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When my hair gets long I start doing a little flick of my head occasionally to get my hair out of my eyes.

This grows into a habit though, and for the first few days after cutting my hair I end up doing to same action. Interestingly enough when I have short hair I feel physical pain.

How come the same action hurts when I have short hair, but feels completely natural when my hair is long?

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closed as off-topic by David Z Mar 8 '14 at 9:15

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This is a wild guess.

You say the pain is in the temples, which is the kind of sensation you get if you whip your head around too fast. This therefore has nothing directly to do with the hair.

When you have long hair it "swings" around more, and you unconsciously synchronize the head flipping to this swinging. It makes sense to optimize this sortof "resonant" swinging, because that is exactly what you want to get the hair out of your eyes for the least head motion and jerkiness.

When you have short hair, there is nothing to synchronize to, and you flip your head more violently. This results in the bit of brain lodged in your head to bang around more and cause discomfort.

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So you're suggesting that I probably simply flick my head faster because I have no metric for gauging my speed? – Cruncher Mar 7 '14 at 20:52
@Cruncher: Yes. – Olin Lathrop Mar 7 '14 at 21:26
Interesting. It's plausible. Is it also possible that I'm applying the same amount of force with less mass and getting a higher accelleration? – Cruncher Mar 7 '14 at 21:27
@Cruncher: I can't imagine that the tiny extra mass of hair makes any difference to the accelleration. Think about it. What is the mass of your head? What is the mass of hair you get when cutting off the long hair? – Olin Lathrop Mar 7 '14 at 21:29
This is what I think happens too. There's no significant difference in the mass of your head, but you subconsciously swing your head at the right speed to swish your hair. With short hair, since you don't get the feedback you're used to, you move your head faster to find the effect, and end up going too fast. – krs013 Apr 4 '14 at 8:18

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