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. 

3 comments:

  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?

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    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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