## Weekend Science Fun: Balloon Physics

Last week we met with some fellow science enthusiasts and had a quite literal blast. The idea was to do as much science as possible with a simple resource:  balloons!

Note:  Some balloons are likely to pop loudly during these activities. Keep balloon bits away from small children and pets.

Gather:

• large balloons (12" party size)
• bamboo skewers
• metal hexnuts (as smooth as possible - see photograph)
• dish detergent and/or vegetable oil
• paper plate

Activity 1. Can you insert a bamboo skewer through an inflated balloon without popping it?

The answer is yes, but it requires a bit of knowledge. First, it helps to lubricate the skewer with a bit of dish detergent or vegetable oil. Place the soap or oil in a paper plate and roll the skewer in it.

Inflate the balloon and tie it. The idea is to insert the skewer in the areas of least tension, which is where the latex is darkest, typically where the balloon is tied and directly opposite at the tip of the balloon. Gently work the balloon into the area near the knot and pass it through the center of the balloon. Using a brisk motion, slide it back out through the balloon at the top.

Now you have an inflated balloon on a skewer!

If you used soap, experiment and try oil. What happens if you try to put the skewer in where the latex is thin (nearly clear)?

Activity 2. Making a balloon sing.

Have you ever let air out of an inflated balloon and had it screech?

You can also make a balloon "sing" by inserting a metal hexnut into the un-inflated balloon. Once the hexnut is inside, inflate the balloon as usual and tie it. Now rhythmically shake the balloon. The idea is the get the hextnut to whirl around, creating a vibration. Once you get the hang of it, experiment. Does how fast you whirl it change the pitch? How about the size of the balloon? What happens when you add two or more hexnuts? Make a prediction and then test it.

Activity 3. Decorate a balloon with cups.

For this one you'll need:

• rigid plastic cups- 6 oz size
• water supply
• balloons

Lightly wet from four to six plastic cups. Begin to inflate the balloon until it is about the size of two fists. Press one cup on the balloon surface and continue to inflate slowly. The cup should be held in place by air pressure. Press another cup. See how many cups your balloon will hold before it is fully inflated. If you are having difficulty, try pressing the sides off the cup in a little bit prior to applying. This one takes a little practice, but it does work.

Activity 4. Fast flying balloon.

Have you ever let go of a balloon that is blown up fully, but before you tie it. Did it fly around the room? You can harness that thrust to study it.

This is easier with at least two people.

Gather

• long, narrow balloons (work best for this)
• kite string at least 15 feet long
• tape
• straw (preferably wide and not the bendy kind)

Tie one end of the kite string to a doorknob, chair or stair rail, below the height you can reach. Feed the other end of the string through the straw and back up to hold the string tightly. Test if the straw will travel freely down the string to the other end. Bring the straw back and either have someone hold the end or tie it to another surface that is at the same height or higher than the first. Inflate the balloon, but don't tie it. Tape the straw to the inflated balloon so that the open end of the balloon faces back. Release and let the balloon shoot along the string.

See if you can modify your set up to make the balloon travel faster.