Scarf modelled as a pulley system / F=ma exercise

  • #1
laser
75
10
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
1701010123507.png


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?
 
Physics news on Phys.org
  • #2
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##.
 
  • Like
Likes laser
  • #3
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.
 
  • #4
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 … 🤔
 

1. How does a scarf modelled as a pulley system work?

A scarf modelled as a pulley system is a simple machine that uses a combination of fixed and movable pulleys to lift or move objects. The scarf acts as the rope in the pulley system, and when pulled, it creates a mechanical advantage by distributing the force needed to lift the object over multiple ropes and pulleys.

2. What is the formula for calculating the force in a scarf modelled as a pulley system?

The formula for calculating the force in a scarf modelled as a pulley system is F = ma, where F is the force applied to the scarf, m is the mass of the object being lifted, and a is the acceleration of the object. This formula is derived from Newton's second law of motion, which states that force is equal to mass times acceleration.

3. How can a scarf modelled as a pulley system be used to demonstrate Newton's laws of motion?

A scarf modelled as a pulley system can be used to demonstrate all three of Newton's laws of motion. The first law, also known as the law of inertia, can be shown by pulling the scarf with a constant force and observing the object's constant velocity. The second law can be demonstrated by varying the mass of the object being lifted and observing how it affects the force needed to lift it. The third law, or the law of action and reaction, can be shown by pulling the scarf in different directions and observing how the object moves in response.

4. What are the advantages of using a scarf modelled as a pulley system for the F=ma exercise?

One advantage of using a scarf modelled as a pulley system for the F=ma exercise is that it allows for a hands-on and visual demonstration of the concept. It also allows for easy manipulation of the variables, such as mass and force, to observe the effects on acceleration. Additionally, it is a low-cost and easily accessible tool for teaching and learning about Newton's laws of motion.

5. Are there any safety precautions to consider when using a scarf modelled as a pulley system?

Yes, there are a few safety precautions to consider when using a scarf modelled as a pulley system. It is important to ensure that the scarf is securely tied and that the pulleys are in good working condition. Additionally, it is recommended to use lightweight objects for the exercise to avoid any potential injuries. It is also important to supervise children when using the pulley system to ensure proper handling and prevent accidents.

Similar threads

  • Introductory Physics Homework Help
Replies
30
Views
1K
  • Introductory Physics Homework Help
Replies
15
Views
2K
  • Introductory Physics Homework Help
Replies
29
Views
923
  • Introductory Physics Homework Help
Replies
8
Views
6K
Replies
8
Views
9K
  • Introductory Physics Homework Help
Replies
8
Views
2K
  • Introductory Physics Homework Help
Replies
3
Views
1K
  • Introductory Physics Homework Help
2
Replies
66
Views
5K
Replies
37
Views
3K
  • Introductory Physics Homework Help
Replies
3
Views
984
Back
Top