Category: Physics (Page 3 of 7)

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.


  • 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.


  • 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.

Additional resources:

A classic activity is to inflate a balloon using vinegar and baking soda.

Steve Spangler has some ideas using balloons as well. Can you keep a balloon from catching fire?

He also has a balloon in a bottle.

The Book of Totally Irresponsible Science: 64 Daring Experiments for Young Scientists by Sean Connolly contains versions of these experiments.

Weekend Science Fun: Projects with Tin Cans

You won’t believe how many science projects you “can” do with a couple of tin cans.

With a tin can, you may investigate sound vibrations, friction, kinetic energy, potential energy and many more aspects of physics.

Before we start the physics, however, let’s do a bit of chemistry.  Is what we call a “tin can” really made of tin? How would you check?

It seems that the can our beans come in should be called a steel can because it is made mostly of steel, although it may have a light coating of tin to prevent rusting. Technically, if a can were made only of tin a magnet should not stick to it. Magnets are attracted to cans that contain iron, usually in the form of steel. Is a magnet attracted to your can of beans? What about an aluminum soda can? Pick up a magnet and find out.

What got us started with tin cans this week was an article in a book that promised you could get a tin can to roll uphill. When it did not work as the book suggested it should, we decided to investigate further.

Activity 1. Uphill Rolling Can


  • Clean, empty tin can* or similarly-shaped plastic container
  • modeling clay
  • cookie sheet or similar flat surface and a couple of books to make an adjustable ramp
  • rubber bands (optional) to give the can more grip

* Remove the lid of the can with adult supervision, and make sure there are no sharp edges.

Roll the can across the floor or on a table to see how it behaves. Build a ramp with a slight incline with the books. Try to roll the empty can up the ramp. What happens?

Now roll out a lump of the clay into a worm or snake shape. Attach the clay to one side of the can on the inside (see photograph). Roll the can across the floor or table. Does it behave differently than it did without the clay?

Try the ramp. Start the can with the clay up versus the clay down, until you can get the can to roll uphill. If it doesn’t work for you, adjust the steepness of the ramp. You can also put rubber bands around the outside of the can to increase grip. Make sure they are even so they don’t over balance the can.

Activity 2. Tin Can Car

You can take the idea of a self-propelled tin can a step further by creating a rubber band-driven version.

The idea is to put two holes in each end of the can (or can lids) that line up with each other, slip a rubber band (or similar elastic material) through the top holes and then add a weight in the center, in the middle of the can. Slip rubber bands through the bottom holes. Tie the ends. Roll the can and it should roll back on its own from the weight in the center.

PBS Kids has a good description of how to make a can car.

Description of a similar device from the November 1910 issue of Popular Mechanics. Be aware that ideas of safety were different back then. For example if you try this one, you should use a zinc sinker (available at fishing supply stores) rather than lead.

Activity 3. Tin Can Telephone

A classic activity is to make a telephone using two tin cans and a piece of string.


  • two clean, empty cans with the tops removed (or plastic cups work, too)
  • nail
  • hammer
  • goggles (for eye protection while hammering nail into can)*
  • string at least a few feet long

*Unlike in the video below, children should perhaps wear eye protection while creating the hole in the bottom of the can.

Hammer the nail into the center of the bottom of each can to create a hole. Remove the nail. Feed the string through the holes and tie a knot so that the knot prevents the string from coming out through the bottom. Both cans should now be connected by the string. Hold the two cans far enough apart so the string is tight. Take turns talking into the can and then listening to the other person talk.

You can even decorate your can like they did in this short video.

Activity 4. Musical instruments

1. Drum


  • clean, empty can or cans of various sizes with the tops removed
  • large balloons, at least one per can
  • scissors
  • chopsticks (optional)

Cut the stem off of a balloon and roll it over the top of a can. This is not as easy as it sounds, but if you can get a tight fit you will have a wonderful drum. Use hands or chopsticks to drum on the balloon top. Compare sounds of different-sized cans.

2. Tin can guitar


Activity 5. Sand Resistance (Advanced)


  • two cans
  • play sand
  • bin large enough to accommodate the two cans standing up plus sand

Fill a large bin with play sand. Press one can into the sand with the open end down. Press the other into the sand closed end down. Which has the most resistance? Sounds simple, but there are some complex physics involved.

To see the expected results, watch this video

For an explanation of the open can versus closed can in bucket of sand, see Science Now (website does contain ads).

A Few Other ideas:

Information about a stirling tin can engine in the Doable Renewables book review

4M Tin Can Robot

(Affiliate links)

4M Soda Can Robug

(Affiliate links)

When you are done with your can, remember:

“…one plant in a tin-can may be a more helpful and inspiring garden to some than a whole acre of lawn and flowers to another.” ~ Liberty Hyde Bailey

Hope you have fun with your tin cans.

Let us know how the activities turn out and if you have any other ideas for science with tin cans.


Bubble Gum Science

Our science fun this week was inspired by the nonfiction picture book Pop!: The Invention of Bubble Gum by Meghan McCarthy. Kids will enjoy the lively story of how accountant Walter Diemer started mixing this and that ingredient (at the factory where he worked), until he had invented a gum that could be used to blow bubbles. What a sweet tale!

This book just cries out for some hands-on activities.

Activity 1. Which type/brand of gum blows the best bubbles?


  • Several brands of bubble gum and regular gum
  • Ruler (decide on inches or cm)
  • Pair of tongs or cardboard bubble caliper (see below)
  • Volunteer(s) to chew the gum and blow bubbles
  • Paper and pencil to record the results

The most difficult part of this project is finding a standard way to measure bubbles that are often a moving target. Check this website for a photo of a “bubble caliper” used for measuring record bubbles. Think about how you might build something similar or find a pair of kitchen tongs that might open wide enough to accommodate the largest bubbles. Try to find the widest point of the bubble. Practice on a few bubbles to make sure your system works and is relatively consistent.

Predict which brand will produce the biggest bubble. Now give the volunteer(s) each one stick of each type/brand of gum. Allow them to chew the gum for a few minutes and then blow bubbles. When they are confident that they are blowing the best bubbles they can with that type of gum, have them blow a few more and measure them. Decide how many bubbles of each type of gum you are going to measure in advance, so you record the same number for each test.

When you are done, add up the size of the bubbles for each type, and then divide by the number of bubbles you measured for that type. This will give you an average. You might want to graph your results with a bar graph to easily see the differences between the brands/types.


Activity 2. What happens to the gum when you chew it? Does it gain weight from the moisture in your mouth, lose weight, or stay the same?


  • accurate kitchen scales
  • gum
  • wax paper to protect the scale (or the wrapper)
  • watch or timer

First, predict what you think  will happen. Take the wrapper off the gum. Place a piece of wax paper on the scale, and tare or zero the scale. If your scale does not tare, the record how much the wax paper weighs. Next place the dry gum on the scale. Record the weight (subtract the weight of the waxed paper if you did not zero it). Leave the wax paper in place.

Now chew the gum for one minute and weigh again. Record the weight. Weigh again at five minute and then at ten minutes of chewing. What is happening? Did the results follow your prediction? Try to figure out why or why not. Test more sticks and different kinds of gum, and have your friends and relatives try it, too. See if you get the same results.

Activity 3. Make your own bubble gum.

This video shows how bubble gum is made in a factory.

You can find kits and online recipes to make your own bubble gum (for example at Steve Spangler).

Try some other formulas, too. Be sure to write down what ingredients and the methods you use. Maybe with some time and the right ingredients, you could be the next Walter Diemer and discover something thrilling and new.

Links to other activities:

How long does sweet flavor last? How much sugar is there in bubble gum? See an experiment at Teach Engineering.

Why is it sticky? Learn more about the sticky properties of gum at Science in School.

Do you chew bubble gum? Let me know if you try some experiments with it. I’d love to hear what you find out.

Pop!: The Invention of Bubble Gum

A few other books and kits relating to bubble gum science:

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