Explaining Bernoulli’s Effect to a 5-year-old

If I stated Bernoulli’s principle to my 5-year-old, I’d probably get crickets or millions of questions as he would try to understand this word soup (for a young kid, anyway.) Ok, let’s try it:

If no energy is added to the system, an increase in velocity is accompanied by a decrease in density and/or pressure. The law is directly related to the principle of conservation of energy.

Hmm, he picked option c.) mumble “Ooooookaaaaay” and walk away.

What if I tried a different approach? Here goes nothing:

Explaining Bernoulli’s Effect to a 5-year-old

Can you throw a ball?

Can you throw water? (Pro tip: make sure you ask this question outside.)

How about gas? Can you throw air? After all, air doesn’t hold it’s shape the same way solids or liquids do: you can’t grab a handful or pour a glassful of air. Go ahead, try it!

This experiment will demonstrate that air, like other matter, responds to force. We will apply force to the air molecules and throw them! We will send them flying in a single direction using Bernoulli’s Effect. We are going to throw air!

Materials needed for this experiment:

Let’s start small:

  • Plastic or paper cup
  • Large balloon or a heavy duty trash bag
  • Rubber bands
  • Scissors
  • Adult supervision and help
  1. Cut a hole in the bottom of the cup. The plastic cup we bought kept breaking, so we ended up using heated knife to create the opening. (Please, please, please use caution and responsible adult’s help!!!) To avoid sharp heated objects, use paper cups.20180127_214254
  2. Create a membrane that will go over the top of the cup by cutting off the neck of the balloon or by cutting a circle out of heavy duty trash bag/shower curtain. Stretch it over the lip of the cup and secure with the rubber band.20180127_214301
  3. Point your air cannon at the lightweight object, gently pull back the membrane, then release it. You can also fire your air cannon by tapping the membrane.
  4. Play around with the size and shape of the container, shape, size or the position of the opening. Which changes improve or diminish your air cannon’s performance?
  5. Optional: fill the plastic cup with water vapor (made with dry ice or fog machine) or smoke (smoke bomb.) Repeat steps 3 and 4.

Fun experiment, isn’t it? Let’s multiply the fun factor by making it BIGGER!!!!

*****Since this project is much more labor intensive and attention demanding than the small one, we made this version of air vortex cannon during kids’ nap time.*****

For the giant version of this experiment you will need:

  • 32 gallon plastic trash can
  • heavy duty trash bag or a plastic shower curtain.
  • bungee cord
  • box cutter
  • Adult supervision and help
  1. Using the box cutter, cut a 6″ hole in the bottom of the trash can (most trash cans have a line that will guide you.)20180127_215115
  2. Cut a piece of heavy duty trash bag and attach it with bungee cords over the top of the trash can. Option 2: use duck tape to secure the membrane to the opening. We added a bungee type cord handle for bigger…”kick.”20180127_215126
  3. Point your air cannon at the target (solo cup tower or a balloon) and gently tap the membrane.
  4. Oooooh and aaaaah
  5. Play around with the size and shape of the container, shape, size or the position of the opening. Which changes improve or diminish your air cannon’s performance?
  6. Optional: if you have access to fog machine or another smoke source…USE IT!!!! Fill the inside of the air vortex cannon with smoke from available source and repeat step 3. The rolling rings of smoke will demonstrate Bernoulli’s effect.

The science behind the experiment:

Bernoulli’s principle states that the faster air is moving, the lower its pressure. The air inside the vortex ring moves faster than the air outside the vortex. The pressure inside the vortex is higher than the pressure outside. When the membrane is pushed forward, it rushes the air molecules toward the air cannon opening. This action causes a chain reaction of air molecules crashing into each other on their way out. The outer edge of this moving air is rolling backwards on itself and… whoosh! A stream of air rushes straight out of air vortex cannon.

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