Determine the Speed of Sound in Your Classroom

Here's my latest addition to the FLOSScience site. In this installment I introduce a procedure for determining the speed of sound in your classroom. As usuall, below is only the first part of the procedure. For the full procedure you'll need to this entry on the FLOSScience Probeware Site.

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will go through a process that will allow you to determine the speed sound travels out to four significant figures with less than a 3% error. This is a classic physics lab that in the past would have required lots of expensive equipment to ensure this degree of precision and accuracy. The only expensive equipment involved here is a computer with a microphone input. Which by itself can be expensive, but most classrooms these days have at least one in the room.

Step one -Stuff You Need

1. Computer with microphone input.
2. Microphone you can plug into the computer. I use some cheap headsets that I bought on ebay for $4.50 each. Really any microphone that you can plug into your computer will do (even USB microphones).
   
3. Long tube, 1.5 m to 2 m in length is best. You can use PVC pipe, but I typically use "carpet tube". That's the cardboard center of a roll of carpet. You can get this for free from any store that sells carpet. Just go look near their dumpster, or if you're feeling slightly ambitious you could ask a salesman.
   
4. An audio recording program. I recommend Audacity. Really any audio recording program that will show you a sonogram will work. Note: I've tried Garage Band on my MacBook, but I can't zoom in enough to see the required detail to make this work.

Site Update - Cheap and Easy Infrared Photography

On the FLOSScience site are some instructions for converting a web cam for cheap, easy infrared photography. Basically, all digital cameras are capable of detecting infrared radiation just outside of the visible spectrum. That is to say light with a longer wavelength than the red end of the spectrum. With some slight modification we can filter out the visible light and let through the infrared light. However, this will not allow you to do thermal imaging, which is done in the far infra red.

The video below shows what happens when you simply put a filter suitable for infrared photography in front of the web cam ($25 from Amazon). It works, but the results are much better if you put the filter inside the camera instead.

Build Your own Probeware

I teach high school physics and I use a lot of expensive probeware to collect data. The only reason I can do this is my school has been collecting the probes over a number of years, building our collection slowly over time. For those who aren't science teachers, probeware refers to a collection of interfaces used to connect a variety of sensors to a computer or graphing calculator. These interfaces can allow for real time data collection and graphing or can serve as data-loggers collecting data over time.

The two largest vendors of educational probeware are Vernier and Pasco:

• http://www.vernier.com/
• http://www.pasco.com/

Not every school has the ability/money to do probeware based labs, however. So, here is a description of how to create a really simple probe that will allow you to see the fluctuations in light caused by alternating current or see the signal from a TV remote control.

Total cost is less than $10, but you need a computer with an oscilloscope program installed.

Visual Analyser - Free oscilloscope program for Windows. http://www.sillanumsoft.com/

Audacity - Can be used as a recording oscilloscope. http://audacity.sourceforge.net/

Follow the instructions on the FLOSScience site or print out this illustrated guide in pdf form.

GIS - Geographic Information Systems

I taught Environmental Science a number of years ago and I came across all of this then. Some of this material may be a little outdated. I will be working on it this summer to help out a good friend of mine who will be teaching Environmental Science this year. GIS, or Geographic Information Systems, is basically taking data and plotting it on maps. By mapping the data it is often much easier to spot patterns or trends. In education GIS can be a perfect tool for inquiry based labs.

The simplest GIS activity I've ever done with my class was to pass out maps of South East Michigan that I'd gotten from the Secretary of State or the Department of Transportation (I can't remember which). Then in groups of trhee I had students use markers or crayons to trace all th rivers and streams. By highlighting this data students were able to quickly identify the different watersheds in our area. We live in the Rouge River Watershed which covers a large area and funnels down to one very polluted river. Once the watershed was "outlined" in this way it was easy for students to understand why it is still so polluted even given all the programs aimed at changing this.

GIS becomes even more powerful when we bring the power of computers to bear. Below are listed some free programs for analyzing data. The easiest is probably Google Earth, but I highly recommend giving ArcExplorer a try.

• NASA World Wind - Free and Open Source program from NASA. Visualize the Earth as a 3D globe that you can easily map a variety of data onto. Yes, I know this sounds a lot like Google Earth. It is not quite as easy to use as Google Earth, but it already includes much of the scientific data that you have to download separately and add into Google Earth. You should give it a look and see if it will give you a few more things than GE will. It also includes the Moon and Mars. Be sure to check out the World Wind Wiki for more info and add-ons. The World Wind Wiki offers a comparison with Google Earth. Or if you prefer, here's a 3rd party comparison.
  
• Google Earth Ideas - Google Earth is free from Google, although there are paid versions as well. The newest version allows for easy integration of SketchUp Buildings.
• Arc Voyager SE - Cool program that comes with ready made activities. ArcVoyager really begins to show the power of GIS. (This is still available, but it has been supplanted by Arc Explorer. Personally I haven't used ArcExplorer in class yet, which is why I still list ArcVoyager)
• Create Custom Maps from online data. (Earth Exploration Toolbook)
• Earth Science Lesson focusing on mapping earthquake data. (Earth Exploration Toolbook)
• Looking into the Earth using earthquake wave speed data. (Earth Exploration Toolbook)

I created this map as an example of some of the cool questions you can ask. It was created in ArcExplorer using data from the 2006 CIA World Fact Book. The highlighted countries have more than twice as many active cell phones as traditional telephones. This is really cool, it demonstrates how many developing countries are leap-frogging technologies and not even bothering to build the infrastructure necessary to support more out dated traditional phones.

Limitless, Free (or nearly free) Lights!!! - Clever Hacks

So, now you have your cheap generator. Now what can you do with it? You need some sort of "load" the easiest is some sort of light bulb. The classic way is to use a 5 v miniature screw in bulb. But, these can get a bit pricey, especially when students try their hardest to crank as fast as they can to see if they can burn them out (if you've done this lab you know exactly what I'm talking about).

So, what's a cheap, lazy physics teacher to do? Well, J.D. Birchmeier has allowed me to post his "Physics of Christmas Lights" writeup on the FLOSScience site. You can often find whole strings of these that people are too lazy to troubleshoot. Just ask your students to keep their eye out for lights headed towards the trash after Christmas. Even if you don't get them for free, if you buy them after Christmas when the stores are clearing them out you can get them for just pennies/bulb. Much cheaper than through traditional science supply outlets.

The other piece that makes hand crank generators cool in class are supercapacitors. Again, if you take the easy way and go to traditional science suppliers you will likely pay around $20. However, a quick Google search will find many different suppliers of similar capacitors for under $5/each. Occasionally I've even seen some for under $2/ea (but you gotta catch them on sale).

DIY Generator - Clever Hacks (Site Update)

The Back Story
A couple of years ago I got to sit in on a demonstration of a really cool inquiry based lab run by Mark Davids. In this lab each student group is given a

plastic shoe box containing: two light bulbs, a 1 Farad super capacitor, some alligator leads, and a Genecon Hand Crank Generator. They are then told to "play" and record their observations. They quickly find out that cranking the generator is much harder with a load (moving electrons = work) and the capacitor stores electricity in some way. After playing for a little there is a class discussion to share ideas. These ideas can lead to quick experiments to confirm or refute these ideas. This was one of those "AH HA" moments for me. It was a very influential experience and has changed the way I approach many of my labs.

I haven't been able to do this lab with my class. I only have one Genecon and I don't have a large enough budget to justify buying 10-15 of these at $50 each.

The Solution
While cleaning this summer I stumbled upon a flashlight with a hand crank that I'd bought my son for our last camping trip and out of the blue I had a

thought. Could this be used instead of a Genecon? How much do they cost? ($10 at Amazon) As it turns out I had a couple at school that a student had brought in for a project relating to generators, but in the end we didn't use them (he had gotten them for free).

I haven't used these in a classroom situation yet, so I don't know if they will be as robust as Genecons. But at $6/ea they are cheaper than the $7 Genecon replacement gears. The output seems similar. I haven't done extensive testing yet, but load voltage is about the same for the same load.

This hack is pretty straight forward, but I do have detailed instructions on the FLOSScience site if you need them.

HotWheels Radar Gun - Cheap Tech Toy (Site Update)

I bought a Hot Wheels Radar Gun to see if it was at all useful in physics or physical science. The radar gun is hand-held. While it was designed for smaller hands than mine (go figure, 38 year old physics teachers aren't the target audience) it is still easy enough to hold and use. You have two unit settings kph and mph and you have the choice of getting straight speed or hotwheels car scale speed (1:64). I've of course been working in scale speed so I can be more precise (hopefully). When you pull the trigger you get a live readout of speed. When you let go it reports the maximum speed measured. I haven't developed any labs for this yet, but here's what I've been able to discover.

Experiment #1: Determining g using a falling object (a book)

• I held the radar gun above the book pointed down
• The book is held 2 m off the ground and dropped
• Velocity is taken in kph with the scale speed setting (1:64)
• Result - using the equation a=(v^2)/(2d) I get a value of 5.16 m/s/s. Only about a 47% error. (were shooting for 9.8 m/s/s)

Observations from Expt. 1

• If the book drifts out of the radar beam I don't get really big numbers. I've done this same experiment using Vernier motion sensors and if your target moves out of the "beam" the floor is shot given the impression that the object "teleported" instantaneously to the floor resulting in a really big velocity.
• The results are the same if the object is held really close to the gun as they are if you start further away. The Vernier motion sensor can't get a reading within 0.5 m or so.
• It was really hard to get consistent results. Two out of three results would be the same, but the third would be wildly different.
  

Conclusions from Expt. 1

• The "reaction time" of the gun may be slow. This would explain the lack of teleportation velocity and may explain why I never got a true value for the maximum velocity of my falling object. It may very well be that the gun doesn't work well with accelerating objects and will give me more consistent results with constant velocity objects.

Experiment #2: Constant velocity. While riding my son's scooter I have my GPS unit. The settings are mph (same as the GPS) and scale speed for greater precision. When in real speed, speeds are reported only to the nearest mile per hour.

• Read GPS unit wile attempting to not fall off and not run my son down (while going between 8 and 9 mph).
• My son shoots me with the radar gun staying in my path just long enough to get a good reading before diving to safety.
• Compare the results.

Observations from Expt. 2

• The results are much more consistent than in Experiment #1.
• The numbers from the GPS unit and radar gun are fairly similar. It's tough to get a good reading from the GPS unit while not running my son down.
  

Conclusions from Expt. 1 and 2

• My initial conclusions seem to be confirmed. A constant velocity seems to give a better answer. There was a 13% error between the radar gun and the GPS velocities. While this seems like a lot, I am not really concerned. I know neither the error rate of the radar gun nor the error in the velocity estimate of the GPS unit. The error inherent in both devices may be compounded. It is impossible to know without further testing.
• The radar gun may in fact be not too bad. After the first experiment I wasn't so sure.

Experiment #3: Velocity of a constant velocity car

YouTube Video

I experimentally determined the speed of my constant velocity car by timing it over a distance of two meters. I arrived at an average velocity of 0.157 m/s after three trials. With the radar gun set to scale speed (1/64) and kph I was able to get a reading of 35. Every time I did it I got 35 exactly. This converts to an actual speed of 0.15 m/s. If I use the 0.157 as the expected value I arrive at a percent error of 4.5%. I think that's Great!!!

Experiment #4: Real Velocity

Fresh off the constant velocity car I decided to try a real car. So I drove around the empty parking lot at my school and shot the light posts as I went by. I got the same reading as my speedometer every time.

Overall Conclusion:

The Hot Wheels Radar Gun works!!! At least for relatively constant velocity objects. I still need to determine how accurately it will measure velocity on an accelerating body. My feelings right now are it is worth the $30-35 spent, but only for measuring constant velocity. If you're planning on non-constant velocity this is probably not the tool for you.

For more Sneaky uses for free software and cheap tech toys, check out the FLOSScience Site.

Why FLOSScience?

The idea for this site has been percolating around in my brain since last year's NECC. Where I was presenting some of my Budget Probeware stuff in the Math/Science Playground. Someone recommended that I become the Open Source Science Guy since I was showing how to use Audacity to teach sound. Well, opensourcescience.com was already gone, so I bought FLOSScience.com. (FLOS = Free/Libre Open Source)

I like the idea of FLOS. Free in this case does not meant "no cost", but instead means the content can be used in nearly any way the consumer desires. I say nearly, because there is one caveat. If you incorporate my content in your work you must give me credit for my work and you must release your work under the same liscence. Basically, I'm just asking that you share your content in the same way I'm sharing mine.

So, what will you find here? Most of my stuff is aspected towards what I teach. So, it will mostly be physics and electronics. However, there will be other science stuff included as well.

Anyway, have a look around. In addition to this blog I have also set up a webpage (using Google Sites). The webpage is mostly a collection of posts from my old blog on technology in education, but new stuff will be appearing there as well. I'll be using this new blog to highlight new material as it appears on the site and to mention other cool stuff I find.

For the next week or two I will be posting once a day to highlight all the material that is already on the site. After this, my posting will probably become less regular.