Secular Science Resources for Homeschoolers



R2 Physics 26 – Seeing Color

Before class, students read 13.2 Discharge Lamps in How Things Work the Physics of Everyday Life and watched:

There are two different types of light ‘detectors’ on our retina, rods and cones.  Rods are very sensitive to low light but not to color, and cones are sensitive to different wavelengths (colors) of light.  Humans have three types of cones, one for predominately blue light, one for green and one more sensitive to red light (photo below).  Cones need fairly bright light so in low light conditions we are mainly detecting light with the rods, which is why we don’t see colors very well in dimly lit rooms.

Image from wikipedia

But not everyone sees colors in the same way.  Color blindness, or to be more accurate, color vision deficiency happens when one set of cones is not as sensitive as it should be. This is an inherited trait and affects men more often than women because the responsible gene lies on the X chromosome, which men only have one of and women have two.  Its unlikely for women to have the recessive gene on both of their X-chromosomes.  My husband is red-green color blind which means his vision isn’t as sensitive to red light, so a pink shirt might look white to him.  There are some great apps, including ColorDeBlind, that let you see what the world looks like with different color deficiencies.  The photo below shows how the fruit appears when you have ‘normal’ color vision and the photo on the right is what it looks like if your red-green color blind.  You can see the blue is pretty much the same but reds, oranges and greens all look like different shades of yellow and brown.


Animals can have different numbers of cones then us and they can cover different wavelengths or colors.  Some birds, fish and insects have 4 different cones, giving them tetrachromatic (4-color) vision.   Here’s a link to an article on color vision in animals in Cosmos magazine.

Unknown-1I happen to have a book of pseudoischromatic plates for testing color blindness where if you have ‘normal’ color vision you will see a number among the dots, but if you are color blind then you will not see any numbers, or you might see another number.  Enchroma, a company producing glasses that enhance the color vision of people with color vision deficiencies, has an online color vision test you can take for free here.

For the lab portion of the class, I did the colored flame demonstration, putting different chemicals (strontium chloride, lithium chloride, etc) over a butane burner and showed how they produced different colored flames.  Students looked at the flames with the handheld spectrometers and saw the light had different wavelengths.  The different chemicals produce different colored light because their energy levels are different and you can use a flame test to help identify chemicals. You can find a more detailed lab in this post from my chemistry class last year.

IMG_5312Students also did the color viewing box that I did with the middle school class a few weeks ago.  They made predictions for how different colored objects would appear under different colored light and then did the experiment to see if they were correct. We used different colored filters and a flash light to produce different colors of light.

Since this chapter also discussed fluorescence, I brought out our collection of fluorescent rocks and a shortwave Ultraviolet (UV) light.  The rocks look very boring in normal sunlight (photo on the left), but under UV light the rocks give off visible light.   The UV light excites the atoms in rock and when they relax to the ground state they give off visible light.  Just like the flames, the color depends on the elements involved.  The light I used was an old Raytech which doesn’t seem to be available anymore, but this one by UVP looks similar and is about the same price ($60) I paid for mine.  Not all rocks fluoresce but you can buy fluorescent rock collections online or buy them at local rock and gem shows.  You can read more about fluorescent rocks in this article.  This article also has some safety tips for using these UV lamps – they can damage your eyes and skin, so you need to make sure its only pointed at the rocks.


In class we watched a video on blackbody radiation by Physics Girl

and Why is Blue so Rare in Nature? by It’s Okay to Be Smart, which is a very cool video on how animals appear to be blue without using blue pigment.




R2 Physics 25 – Light

Students read Ch 13.1 Sunlight in How Things Work, the Physics of Everyday Life and watched the following videos before class:

At the beginning of class I lectured a bit on light, refraction and polarization, using my water tank of science (below) to demonstrate scattering and polarization.  The tank is filled with water and a bit of powdered milk to help scatter more light.  The flashlight is scattered by the powdered milk and scatters more blue light so when you look at the water near the flashlight it appears blueish.

But if you look at the flashlight through the the entire tank of milky water the light looks yellow… kind of like the sun, because the blue light has been scattered away leaving mostly yellow/red light to reach our eyes.  This is exactly why the sky looks blue during the day, the atmosphere is made of molecules that easily absorb and re-emit blue light but not the other wavelengths of light. During a sunset or sunrise the sunlight travels through more atmosphere since its coming in at an angle and the blue light is all scattered away by the time the light reaches you, making it look  red-orange and yellow.

Students measured the index of refraction of an acrylic cube (or other shape) by tracing the cube on a piece of paper and using one of the lightblox, trace the incoming and outgoing light beam.  The easiest way to do this is put two dots on the path and use a ruler to connect the dots.IMG_5239

Then connect the two light rays through the cube so you can see the path of the light.


Draw a dashed line perpendicular (normal) to the surface of the cube and measure the incident angle and the angle of the light inside the cube.


Once you have the two angles you can use Snell’s law to find the index of refraction of the cube.  The index of refraction of air, n1, is 1.00.  The cube is most likely acrylic so the index of refraction should be close to 1.49.


R2 Physics 24 – Electromagnetism

Students read 11.2 Electric Power Distribution in How Things Work the Physics of Everyday Life and watched Doc Schusters videos on magnetic induction and transformers.

In class we watched the following videos on how magnets are made and a SciShow on Tesla.

For the lab we made electric motors by making a small coil with magnet wire, stripping the insulation off the wire ends and placing in bent paper clips attached to a battery.  When the coil is placed on the paper clips it completes a circuit and electricity flows through the coil, which produces a magnetic field.  If you place strong magnets near the coil, it will spin as the magnetic fields interact.  The video below is from a class a few years ago.

We also made ‘the simplest electric motor‘ according to the Evil Mad Scientist website.  All you need for this motor is a battery, a strong neodymium magnet, a short piece of wire and a screw.  One of my students actually built a holder out of paper clips but you can just hold the battery with one hand, keeping one end of the wire in contact with the top end of the batter (doesn’t matter whether its the + or – end).  Attach the magnet to the head of the screw and touch the pointed end of the screw to the battery, it should hang there from the magnetic force of the neodymium magnet.  Now bring the other end of the wire to the SIDE of the magnet and it will set the screw spinning. IMG_5147

Unfortunately I did not get any videos of the spinning but there are some nicer photos and a video on the Evil Mad Scientist website, as well as description of why this works.  Below is their video on youtube.

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




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.

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