Stretching hair

Hooke’s law can be a little ‘samey’ so why not try stretching horse hair? If pupils have stretched rubber and springs then they should be able to make a valid prediction with a reason.

Horse hair can be obtained from horses, music shops (for bows) and friendly equine owners.
Clamps can be made of two bits of perspex or wood held together with two bolts with wing nuts.

This is an experiment devised when I had no apparatus in a school where I’d taken over as HoD. I made the hair clamps out of off-cuts of perspex and bought some horse hair from a music shop. As we had no slotted masses I cut the tops off pop bottles, melted holes in the sides and put string through them to make little buckets. They were weighed and their mass written on them in permanent pen. Pupils then used measuring cylinders to add water as 1 ml = 1 g. This gave reasonable results and a need for some skill.

We stretched springs and then elastic bands and then the horse hair. The hair needs to be wet and it does creep when loaded slowly. I have had VIth formers doing coursework using more sensitive apparatus that they have constructed – mirrors on pulleys and laser beams magnifying the deflection.

All the experiments were done outside which made for more fun. We also tested shampoo’s claims that they strengthened hair; one company replied to a letter sent by another teacher explaining that the tests they did were different and hence their failure to find the strength increase.

Gary Williams

Themes: Forces and motion, materials

Equipment and supplies:

Horse hair can be obtained from horses, music shops (for bows) and friendly equine owners.
Clamps can be made of two bits of perspex or wood held together with two bolts with wing nuts.

does horse hair grow as long as the lenth of a violin bow?

Yes, pretty easily I think. Horse tails are quite long if you let them grow. Not sure about the double bass and cello bows though.

haha, sorry i was thinking about from the maine or the body, doh

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