Scarf modelled as a pulley system / F=ma exercise

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Homework Help Overview

The discussion revolves around a physics problem involving a scarf modeled as a pulley system, specifically focusing on the relationship between two masses, m1 and m2, and the proportion of the scarf hanging over the edge. The subject area includes concepts from mechanics and ratios in physics.

Discussion Character

  • Conceptual clarification, Assumption checking

Approaches and Questions Raised

  • Participants are questioning the validity of the proportion $$\frac{m_1}{m_1+m_2}$$ and its implications when comparing the masses m1 and m2. There is a discussion about intuition versus mathematical definition regarding the expected size of the proportion under different mass conditions.

Discussion Status

The conversation is exploring differing interpretations of the proportion and its expected behavior based on the relative sizes of m1 and m2. Some participants are providing clarifications about the definition of the ratio, while others express confusion about the implications of their intuition.

Contextual Notes

Participants are grappling with the assumptions related to the behavior of the system when one mass is significantly larger or smaller than the other, and how this affects the proportion of the scarf. There is an acknowledgment that the proportion cannot exceed 1, which is a point of contention in the discussion.

laser
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Homework Statement
Consider a scarf draped over a table. Model it as two particles of mass m1 and m2 joined by a model string passing over the edges of the table modelled as a model pulley. Assume the masses are proportional to the corresponding lengths of the scarf, i.e. the scarf’s mass is uniformly distributed. If the coefficient of static friction between the scarf and the table surface is μ, what proportion of the scarf can hang over the table before the scarf slips off the table?
Relevant Equations
F=ma
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My teacher gave the above answer as a solution. However, I am not convinced that the proportion is really $$\frac{m_1}{m_1+m2}$$. If m2 << m1the proportion would be really big, right? But intuition tells me that it should be the opposite. Furthermore, if m2 >> m1, then one would expect the proportion to be "big". But it's the opposite :/.

What am I missing here?
 
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The ratio ##m_1/(m_1+m_2)## is by definition the proportion of the scarf hanging over the edge. Since ##m_1## is the mass hanging over the edge, this should be expected to be large whenever ##m_1 \gg m_2##.
 
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laser said:
If m2 << m1the proportion would be really big, right? But intuition tells me that it should be the opposite. Furthermore, if m2 >> m1, then one would expect the proportion to be "big". But it's the opposite :/.
Intuition is telling you the same thing for both m2>>m1 and m2<<m1, yet is wrong both times? That does not sound possible.
Besides, it can never be "really big". It clearly cannot exceed 1.
 
haruspex said:
Besides, it can never be "really big". It clearly cannot exceed 1.
I’d say 1 is a “really big” fraction of the scarf … it is all of it … 🤔
 

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