BBC Science 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’S HAPPENING

Blowing into the harmonica makes the wide

rubber band vibrate, causing the air particles

around it to vibrate at the same frequency (you

can also feel the vibrations with your fingertips).

These vibrations pass from air molecule to air

molecule, producing a wave that travels away

from the harmonica. When this wave reaches your

ears, you detect it as sound.

The harmonica’s paper dividers separate the

rubber band into three different lengths. Blowing

through the ‘holes’ between the dividers produces

different notes because the different lengths of

rubber vibrate at different frequencies. The

frequency at which a rubber band vibrates is

proportional to how tightly it is stretched, and

inversely proportional to how long it is and how

heavy it is. This means that shorter lengths of

rubber vibrate at a higher frequency, producing a

higher pitched note. Blowing harder doesn’t

change the pitch of the notes, but should make

them louder.AS

WHAT TO DO

1.Cutout four paper rectangles, each roughly 4cm x 1cm.

2.Fold each piece of paper in half down its length three times to give four

folded pieces of paper, each roughly 0.5cm x 1cm.

3.Stretchthe wide rubber band around the length of one of the lolly sticks.

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

of the stick.

5.Putthe second stick on top so that the piece of paper is sandwiched

between the sticks.

6.Cutoff any paper sticking out from between the sticks.

7.Wrapa thin elastic band around the paper and sticks so that the paper is

held firmly in place.

8.Place a second piece of paper between the sticks, about 1cm along from

the first piece of paper. Again, cut off any paper sticking out, and secure the

paper in place with an elastic band.

9.Repeatwith a third piece of paper placed about 2cm further along.

10.Repeat with a final piece of paper placed right at the other end of the sticks.

11.Holdthe harmonica so that the rubber band is around the bottom stick and

blow through the gaps between the paper dividers. You should get three

different notes!

DIY

SCIENCE

RUBBER BAND HARMONICA

We’d love to see videos of your harmonicas in action. Send them to us on Facebook or Twitter(@sciencefocus)and we’ll share our favourites!