Block on Inclined Plane: The Effects of a Fixed vs. Unfixed Surface

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Discussion Overview

The discussion revolves around the dynamics of a block sliding down an inclined plane, specifically comparing scenarios where the inclined plane is fixed versus unfixed. Participants explore the implications of the inclined plane's movement on the forces acting on the block and the plane itself, incorporating concepts from Newton's laws and friction.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants propose that the effects on the block's motion would be the same whether the inclined plane is fixed or not.
  • Others argue that the inclined plane exerts a force on the block, and this interaction is crucial to understanding the system's behavior.
  • A participant suggests that the movement of the inclined plane will depend on the mass of both the block and the plane, as well as the coefficient of friction between the surfaces.
  • Some participants discuss the normal force exerted by the inclined plane on the block, noting that it equals mgcosθ only if the plane does not accelerate.
  • There is a suggestion to analyze the situation using a free body diagram to clarify the forces at play.
  • One participant expresses uncertainty about the direction of the inclined plane's movement if it were to slide, despite agreeing that the block exerts a force on the plane.
  • Another participant mentions that conservation of momentum applies to the scenario, indicating a more complex interaction between the block and the inclined plane.

Areas of Agreement / Disagreement

Participants do not reach a consensus on whether the effects of the block's motion would be the same for fixed and unfixed inclined planes. Multiple competing views remain regarding the forces involved and the resultant motion of the inclined plane.

Contextual Notes

Participants highlight the importance of considering the mass and friction in their analyses, as well as the conditions under which the normal force is defined. There are unresolved aspects regarding the direction of motion of the inclined plane and the implications of different frictional scenarios.

konichiwa2x
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Hi,
I recently did a problem in which a block of definite mass was placed on the top of a inclined plane which was inclined at some angle with the horizontal. The block starts to slide down. What would happen if the inclined plane was not fixed?
 
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konichiwa2x said:
Hi,
I recently did a problem in which a block of definite mass was placed on the top of a inclined plane which was inclined at some angle with the horizontal. The block starts to slide down. What would happen if the inclined plane was not fixed?
What do yo think would happen?
 
well I think there won't be any effect i.e, it would be the same as if it was fixed. is that right?
 
No. Answer this question: Does the inclined plane exert a force on the block?

Then consider Newton's 3rd law.
 
The movement(s) will depend on the mass of the block and plane, and the coefficient of friction between block/plane and plane/floor.

Imagine what would happen if you had a 50 lb block of ice on a 10 lb 45 degree metal plane on a sheet of ice.
 
No. Answer this question: Does the inclined plane exert a force on the block?

Then consider Newton's 3rd law.

yes , mgcos[tex]\theta[/tex] if [tex]\theta[/tex] is the inclination of the inclined planed with respect to the horizontal. So that means the block also exerts a force equal in magnitude on the inc. plane. I think if the magnitude of this force is large enough, the inclined plane will move . But I am not sure in which direction. Is this correct?
 
konichiwa2x said:
yes , mgcos[tex]\theta[/tex] if [tex]\theta[/tex] is the inclination of the inclined planed with respect to the horizontal. So that means the block also exerts a force equal in magnitude on the inc. plane. I think if the magnitude of this force is large enough, the inclined plane will move . But I am not sure in which direction. Is this correct?
Yes, this is correct. Try drawing a free body diagram and examine the forces. You may also wish to note that conservation of momentum applies here.
 
konichiwa2x said:
yes , mgcos[tex]\theta[/tex] if [tex]\theta[/tex] is the inclination of the inclined planed with respect to the horizontal.
Careful. The force that the incline plane exerts on the block--the normal force--will only equal [itex]mg\cos\theta[/itex] if the plane does not accelerate.
So that means the block also exerts a force equal in magnitude on the inc. plane.
Yes, that is exactly the point.
I think if the magnitude of this force is large enough, the inclined plane will move . But I am not sure in which direction. Is this correct?
Yes. A simple case to analyze is when the inclined plane slides without friction.

The direction that the inclined plane will move is easy to determine. The only horizontal force on the plane is the normal force exerted by the block on the plane. If you draw a diagram showing the forces acting (as Hoot suggests) you will quickly see which way that force acts.
 

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