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Secular Science Resources for Homeschoolers

R2 Physics 22 – Electric Fields and Circuits

Students were asked to watch the following videos and read 10.3 Flashlights in How Things Work the Physics of Everyday Life.  We skipped over 10.2 Xerographic Copiers.

In class, we watched this video on tesla coils because one of the students brought in a small tesla coil that he had built when he was 8!

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Homemade tesla coil

For the lab we took a look at electric fields by pouring some mineral oil (non-conductive fluid) in a petri dish and sprinkling lettuce seeds on top.  We had pieces of a metal clothes hanger bent in different shapes to be our electrodes.  One electrode is grounded (touched by a student) and the fun fly stick is used to build up negative charge on the other electrode.  We placed a bit of aluminum foil over the end of the wire to collect more charge.  The styrofoam cups in the photos are just used to prop up the electrodes and keep them isolated. The two electrodes end up with opposite charge and the seeds will move around and align themselves to the electric field.  This is kind of similar to sprinkling iron filings over magnets to see magnetic fields.

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Students used the circular shape above and two straight electrodes.  They also moved them and observed the electric field getting stronger when they brought the metal electrodes closer together.  One group found the force was so strong that they could move one electrode across the petri dish by moving the other one.

IMG_4888I also brought out my snap circuits and let the students build circuits.

If you’re looking for one long video on electricity the Royal Institute has this one, Zap, Crackle and Pop: The Story of Electricity, which is full of nice demonstrations.

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SF Physics 18 – Speed of Sound

We started class with the following videos on sonic booms, SONAR and echolocation.

We played around with the free app, SignalScope X by Faber Acoustical.    The app uses the microphone in your phone or iPad and displays the sound waves on the screen like an oscilloscope. Below is a waveform that I made by humming a note.  You could use this app to measure the period (T) of the wave, time between crests or troughs and then calculate the frequency (1/T).  For the wave shown the period is roughly 5ms (0.005s) and frequency = 1/0.005 = 200 Hz. We used it to look at sound waves produced by the tuning forks.  IMG_5087.png

While searching for labs  I found a video of the speed of sound lab that I did with the IMG_4898high school class, but they were using wider tubes and the resonance was much easier to hear, so I repeated that experiment with the middle school class using the boom whacker tubes and it worked much better. Since the tubes were so much wider we had to use big plastic containers to hold the water instead of graduated cylinders.  When you move the tube up and down with a tuning fork over the opening, you will hear the sound get louder when the length of the tube, L, is equal to 1/4 of the wavelength of the sound. Students found resonance (the length where the sound got louder) for four different frequencies (tuning forks) and calculated the speed of sound for each one ( speed = wavelength x frequency).  They all found values close to 330 m/s.

Here’s the video of tuning forks demonstration, the speed of sound demo is around 3:20.

SF Physics 17 – Field trip!

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This week both my physics classes went to the Tech Museum in San Jose for a class on roller coasters and to check out the Body Worlds Decoded exhibit.  The class started with a short lecture on roller coasters with a lot of class participation and then students had 10 minutes to build a short roller coaster.  After some more discussion on roller coasters and energy the students were asked to build roller coasters with a loop!  If they succeeded  with time to spare they were given a challenge card (2 loops for example).  As you can see in the photos, this was done with pretty inexpensive equipment,  foam hose insulation cut in half for tracks and whatever building toys (tinker toys in this case) you might have, masking tape and a marble.  Classes like these at museums are great, I’ve never been disappointed.  The Tech Museum field trips are a great deal, only $5 per kid and chaperones were free, we got the 90 minute class, free IMAX film and got to wander around the museum afterwards.

The Body Worlds exhibit was pretty cool as well, may have to go back next year when we’re doing biology since I believe its going to become a permanent exhibit.

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R2 Physics 21 – Static Electricity

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For today’s class students read 10.1 Static Electricity in How Things Work, the Physics of Everyday Life and watched the following videos.

The night before class I tried to get this lab with packing peanuts to work but I suspect the peanuts I had were designed to be anti-static because I could not get this to work.  Here’s a link to the lab  on Harvard’s website if you want to try it.  I asked students to bring in some packing peanuts and we strung some up and were able to at least use them  to detect static electricity but we didn’t make any measurements.IMG_4788

Today was mainly a play with static electricity day.  We had balloons, PVC and acrylic rods, little bits of paper and tinsel, a variety of fabrics, including rabbit fur and the students experimented to find the best way of charging up things and zapping their neighbors.  There was one lab with specific direction using scotch tape (activity 1-4 of this handout from University of VA) but otherwise I let the students have fun.

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One group discovered that if they wrapped some aluminum foil over the fun fly stick, enough charge would build up to produce a spark when they brought a finger near it.  Here’s a slow motion video of the some of the ‘finger lightning’ they produced.

I highly recommend the fun fly stick, its relatively cheap and a lot of fun.

 

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R2 Physics 20 – Sound

doppler ball

The high school class is also doing sound this week so I had the tuning forks and salt and water out so they could do the same demonstrations as the middle school class did yesterday.  I also brought out the doppler ball, a tennis ball with a buzzer and 9V battery inside it.  When a student swings it around the other students hear the doppler effect, the buzzer sounds higher in pitch as its moving toward you and lower in pitch as it moves away.

I spent sometime at the beginning of class showing the animations of this website by the Dept of Physics & Astronomy at the Appalachian State University, that I think do a really nice job of showing how sound waves travel through air.  One of their animations is below.

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The gray line on the left is a vibrating string and you can see how when it moves to the right it causes the air molecules to bunch up (compression) and when it moves back to the left  they spread out (rarefaction).  At first glance it looks like the molecules continue moving across the screen but they are actually vibrating back and forth.  Watch one particular atom and you will see it move to the right and then back again. They have colored 3 of them red to help you see this.   If you go to their page and scroll down to Activity 3, they have some nice animations showing a standing wave in a closed tube, which is exactly what the students did in the lab today.

IMG_4666.jpgWe used a clear plastic tube, open at both ends and placed one end in a graduated cylinder of water, making it a tube with one open end and one closed end (water effectively closing the bottom of the tube).  As you move the tube up and down in the water you change the effective length of the tube.  Students struck a  tuning fork and held it over the top of the tube and moved the tube up and down, listening for the sound to get louder.  When the length of the tube is equal to 1/4 of the wavelength of the sound wave, you have resonance and set up a standing wave in the tube, which makes the sound louder.  When the student finds resonance, they measure the length of the tube and calculate the wavelength.   They can record the frequency of the tuning fork (they are labeled with their frequency) they used and multiple that with the wavelength to calculate the speed of sound = wavelength x frequency.  All four groups found the speed of sound to be around 320 m/s, which is a little lower than the expected value of 340 m/s. We talked about why their answers might be too low.  The difficulty in finding the right length and holding the tube still while measuring it with the ruler were the most likely cause.  To get a higher value for the speed of the sound we should have gotten longer wavelengths, hence longer tube lengths and its reasonable to assume if anything the tubes dropped a bit more into the water between finding resonance and measuring the length.

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