Saturday, November 16, 2013

Falling Balloon and Two Types of Air Resistance

A piece of advice for all of you science teachers out there...try out a lab at home or in your classroom before presenting to the class. Here I am working on the falling balloon lab. My advice in this lab I created was to include a coin in the lip of the balloon and drop it. However, soon, I found the coin was too heavy and decided to change to paper clips. One paper clip weighs about 1 gram.

This lab is about air resistance, including laminar and turbulent air friction. I have noticed that many labs only consider air resistance as an experimental error. However, it is not hard to create a lab focusing on air resistance using household materials, which will work for either an Algebra or Calculus-based Physics Class.  I am still editing the lab, but I will share it soon!

 I like to try out each lab with students a few times before sharing my labs with other teachers, and so far the students have enjoyed the lab and learned a lot, using only a few simple materials, including:

·         Several balloons
·         Meter stick
·         Stopwatch
·         Several coins or paper clips
·         Gram scale

Trying to capture another falling balloon drop...
sorry, I did not have my slow motion camera with me!

I hope this entry will inspire you to think about household materials that you could use in a simple physics lab in your classroom. Applying your creativity to creating new labs or demos can keep your teaching fresh and exciting. 


  1. Great point about testing things ahead of time. I do a Bernoulli demo with a leaf blower and a beach ball, but I've found that low ceilings can really affect the outcome. So now I always test it in whatever room I'm in.

    Do you have the students do the balloon without weights to try to struggle with the rotation that happens? I would imagine that even a very small weight would take care of that. Are you looking for terminal velocity, or just a smaller g, or something else?

    1. We look for terminal velocity, which changes with mass. However, is the predicting formula bV=mg or BV^2=mg. Solving for both b and B we can see which of the two remains the more constant during the lab. I drop the balloon from 2m and only time it for the bottom 1.5m. This measures the terminal velocity. The first data point is not very usable unless you have a highly symmetric balloon. Try it out, and find out if turbulent B or laminar b dominates.

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