Hanging clothes on a windy day

Question

Hanging clothes on a windy day can be really challenging, especially if you don't have any clips lying around. Today I was hanging the clothes out in the drying area of my hostel. But soon, it turned out that today was a heck of a windy day. It's monsoon, and rarely does one get a clear sky and a hot sun like there was today. So today, I was mostly experimenting with the various configurations of hanging clothes to find which is most resistant to wind.

Though most of my experiments have failed, and I have to rewash my clothes, at least now I know what to say when someone asks me which is the optimal configuration to hang clothes on a rope :).

I classified my clothes into two broad categories.

• Symmetric: bath towels, bedsheets, etc.
• Asymmetric: shirts, pants, T-shirts, shorts, etc.

For all symmetric clothes, I found that the best way of hanging them was in such a way that they are distributed equally on both sides, as one would expect.

But for asymmetric clothes, the answer was not so trivial.

Let's take my t-shirt for example.

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There are 6 configurations possible for hanging a t-shirt (not considering the ones that take up too much space on the rope).

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For all of the illustrations above, the wind flow is such that the clothes fly out from the screen towards you. I must also mention that our drying area lies in a pocket between two buildings, so the wind always flows in one direction.

• I learned that the most stable configuration is the one shown in B3.
• I also learned that A3 and B1 are the worst possible configurations.

This also applies to other asymmetric clothes.

TL;DR, for symmetric clothes, its best to hang them by keeping both sides spread equally (as in A2). And for asymmetric clothes, hang the cloth such that the heavier side is raised up and the lighter side is lowered down (as in B3).

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How would you explain these observations? Why is the B3 configuration more stable than A1, even though they look very similar?

Short and to the point anwers are welcome.

Answer 1

T-shirts are non-uniform objects. The part above the chest of the t-shirt weighs more than its belly. Therefore, when you hang one of them on a rope, one side of the shirt will likely be less heavy than the other side (there is a net force).

If there were no friction, the shirt would've fallen due to its own gravity (of course, this doesn’t happen due to the friction at the point of contact of the shirt and the rope). Now the wind is like a random destabilizing agent, and if you have any imbalanced forces in your T-shirt system, ultimately, the system would go where it wants to go.

So the first thing we need to do to hang our t-shirt is to balance the weight of both sides. So [A1, B3] are good configurations, [A2, B2] are ok, but [A3, B1] are just bad. So, which is the best among A1 and B3?

Now the resistance of the cloth against wind solely depends on how hard its 'clutch' is on the rope. There are two main forces involved in this clutching.

1. The friction acting at the point of contact of cloth and the rope.
2. The friction acting between the two sides of the T-shirt.

Friction at point of contact depends on the contact angle of the shirt with the rope. When the contact angle is small, friction is large and the shirt doesn’t fall. When the angle is large, friction is small and the shirt slips down from the rope. And the friction between the two sides of the T-shirt depends on how hard both are pressed together (normal reaction).

In both A1 and B3, the shirt’s belly catches the wind better (because it has more surface area) and gets raised up.

In A1 (where the belly is free to move), this will widen the gap between the sides, increasing the contact angle, weakening the clutch of the shirt on the rope.

Front view

Side view

Notice the belly flowing freely away from the chest, weakening the clutch.

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Whereas in B3, as the contact angle is lowered, there is no such weakening like before. Since the chest is resting on the belly, the clutch is actually strengthened due to the added friction between the chest and belly.

Front view

Side view

Notice the chest resting on the belly, reinforcing the clutch.

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So we have a winner, and it's indeed B3 :).

To conclude, irrespective of the shape of the cloth, the best way to hang them would be to balance them on both sides, and then orient them in such a way that the larger side faces the wind.