Why Is the Normal Force on the Pulley Not Parallel to Gravity?

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SUMMARY

The discussion centers on the mechanics of a system involving a box, a pulley, and a rolling cylinder, each with mass M and specific radii. The normal force on the pulley is not parallel to gravity due to the tension in the string exerting a horizontal force, requiring the pulley to exert a counteracting force. Key equations include Στ=Iα, τ=RFsin(θ), and ΣF=ma, which are essential for analyzing the forces and torques in the system. Understanding the relationship between linear and angular accelerations is crucial for solving the problem.

PREREQUISITES
  • Understanding of Newton's laws of motion
  • Familiarity with free-body diagrams
  • Knowledge of rotational dynamics, specifically torque and moment of inertia
  • Basic concepts of linear and angular acceleration relationships
NEXT STEPS
  • Study the derivation of free-body diagrams for pulley systems
  • Learn about the relationship between linear and angular motion in rotating systems
  • Explore the implications of tension in strings on pulley mechanics
  • Investigate advanced topics in rotational dynamics, including the effects of friction on pulleys
USEFUL FOR

This discussion is beneficial for physics students, educators, and anyone studying mechanics, particularly those focusing on pulley systems and rotational dynamics.

zippeh
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Homework Statement


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Let’s have one box, one pulley, and one rolling cylinder. Each of them have mass M, the pulley’s radius is R, and the cylinder’s radius is 2R. Consider the cylinder to be rotating about its center of mass. (a) Draw correct and complete free-body diagrams. (b) Give the equation(s) that come from the free-body diagrams (there are at least 7 equations). (c) Also give the equations that relate the various accelerations to each other (there are at least 4 linear and angular accelerations to consider). You do not need to solve for anything.

Homework Equations


Στ=Iα
τ=RFsin(θ)
ΣF=ma

The Attempt at a Solution


l5pulley.jpg

[/B]
I am just confused on the portion of the normal force of the pulley. I included the above photo to demonstrate what I mean. I guess I don't completely understand why the normal force is not parallel to the gravity. It makes sense that it isn't because the T from the cylinder would be equal to 0 (T=Ma -> T=O). I am just confused. Then I guess I am confused on how to compare the accelerations together. Thanks!
 
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zippeh said:
I don't completely understand why the normal force is not parallel to the gravity
For exactly the reason you give. Since the horizontal section of string is tending to push the pulley left, the pulley mounting must resist this by exerting a force to the right.
 

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