Calculating Belt Length for Pulley Rotation

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Discussion Overview

The discussion revolves around calculating the length of a belt required to connect two pulleys of different diameters, specifically focusing on the geometry involved when the pulleys rotate in the same or opposite directions. The problem includes aspects of trigonometry and geometry, particularly in relation to the arrangement of the pulleys and the belt.

Discussion Character

  • Homework-related
  • Mathematical reasoning
  • Technical explanation

Main Points Raised

  • One participant expresses difficulty in starting the problem and seeks assistance.
  • Another participant suggests using trigonometry to find the hypotenuse, implying a geometric approach.
  • A participant mentions the need to draw a diagram of the pulleys and belt to visualize the problem.
  • There is a discussion about forming a right triangle by extending tangent lines from one pulley to the other, although uncertainty remains about calculating the belt's length around the pulleys.
  • One participant confirms that the length of the belt wrapping around the pulley can be considered as arc length.
  • Further clarification is provided that understanding the angle involved is necessary for calculating the arc length.

Areas of Agreement / Disagreement

Participants generally agree on the need for a geometric approach involving diagrams and trigonometry, but there remains uncertainty about specific calculations, particularly regarding the arc length and angles involved.

Contextual Notes

Participants have not resolved the specific mathematical steps needed to calculate the belt length, and there are assumptions about the geometry that have not been explicitly defined.

ur5pointos2sl
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A narrow belt is used to drive a 20.00-cm diameter pulley from a 35.00-cm-diameter pulley. The centers of the two pulleys are 2.000 m apart. How long must the belt be if the pulleys rotate in the same direction? In opposite directions?

I am sure the solution to this problem is very simple, but I just cannot seem to figure out how to even begin this problem.Any help would be appreciated.
 
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I think you just need to find the hypotenuse using trigonometry.
 
ur5pointos2sl said:
... I just cannot seem to figure out how to even begin this problem.

Solving this begins with drawing a picture of the wheels and belt.
 
Redbelly98 said:
Solving this begins with drawing a picture of the wheels and belt.

well of course that would be the obvious thing to do. Once i have it drawn I am guessing I need to form a right triangle? Simply by extending a tangent line from one pulley to the other on top and bottom? From here i am stuck. I know that the center is 2 cm but how do you calculate for the belt wrapping around the pulley itself? Would that be arc length or something?
 
Hi ur5pointos2sl! :smile:
ur5pointos2sl said:
… how do you calculate for the belt wrapping around the pulley itself? Would that be arc length or something?

Yes, that's arc-length! :smile:
 
ur5pointos2sl said:
well of course that would be the obvious thing to do.

Okay, guess I took you too literally when you said you didn't know how to begin.

Once i have it drawn I am guessing I need to form a right triangle? Simply by extending a tangent line from one pulley to the other on top and bottom? From here i am stuck. I know that the center is 2 cm but how do you calculate for the belt wrapping around the pulley itself? Would that be arc length or something?

Pretty much. Draw simple shapes like right triangles, rectangles, and/or circles to figure things out. Yes, the length of belt portion wrapping around the pulley is an arc length; you'll need to figure out the angle involved using geometry and trig.
 

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