Never enough screaming ghosts

Ooooh Halloween is just around the corner now! Time is running out for our spooky science series, but this week I thought we would do one more scary science experiment. In the spirit of Halloween, this has been one of my favourite activities to do with groups lately. My theory is that one can never have too many ghosts screaming throughout the house this time of year.

*Remember to ask an adult before doing this experiment.

Materials

- disposable white plastic cup - thin string - button - small piece of sponge - water - nail or scissors

Procedure

1. Using the nail (or scissors), carefully push a hole in the middle of the bottom of the cup. About one centimetre away from the first hole, make another hole.

2. This is a bit tricky, starting from the inside of the cup, thread the string through the first hole and then around the bottom of the cup on the outside, and back in. Tie the string in a knot so it is secure. If you hold the cup upside down, the string will be dangling out from the middle of the inside of the cup.

3. Using the scissors, poke a hole in the middle of the piece of sponge.

4. Pull the string through this hole in the sponge.

5. Tie a button onto the end of this piece of string to keep it from pulling through the sponge.

6. Wet the sponge with water. Squeeze it out so it is just moist, not dripping wet.

7. Pull the sponge to the top of the string.

8. Wrap the wet sponge around the top of the string.

9. Gently squeeze the sponge against the string as you move the sponge down the string using jerky movements. You will hear an eeeerie ghost in the house!

What is going on?

Although the sponge is wet, there is still enough friction caused between the sponge and the string allowing the string to vibrate. As you pull the sponge down the string, you will feel it skip and bounce down. This irregular touching on the string produces tiny taps that force the string’s molecules to move back and forth. The vibrating string strikes the molecules in the cup, and the cup’s molecules strike the air molecules causing them to move back and forth in rhythm with the cup and string. The sound is made louder because the inside of the cup acts like a megaphone that concentrates the sound waves and sends them out in one direction. We are celebrating our 25th annual Family Science Olympics at Medicine Hat College today. There is fun for scientists of all ages! Drop in any time between 10 a.m. and 3 p.m. I would love to see you!