Secular Science Resources for Homeschoolers

SF Physics 20 – Blue Skies & Headless Polar Bears

This is one of my favorite topics to teach.  I’ve already written about the physics of why the sky is blue a few years ago so I’m just going to link to that old post.  6551371_origWe spent some time at the beginning of class talking about refraction and headless polar bears.  This is the same effect that causes your straw to look bent in a glass of water – the light bends different amounts when its going through air/glass/air (head of the bear)  or water/glass/air (body of the bear).  Its just more dramatic in the polar bear photo because the glass holding back the water (and the bear) is very very thick.

I like using this example below with a shopping cart to explain why light bends when it goes from one material to another. The cart is traveling on smooth pavement and going from bottom right to top left.  But when the cart encounters the grass it slows down.


The top right wheel hits the grass first so it slows down, while the other wheels are still on pavement and going at the faster speed, this causes the cart to change direction.  By the time all four wheels are on the grass, going the slower speed the direction of the cart has changed.   This is the same thing that happens to light waves as they cross from one medium to another.  In going from air to glass, the light slows down and changes direction.  How much it bends depends on the difference in the speed of the light waves in each material, hence light going from the polar bear’s head in air, through glass and back out in air, is bent a different amount than the light coming from its body which starts in water instead of air.

Science Fusion Module J has a lab, Refraction with Water that we did in class.  Students fill a beaker (a smooth clear glass would work fine) half way with water and observe a pencil and spoon when placed inside the beaker. Students notice right away that the pencil and spoon look bigger below the water line and they change the apparent size of the spoon by moving it inside the glass.  We talked about how the curvature of the beaker was acting like a lens and they did not see the magnification if they placed the spoon in the rectangular water tank since the sides are flat.   IMG_5111

The other Science Fusion lab students did was Comparing Colors of Objects in Different Colors of Light.  Last week, we had discussed why a blue ball looks blue – because it reflects blue light and absorbs the other colors (wavelengths).  So today I made a viewing box out of  shoe box – a whole to peek through and a hole in the top to shine a flashlight.IMG_5113

Students had to predict what four different colored objects, (white, black, red and yellow) would like under different colored light.  Then they put the objects in the box, one at a time, and placed a different filter (red, blue, green) over the hole in the box so the item was illuminated with red, blue or green light. The photos below show the view in the box for the yellow object. With no filter it appears yellow as predicted, but red light makes it look a bit orange, blue light makes it a teal color (according to my students) and the green light makes it a yellowish-green.  You don’t need fancy filters to do this experiment, you can use colored cellophane.  The point of this lab is to show that the apparent color of an object depends not only on the object but also on the wavelength of light that is shining on it.

We had a bit of time at the end of class and watched the following videos:


R2 Physics 23 – Magnets

For this week, students were asked to read Chapter 11.1 Household Magnets in How Thinks Work, the Physics of Everyday Life, and watch the following video by minutephysics.

I also reminded students they could be reading the Cartoon Guide to Physics, Chapters 12-19 for electricity and magnetism.

I started class with a bit of lecture about the previous chapter on electricity and then some on magnetism and how its similar (likes repel, opposites attract and the force depends strongly on distance) and how its different (you can have a postive charge all by itself, but so its impossible to have just a north pole, or just a south pole, they always come in pairs).

There were four activities involving magnets and magnetic fields for the lab.  1)  Use magnetic filings to observe and sketch the magnetic field lines of various magnets.IMG_5019

2) Build an electromagnet – wrap wire around an iron nail and then attach the wire to a battery and see if you can pick up paper clips with your electromagnet.  When students disconnect the battery the paper clips fall off the nail since its no longer magnetized.IMG_5006

3) Play Jishaku, a game where the first one to get rid of all their magnetic rocks win.  Students take turn placing the rocks in the blue foam pictured below.  The rocks are fairly strong magnets so if they are close enough the force between them will be strong enough to make them leap together.  If the rocks come together then you add them back to your hand.IMG_5002

4) Play with Magic Penny Magnet Kit and the bottle of ferromagnetic fluid.  The Magic Penny kit comes with two strong magnets (the silver bar below), some UK pennies and a book of tricks you can do with them.IMG_5015

I also showed the students an app, phET Interactive Simulations that is available on the App Store or Google Play and you can play with the simulations on your computer via a web browser.  They have a number of nice ones for electricity, including John Travoltage, Balloons and Static Electricity, Charges and Fields, Ohm’s Law, etc.  Its worth checking it out.  These simulations give students a way to ‘see’ and play with charges and fields and concepts that can be hard to get across since they aren’t easily visible. balloon phet




SF Physics 19 – Electromagnetic waves

We started the unit on Light (Science Fusion Module J) today with a slide show on the electromagnetic spectrum.  I actually found this slideshow (below), which I think may have been a student’s assignment and showed parts of it to my class as we talked about the spectrum.  I really stressed how these visible light, X-ray, radio waves, etc are all the same thing, and just have different wavelengths and frequencies.  I spent quite a bit of time discussing how the longer wavelengths means a lower frequency and shorter wavenlengths have a higher frequency but they are all traveling at the same speed, the speed of light.

We also watched this video, What is Light? by Kurzgesagt – In a Nutshell.

I have two simple spectrometers that came with a spectroscope analysis kit (one came with the kit and I bought an extra one) and had students look at red and blue LED lights (Light Blox light sources) and read off the wavelength of the light.  I also made the different colored flames with the different salts (potassium chloride, cupric chloride, lithium chloride, etc most of which come in the spectroscope analysis kit).


View inside the spectroscope shows the red light is roughly 650 nm.

When using the spectroscope to look at white lights or sun light reflecting off a surface (do NOT point it directly at the sun) you get a very nice rainbow of colors, showing that white light consists of all the colors (wavelengths) of visible light.

View inside the spectrscope when looking at sun light reflecting off a window sill. (Colored numbers were added to the photo since the scale is blurry in the photo)

You can see the spectroscope analysis kit in action with the colored flames in this older post from my chemistry class.  I’ve definitely gotten my money’s worth out of this kit and it came with enough chemicals that I’l be able to keep using it for many more years since you only use a few crystals each time.  There are instructions on line for making simple spectroscopes at home but none of the ones I’ve made work as nice as this, and the fact that this at least a rough scale for measuring wavelength is a big plus.

At the end of class, I had the kids fill out this electromagnetic spectrum worksheet that is available for free from Cloey Holzman on the Teachers Pay Teachers website.


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!

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.


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.

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.

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