BBC Focus - 03.2020

Q&A

GET T Y IMAGES X2 ILLUSTRATION: DAN BRIGHT

WHATYOU’LL

NEED

■Paper

■Twoicelolly

sticks

■Onewide

rubberband

■Fourthinrubber

bands

■Scissors

WHAT’SHAPPENING

Blowingintotheharmonicamakesthewide

rubberbandvibrate,causingtheairparticles

aroundit tovibrateatthesamefrequency(you

canalsofeelthevibrationswithyourfingertips).

Thesevibrationspassfromairmoleculetoair

molecule,producinga wavethattravelsaway

fromtheharmonica.Whenthiswavereachesyour

ears,youdetectit assound.

Theharmonica’spaperdividersseparatethe

rubberbandintothreedifferentlengths.Blowing

throughthe‘holes’betweenthedividersproduces

differentnotesbecausethedifferentlengthsof

rubbervibrateatdifferentfrequencies.The

frequencyatwhicha rubberbandvibratesis

proportionaltohowtightlyit is stretched,and

inverselyproportionaltohowlongit is andhow

heavyit is.Thismeansthatshorterlengthsof

rubbervibrateata higherfrequency,producinga

higherpitchednote.Blowingharderdoesn’t

changethepitchofthe notes, but should make

them louder.AS

WHATTODO

1.Cutoutfourpaperrectangles,eachroughly4cmx 1cm.

2.Foldeachpieceofpaperinhalfdownitslengththree times to give four

foldedpiecesofpaper,eachroughly0.5cmx 1cm.

3.Stretchthewiderubberbandaroundthelengthofoneofthelollysticks.

4.Placeonefolded piece of paper on top of the rubber band at one end

ofthestick.

5.Putthesecondstickon top so that the piece of paper is sandwiched

betweenthesticks.

6.Cutoffanypaperstickingoutfrombetweenthesticks.

7.Wrapa thinelasticband around the paper and sticks so that the paper is

heldfirmlyinplace.

8.Placea secondpieceofpaperbetweenthesticks,about1cmalongfrom

thefirstpieceofpaper.Again,cutoffany paper sticking out, and secure the

paperinplacewithanelasticband.

9.Repeatwitha thirdpieceofpaperplacedabout2cmfurtheralong.

10.Repeatwitha finalpieceofpaperplacedrightattheotherendofthesticks.

11.Holdtheharmonicasothattherubberbandis aroundthebottomstickand

blowthroughthegaps between the paper dividers. You should get three

different notes!

DIY

SCIENCE

RUBBER BAND HARMONICA

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