Woolen sweaters shrink after washing. If a sheep is caught in the rain, will it be strangled to death by the wool?

I believe everyone has had this experience: a good wool sweater is thrown into the washing machine, and when you take it out, it has shrunk! It has become shorter! It can't be worn anymore!

It is said that wool comes from sheep. Pure wool sweaters will shrink after washing. So will the pure wool of sheep shrink after being exposed to rain?

Minute Earth, a science blogger on YouTube, made a video to explain why sheep don't get nervous because of the rain.

Like all mammalian hair, the outer layer of wool is surrounded by overlapping, oriented scales that make it easier for the wool to slide in a single direction.

The same is true for human hair:

Photo | ebena.net

It may be a bit abstract to imagine it alone, but you can try it yourself: pinch a hair with your fingers and slide it along the growth direction, which will be much smoother than sliding it towards the root direction. This is your hair scales at work.

This allows only one direction of motion, just like a ratchet (a special type of gear):

Figure | Mechanical Aesthetics

Or, have you ever used this kind of binding tape?

It's the same principle that you can enter but not exit.

This unidirectional frictional resistance occurs when a wool sweater is thrown into a washing machine and tumbled back and forth. When the wool fibers rub against each other, the scales act like little ratchets, allowing the fibers to move in only one direction:

After soaking in water, the situation becomes even worse. First, the fibers expand, making the contact between the fibers closer; second, the water softens the scales, making it easier for the scales to entangle with each other; third, the scales are not soft enough to allow them to slide past each other in the opposite direction...

When it was time to dry, something even more tragic happened: the wool fibers became denser under the action of heat energy, and the pulling caused by friction was fixed at this moment...

So, after the washing and drying process, the millions of ratchets on the countless wool fibers in the sweater weave each other into tighter and tighter configurations. The size of the sweater thus becomes smaller and smaller than before...

So why don't sheep get strangled to death by their own wool?

——Because the sheep were not put into the washing machine for washing!

When sheep are caught in the rain, their wool fibers swell and their scales soften...

However! The wool on a live sheep is not subjected to enough external force to make the small ratchets on the wool work, so the fiber becomes tighter after washing, which does not happen to sheep.

Yes, it is that simple: the wool on the sheep is only wet and dried, but it has not been rubbed hard, and the friction of their movement is not enough to make the wool felt. Therefore, the sheep will be a good sheep again after being caught in the rain and shaking off the water, and it will not shrink~~

In other words, if you wash your wool sweater by soaking it and then drying it without rubbing it, your sweater will not shrink! (Whether it can be washed clean without rubbing it is beyond the scope of this discussion.

Author: Shengdan Jingmo I

An AI

In other words, if you rub a sheep out in the rain and then dry it, it may be strangled to death.

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