Does Friction Oppose Motion on an Inclined Surface?

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Discussion Overview

The discussion revolves around the nature of friction on an inclined surface, specifically whether friction opposes motion or acts in the same direction as the movement of an object. The scope includes conceptual clarification and technical explanation of friction's role in relation to motion.

Discussion Character

  • Conceptual clarification, Debate/contested

Main Points Raised

  • Some participants propose that friction should act in the same direction as the motion of an object on an inclined surface.
  • Others argue that friction always acts in the opposite direction to the direction of movement of the object.
  • A later reply clarifies that friction opposes the relative motion between the object and the underlying surface, suggesting that it seeks to equalize their motions.
  • One participant provides an example involving a brick dropped onto a moving plank to illustrate how friction can accelerate the brick in the direction of the plank's motion until they move together.
  • Several participants reiterate that friction opposes motion, emphasizing the concept of relative motion.

Areas of Agreement / Disagreement

Participants express differing views on the direction of friction in relation to motion, with no consensus reached on whether friction can act in the same direction as motion under certain conditions.

Contextual Notes

The discussion highlights the complexity of friction's behavior, particularly in relation to relative motion and the definitions of motion involved. Some assumptions about the conditions of motion and surface interactions remain unaddressed.

Nstraw
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If we Are moving an object on an inclined surface than shouldn't friction be in the same direction?
 
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Nstraw said:
If we Are moving an object on an inclined surface than shouldn't friction be in the same direction?
Same direction as what? The motion of the object?
 
Nstraw said:
If we Are moving an object on an inclined surface than shouldn't friction be in the same direction?

Friction is always in the opposite direction to the direction of movement of an object.
 
anjelin said:
Friction is always in the opposite direction to the direction of movement of an object.

Not exactly.
It opposes the RELATIVE motion the object has to say, the underlying surface.

That is:
Friction seeks to equalize the motions of the object and the surface.

Suppose you drop a brick (no horizontal velocity) onto a moving plank.
The friction from the plank will accelerate the brick in the direction of its own generated horizontal motion, until the brick moves with the same speed as the plank.
 
So friction will oppose the motion
 
Nstraw said:
So friction will oppose the motion

It opposes relative motion between the object and the surface.
 

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