What you need:
- A large disposable plastic cup
- String (at least 20 cm long)
- Water or violin rosin (a sticky substance used to coat violin
bows)
How to:
Get an adult to help you with this step. Make a hole in
the bottom of the cup, just large enough to thread the string
through. You could thread the string through a large needle and use
the needle to make a hole in the base of the cup.
Tie a double knot at the end of the string inside the cup, to
ensure that it stays in place.
Cover the string that is outside the cup with violin rosin, if
available. If not, then just wet the string with a little
water.
Hold the cup with one hand. With the other, pinch the string
between your thumb and forefinger. Slide your fingers down the
string, while maintaining a firm grip on the string. You should
hear a "screaming" sound.
How does it work?
As you move your fingers down the string, it vibrates. This
vibration travels up the string into the cup, where is amplified -
think of how a loudspeaker works. We hear these amplified
vibrations as "sound". Violin rosin or water increases the
stickiness of the string, increasing the number of vibrations set
up in the string.
Try repeating the experiment with different sized cups, and
strings of different length, to see what effect this has on the
"screams". Will a paper cup behave differently to a plastic
cup?
By Zara Mahmoud