Spring is in the air, so I wanted to revisit a crowd-pleasing program for my crew: balloon science! You’re never too old to have fun with balloons, and our Prosser Science Explorers discovered just how many interesting things we can learn with a little help from our piles of balloons! With a few simple demonstrations, our group was able to discuss:
- Air Pressure
- The Properties of Polymers
- Centripetal Force
- Newton’s 3rd Law of Motion (we ran out of time to do this as a group during the program, but I gave instructions and materials to the scientists to take home)
We started the night with a brief presentation and a discussion about the properties of polymers. In particular, how the rubber in balloons is made of long strands of molecules called polymers. And it is the elastic quality of the polymers that allows the balloon rubber to stretch.
Our conversation then turned to centripetal force and friction. The word “centripetal” is actually Latin for “center seeking.” And that truly describes this force. Without centripetal force, objects would not be able to travel in a circular path (they would only be able to travel in a straight path). One example is how a satellite orbits the earth. In this case, the centripetal force is supplied by earth’s gravity (think of it like an invisible thread that links the earth to the satellite and keeps the satellite moving around the earth in a circular orbit). Another example is the swings ride at an amusement park (see picture above), where the centripetal force is supplied by the chains that link the chairs to the central pole. To help with this subject matter, I shared one of my favorite youtube videos on the topic with our group. In the following video, Jeff Williams on the International Space Station (ISS), shows that, due to centripetal force, the bubbles in his iced tea package move to the center of the package and form a large, singular air bubble when the package is put into a circular path.
DEMONSTRATION – Air Pressure
I was inspired to do this demonstration after reading a blog post by Darcy Zalewski. With just a few simple supplies you can demonstrate low air pressue.
- Mason Jar (I used a very large jar, but any size will do just fine)
- lighter or matches
- paper or candles to burn inside the jar
I chose to use tea-light candles to burn inside my jar because they are easy to light and they hold a consistent flame (thus, I didn’t have to worry about a piece of paper burning out quicker than I could do my other steps). I had a balloon ready to go off to the side. I had attached the open end of the balloon to a kitchen faucet to fill it with a good amount of water (approximately a cup), and then I inflated the balloon until it was just larger than the mouth of the jar and tied it off.
Once the candles were lit, I sat the balloon on the open mouth of the mason jar. Initially, the balloon vibrates a bit as warm air is sneaking past the balloon and outside the jar. But then the polymers of the balloon start to stretch and the close off the mouth of the jar. The candles slowly use up whatever air remains in the jar and then go out because they have used up all available air. This creates a low air pressure environment in the jar similar to a vacuum, and the balloon is actually partially sucked into the mason jar.
ACTIVITY #1 (Polymers): The Balloon Skewer, or what I call, “Balloon on a Stick”
- Clear balloons are a must (I bought a package of 70+ on Amazon)
- Wooden skewers (the longer the better – again I found some at a party store, but I know some grocery stores have them as well)
- A small piece of sandpaper (to smooth out any rough surface on the skewers)
This is definitely an activity designed to impress a crowded room 🙂 My idea for this activity came from my favorite scientist Steve Spangler and a demonstration from his web site called The Balloon Skewer. Thanks to the properties of polymers, you can push a skewer in one side of the balloon and out the other side…without popping it! [The trick is making sure the entry/exit points are where the balloon’s rubber is LEAST stressed, or more opaque looking then the rest of the balloon – near the base where you tied off the balloon, and at the opposite end and top point of the balloon.] Each scientist was given a clear balloon and a skewer to try their hands at this demonstration. An important early step is to inflate the balloon as large as you dare, and then release 1/3-1/2 of the air before you tie off the balloon. This actually helps stretch out the polymers and gives you a better chance at success when you aim to slip the wooden skewer between the polymer chains and through the balloon itself. Though all of my balloons popped, all of the young scientists were able to have success after a few tries. Practice makes perfect!
ACTIVITY #2 (Centripetal Force & Friction): The Spinning Penny
- Clear balloons are a must
- One penny per person
With our next activity, we had a chance to see centripetal motion at its best. The Spinning Penny is a demonstration described on Steve Spangler’s web site. The demonstration itself is very simple. A single penny is placed inside a clear balloon before you inflate it. The balloon is then inflated and tied off with the penny still inside. After shaking the penny a bit, the balloon is then swirled to help start the penny on a circular path inside the balloon itself. Due to the limited amount of friction, the penny can stay on its circular path for close to 30 seconds before gravity begins to slow it’s path! Our scientists all managed to create this very cool demonstration of centripetal force and (lack of) friction. [Special Note: It is important that the balloon is pointing toward the floor when you inflate it – there is a danger of a choking hazard if you choose to tip the balloon above your head to inflate with the penny inside!]
ACTIVITY #3 (Centripetal Force & Friction): The Screaming Balloon
- Clear balloons are a must
- One zinc hex nut per person (any smaller size works fine, for example a 1/4 inch nut)
This demonstration is actually a fun variation to The Spinning Penny. For The Screaming Balloon, we replaced the penny with a zinc hex nut…and guess what? The nut also moves on a circular path within the balloon due to the centripetal force we supply, but there is more friction between the hex nut and the balloon thanks to the the shape of the nut, and thus we get a high-pitched whining sound! Very fun for us…maybe not so fun for friends and family 🙂
ACTIVITY #4 (Newton’s 3rd Law): Balloon Rockets
Sadly, we ran out of time for this particular activity. But I sent all of the scientists home with supplies and instructions for how they could do this at home. I’ll also describe the activity below…
- Any balloons will do (we made sure everyone used the same size balloon for fairness since we did some mini races)
- Straws (if you have the bendy kind, you can just cut off the bendy portion…I actually used milkshake straws because they have a larger opening)
- Tape (any kind will do – we used scotch tape)
What better way to see Newton’s 3rd Law of Motion in action than some friendly competition with balloon rockets! According to Sir Isaac Newton and his 3rd Law of Motion:
For every action, there is an equal and opposite reaction
To test this principle, I like to follow the guidelines of Science Bob to create balloon rockets. You need to create a path for the balloon to travel along. I usually use a pair of chairs spaced apart across a room. You will then attach a long piece of string to one chair, leaving one end free to slip your straw onto. You can then attach the second end of the string to the second chair. Your string should be tight/taut, and it should be level (not slanting up or down). Now you choose any balloon (it doesn’t have to be clear) and you inflate it as large as you want without tying it off. While pinching the open end of the balloon closed, the balloon is held under the straw and taped to it (with the mouth of the balloon pointing in the opposite direction that you want the balloon to travel in). When you’re ready to the see the balloon in action, you just unpinch the mouth of the balloon and let go! The result mimics the take-off of a rocket, with the air pushing back in one direction and propelling the balloon in the opposite direction.
You can create a true experiment by testing variations – blowing up the balloons to various sizes, trying different strings, etc.