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20 Minute Labs: Howling Ghosts

20 Minute Labs ghosts logo | Yellow Scope


trick or treat | Yellow ScopeHalloween is just around the corner - do you have your costume ready yet? Is your house decorated?

How about adding some spooky sound effects using science?! 

In this month's 20 Minute Lab, we'll experiment with  the concepts of motion and vibration to make some ghost balloons that howl in the night!

Greet your trick-or-treaters with a ghostly scream, or just try it our for fun at home! The more the merrier, so gather your siblings and friends together to make a whole fright of howling ghosts!

Our instructions call for white or clear balloons to make howling ghosts, but feel free to be creative. Maybe you'd prefer to make howling pumpkins with orange balloons, or screaming monsters with green or purple balloons...? There's no limit with your imagination!


  • ghost supplies | Yellow Scopepermanent black marker, like a Sharpie
  • 2 white balloons 
  • 1 penny (a marble works too)
  • 1 hex nut (Check your tool box, or you can buy one at the hardware store for a couple of cents!)
  • For bonus fun: Use a 36" balloon and a pump to blow it up.


    1. Use the black marker to draw ghost faces on both balloons. (You can do this before or after blowing up the balloons - before will give you a stretchy look.)
    2. hex nut in balloon | Yellow ScopePut the penny inside of one balloon.
    3. Put the hex nut inside the other balloon.
    4. Blow up both balloons and tie them off (or just hold them closed if you don't want to commit yet!).
    5. With a good grip on the balloon with a penny, make a quick circling motion so the penny moves around in a circle inside the balloon. What does it sound like?
    6. Now do the same to the balloon with the hex nut. What does it sound like?

    Take the experiment further by making different sized balloons, using multiple hex nuts, or even using a giant 36" balloon! What sound does that make?


    tetherball | Yellow ScopeWhy does the hex nut make the howling sound, while penny is quiet? Well, there's a couple things going on here.

    First off is the concept of force. A force causes a push or a pull. Did you notice that the penny spun and spun for a long time?

    That's because a centripetal force was acting on it. A centripetal force keeps objects moving in a circular path. This is the same force that keeps a roller coaster on the track through an upside down loop and also keeps a tether ball circling around the post!

    Because of the shape of the balloon, the penny goes in a circle. If you were to make the balloon disappear, the penny would fly off in one direction. Just like if you cut the cord of a spinning yo-yo, the toy would fly off in a straight line!

    Because of the penny's smooth, rounded sides, it travels across the material of the balloon without much resistance, or friction. The only reason it eventually winds down to a stop is because a different force - gravity - slowly pulls it down and out of its spin.

    hex nut | Yellow ScopeThe hex nut also moves in a circular path due to centripetal force. However, the nut has six flat sides. These sides bounce along the balloon's surface, creating a little bit of friction, but also lots of vibrations! These vibrations create sound waves, which are the source of that howling sound!

    What happens if the hex nut speeds up in its circling? Try it! You may notice that it gets much louder and higher pitched. What else could you try putting into the balloon? What results do you get?


    Let us know how your experiments turned out! Share your photos and results with us on Facebook, Twitter, Instagram, or send us an email to We love getting your messages!

    For more exciting experiments, check out our Yellow Scope science kits on the Shop tab of our website!

    Chelsea Schuyler
    Chelsea Schuyler