Friction Forces Between Stacked Blocks: Determining Direction

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SUMMARY

The discussion focuses on determining the direction of friction forces between stacked blocks in a physics problem. When a heavier block is pulled to the right, the top block experiences friction to the right, while the bottom block experiences friction to the left. This is due to the difference in acceleration between the two blocks, where the bottom block accelerates faster than the top block, causing the top block to fall off the left side. The key takeaway is that the friction force on the top block acts in the direction of the applied force, while the bottom block's friction force acts in the opposite direction.

PREREQUISITES
  • Understanding of Newton's Second Law (F = ma)
  • Familiarity with Free Body Diagrams (FBD)
  • Basic concepts of friction and acceleration
  • Knowledge of relative motion between objects
NEXT STEPS
  • Study the effects of friction on stacked objects in different acceleration scenarios
  • Learn about Free Body Diagram techniques for complex systems
  • Explore Newton's Laws of Motion in practical applications
  • Investigate the role of static and kinetic friction in real-world examples
USEFUL FOR

Students studying physics, educators teaching mechanics, and anyone interested in understanding the dynamics of friction in multi-body systems.

minimario
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Homework Statement



UWQB18J.png

Homework Equations



F = ma

The Attempt at a Solution



When drawing a FBD for block 1, I couldn't figure out if the friction force between the blocks was toward the left or toward the right. Similar situation on block 2. How would I determine this?
 
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Which direction do you expect for the acceleration of the top block?

Technically you can choose both directions for the force, but one choice will give a negative value for the force.
 
Accelerate left. So the friction force would be left?
 
Which way do the dishes accelerate in this video?
 
To the right, but when I put a book on top of a heavier book and pull the heavier book right, the book goes left and falls off?
 
minimario said:
To the right, but when I put a book on top of a heavier book and pull the heavier book right, the book goes left and falls off?
No, the top book goes right. It falls off the left end of the bottom book because the bottom book accelerates faster than the top book.
 
Oh. So the friction on the top book would be right, and that on the bottom book would be left.
 
minimario said:
Oh. So the friction on the top book would be right, and that on the bottom book would be left.
Yes, that's correct.
 

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