific gravitational component. There is no consensus on the equivalence of the two explanations, and the discussion remains unresolved regarding the interpretation of the forces involved.

Contextual Notes

Some participants express uncertainty about the mechanics involved, indicating a potential lack of clarity in understanding the forces acting on the block. The discussion also highlights the complexity of resolving the interactions between the normal force and gravitational components.

EddiePhys
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Is the reason the block slides down the plane that the resultant of the normal force N and mg acts along the plane causing it to slide or is it because of the component of mg parallel to the plane acting on the box i.e. mgsin(theta)
 
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Both are the same thing.
 
jbriggs444 said:
Both are the same thing.

Wait, what? How?
 
jbriggs444 said:
Both are the same thing.
Isn't N canceled out by mgcos(x)?
 
But both N and the component of gravity perpendicular to the slope are perpendicular to the slope.
 
jbriggs444 said:
But both N and the component of gravity perpendicular to the slope are perpendicular to the slope.
But in opposite directions, isn't it?

Pardon me but my mechanics suck
 
Right. They are in opposite directions and are equal. They add to a net of zero. All that is left after you add normal force plus gravity is the component of gravity parallel to the slope.

The resultant of normal force plus gravity is equal to mg sin theta.
 
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jbriggs444 said:
Right. They are in opposite directions and are equal. They add to a net of zero. All that is left after you add normal force plus gravity is the component of gravity parallel to the slope.

The resultant of normal force plus gravity is equal to mg sin theta.

Oh, I see. Thanks!
 
Perhaps make your drawing like this...

FBu5G.png
 
  • #10
Just to clarify, you do not have 3 forces acting on the block.
You can consider N + mg to be acting, or the resultant to be acting, but not both.
 
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