Today you are going to do two different activities with balloons. Remember when we bent a stream of water with static electricity? If not, check it out here: http://discoveryexpress.weebly.com/homeblog/bend-a-stream-of-water-with-static-electricity
You are going to use that same concept to magically move an aluminum can with a balloon... WITHOUT ever touching the two items together! How will you do that?
Sometimes, electrons can transfer from one object to another. When an object gains electrons, its charge becomes negative. When an object loses electrons, its charge becomes positive. As you can see below, an electron left a sodium atom and transferred to a chlorine atom. What happened to the charges of the atoms? Why?
YOU WILL NEED
- A head of hair
- Empty aluminum can (a pop can would work great)
Here’s what to do!
- Blow up the balloon and tie the mouth of the balloon in a knot.
- Place the empty aluminum can on a flat surface.
- Rub the balloon back and forth on your hair really quickly for ten seconds! By the end, you’ll probably look like this:
Remember, this is not magic! You used the power of static electricity to move the can. When you rubbed the balloon on your hair, it gathered electrons. Remember, electrons have a negative charge, and opposite charges attract. Negative charges can also attract items with a neutral charge. Because the balloon now has a negative charge, when you bring it near the neutrally charged aluminum can, the balloon attracts the can and causes it to roll towards the balloon.
Just how strong is the static electricity created by your hair and the balloon? Try adding water to the can to make it heavier. Can you still get it to roll towards the balloon? How much water can you add before it won’t roll anymore?
If you use a bigger balloon, is the static electricity stronger? What if you rub the balloon on your hair longer? Test it out! Make sure to record your findings in your observation notebook!
In the next activity, you are going to explore polymers, just as you did a few weeks ago when you compared two different kinds of slime. If you missed it, check it out here: http://discoveryexpress.weebly.com/homeblog/two-times-the-slime-fun-with-polymers
Let’s back up... what exactly is a polymer, anyway? A polymer is a large molecule, or macromolecule, that consists of many repeated subunits. Polymers are created by linking smaller monomers into a chain. Think of the monomers as beads, and the polymer as a necklace made by stringing the beads together. See image below:
YOU WILL NEED
- Two balloons
- Cellophane tape (like Scotch tape)
- Petroleum jelly (such as Vaseline)
- A sharp pin
- A wooden or metal skewer
Here’s what to do!
- You can reuse your balloon from the previous experiment.
- Place a piece of cellophane tape on the balloon. Predict: Can tape keep a balloon from popping? Why or why not?
- Pick up the pin and stick it into the balloon where the tape is. Did it pop?
- Now stick a second pin into the balloon where there is no tape. BOOM. It pops! Why would tape keep a balloon from popping?
Explanation: Balloons are made of rubber, which is a polymer. When polymers are attached together, it is called cross-linking. These links allow polymer molecules to stretch to certain point without breaking. When you place tape on the balloon, the tape reinforces those cross-links, so when you stick a pin into the taped area of the balloon, the balloon does not pop. When you stick a pin into the untaped area of the balloon, the cross-links are broken and the balloon pops.
- Now let’s take it a step further. Blow up a new balloon, but make sure it is not entirely inflated. It should be about the size of a cantaloupe.
- Grab a gob of petroleum jelly and rub it on the skewer. Make sure the entire skewer is coated.
- Pick up the balloon and carefully insert the skewer into the end of the balloon opposite the knot. If you are careful, you should be able to stick the skewer all the way through the other side of the balloon without popping it.
- Coat a second skewer with petroleum jelly. Try sticking it into the side of the balloon. What happened? It popped! Why would sticking the skewer into the side of the balloon be any different than sticking a skewer into the bottom of the balloon?
Explanation: The ends of the balloon have more rubber that isn’t as stretched out as the rest of the balloon. There isn’t as much force pulling on those areas. Because the ends have more polymer molecules clustered together, the skewer can pierce the ends of the balloon and simply push the polymer molecules aside without causing the balloon to pop. When you stick the skewer into the side of the balloon where the molecules are spread out and have more force pulling on them, the tension is too great and the balloon pops.