Whet your thirst for science and learn about vibrations with three activities using a cup or a glass.
SPITTING STYROFOAM
WHAT YOU NEED:
• Styrofoam cup
• towel
WHAT YOU DO:
Fill the cup with water and then push it gently across a smooth, dry surface (such as a table top). If you achieve the right speed, water should spit all over the place!
If it doesn’t work, try moving the cup at different speeds or over a different surface. Make sure you mop up any spilt water, as this experiment will only work on a dry surface.
WHAT’S GOING ON?
As you push the Styrofoam cup across the table it will alternately slip across the surface and then stick to it. This causes both the cup and the water inside it to start vibrating.
These vibrations cause waves on the surface of the water. If you move the cup at the right speed, the waves will start building upon each other, making the peaks higher and the troughs lower. Eventually some water will break free of the peaks and splatter out!
CLUCKING CUP
WHAT YOU NEED:
• plastic cup
• string (such as cooking string)
• nail
• hammer
• small square of dishcloth
WHAT YOU DO:
1. Ask an adult to help you use the hammer and nail to make a small hole in the bottom of the cup.
2. Turn the cup upside down and then dangle about 20cm of string through the hole (like a hammer in a bell).
3. Tie the string into a large knot so that it can’t fall through the cup.
4. Wet the dishcloth and then pinch it around the string just under the cup.
5. Grip it tightly and then pull the cloth slowly down the string.
I bet you didn’t realise a cup could cluck!
WHAT’S GOING ON?
When you pull down on the string, the dishcloth alternately slips and sticks to the string. This vibrates the string, which in turn vibrates the cup, which vibrates air in and around the cup. The vibrations in the air reach your ears, shaking your eardrums which send information to your brain where it is interpreted as a ‘cluck’ sound!
WINE-ING GLASSES
WHAT YOU NEED
• wine glass with a thin lip
WHAT YOU DO
Wet a couple of your fingers and gently run your fingertips around the lip of the wineglass several times. It should start to sing.
If it doesn’t work, experiment with how hard you press against the glass (not so hard that you cut yourself).
WHAT’S GOING ON?
You’ve probably worked out what’s going on by now! As you run your fingers around the lip of the glass, your fingers will alternately stick and then slide against the glass. The glass vibrates, the air vibrates, your eardrums vibrate, and you hear a beautiful singing sound!
Try filling the glass with varying amounts of water to change the sound.
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