Sadly, the school Science Fair is probably cancelled this year, but that doesn’t mean Junior can’t enjoy some exciting science experiments at home, such as the ones described 80 years ago this month in the April 1940 issue of Popular Science.

Actually, it might be a good thing that the official Science Fair is cancelled. It’s unlikely that the science teacher would sign off on these experiments, since they amount to playing with fire, and it would be hard to tie them in to the scientific method of inquiry. But they do have a redeeming scientific value of getting Junior excited about science, and they look like fun, as long as they are done in the backyard far away from any combustible objects.

The best experiment is shown above, where a line is traced out and then used as a racetrack for a race of fire.  A “pinch or so” of potassium nitrate (also known as saltpeter) is dissolved in a teaspoon of water.  This is used as ink, and the race course traced on a piece of paper.  When the paper is dried, the starting line is ignited with a “lighted match or cigarette tip.”  (Due to a pandemic of respiratory illness in progress, we advise against using a cigarette.)  Trails of fire then appear, racing to the finish line.  You can order the potassium nitrate at Amazon.

For the aspiring scientist who is interested in earthquakes, today we show you how to build your own seismometer. If you started by searching for “science fair seismograph,” you were possibly disappointed at the initial search results. You undoubtedly found sites showing how to make a toy seismosgraph out of materials such as cardboard boxes. I’m sure these were fine projects for less advanced students, but they weren’t real seismographs. Instead, they were models that showed how a seismograph worked. You build the toy instrument, and then jump up and down in close proximity, simulating an earthquake.

We are glad that you kept searching, because we will show you how to build a real seismometer or seismograph, one capable of detecting distant earthquakes.  If there are no earthquakes before the science fair, you can test the unit with nearby trucks and trains as they pass by.  The unit shown here, for example, picked up trains a mile away.  In addition, a very similar unit was used, in Texas, to detect underground nuclear tests in Nevada.  So it’s not a toy–it’s a real seismometer.

The overall concept is clear from the diagrams shown above.  A magnet is suspended from a wire or line attached to a sturdy beam of your building.  In the final version, this pendulum is placed inside a pipe, to prevent air currents from disturbing it.  The magnet is placed above a coil, and the slightest motion of the pendulum, caused perhaps by an underground nuclear test hundreds of miles away, induces a tiny electrical current in the coil.  This is amplified by two op amps, and registers with an LED and/or a piezo buzzer.

As shown in the diagram, the instrument is a seismometer, since it detects seismic activity.  To turn it into a seismograph, you will need to add some method of recording the readings continuously.  However, that is a very easy matter, thanks to a data acquisition module, similar to the one shown at left.  This is a very inexpensive device that hooks to the USB connection of your computer.  It has several inputs that you can hook to a circuit, and it continually feeds the measured voltage to the computer.  You can then use the computer to record the data numerically or in a graph.

All of the other parts are readily obtainable.  From Amazon, you can order the telephone pickup coil, the 741 op amp chips, and all of the other electronic components.  (For ideas on how to buy parts, see my crystal set parts page.)  All of the mechanical components should be available in any hardware store.

The diagram above is from a book by Forest Mims III, Engineer’s Mini-Notebook:  Science Projects, one of a series sold at Radio Shack.  This particular volume was published in 1990.  It’s available free online.  The same author has another version of the seismograph at this site.  You can also visit his website, forestmims.org.

Incidentally, as you can see above, the book contains the phrase, “when he was in high school in Texas, Eric Ryan Mims used a similar arrangement to detect underground nuclear tests in Nevada.” There is a multimedia CD by this long title by Canadian musician Matt Rogalsky. Inspired by that phrase, Rogalsky processed the output into ambient sound. While it is out of print, used copies are available on Amazon.

If Junior’s science fair project is due tomorrow, there’s plenty of time for him to take home the blue ribbon, as long as there is snow on the ground. The science teacher demands that the experiment answer a question, so Junior’s question will be: “Which melts faster–clean snow or dirty snow.”

It turns out that the dirty snow will melt faster. This is because the dark particles soak up heat, while the pure white snow reflects it. To prove it, Junior can set up the experiment shown above.

You will need a table lamp with an old-fashioned incandescent bulb. For this experiment, you do not want an “energy efficient” bulb. They are energy efficient because they generate less waste heat, but for this experiment, you want to generate heat. So the most inefficient bulb wins.

To accurately measure the rate of melting, the snow is placed on a piece of screen on top of a glass. There are two ways Junior can do the experiment. He can wait until all of the snow melts, and see which one melts first. Or, he can stop the experiment after a certain time and measure the water to see which one has more.

The teacher will be most impressed with Junior’s ingenuity. He or she will think that many weeks of planning went into it. Actually, 80 years of planning went into it, since the experiment appeared in the December 1939 issue of Popular Science.

Last month, we showed how Junior can win the science fair blue ribbon by making a hot-wire ammeter. That device, however, required a bit of precise construction, and the idea might not work if he hasn’t started yet and the project is due tomorrow.

Today, however, we have a project that can be put together in one evening, using parts that can be found around the house, or from the local hardware store. While not as precise, this meter also measures AC current. Today’s project is from 80 years ago, from the October 1939 issue of Popular Science.

The meter consists of nothing more than several turns of wire around a cardboard tube.  A piece of toilet paper tube will work well.  Like most old projects, the instructions call for bell wire, since this was readily available back in the day.  However, any type of insulated wire will work.  Because relatively high currents will be used, it should be a fairly thick gauge.  I would recommend buying a cheap extension cord, cutting off both ends, and then “unzipping” the two wires.

To make the project a bit safer, I would use another cheap extension cord cut in half.  The plug end  can be plugged in to an outlet strip and turned on when it’s time for the experiment.  This would allow you to cover all exposed wires with electrical tape.

After cutting this extension cord in half, splice one set of wires back together.  The remaining set of wires are connected to the coil.  The plug end goes to one terminal of the coil, and the socket end goes to the other side of the coil.  Into the socket, plug in an electric heater, which draws a large current.

Plug this in to the outlet strip and turn it on.  The heater should be running, and all of the current is passing through the coil.  Then, lower two iron or steel nails or screws on a string into the center of the coil.  Since they are magnetized with the same polarity, they will repel one another.  The higher the current, the further apart they are repelled.  You can demonstrate this by switching the heater from high to low.

It should be noted that today’s project involves household current, and care must be taken not to touch any exposed wires, since contact could prove fatal.

Seventy-five years ago this month, the August 1944 issue of Popular Science showed a number of simple science experiments relating to the Earth’s magnetic field. For students looking for a simple science fair experiment, these will prove most adequate. The two shown on this page answer the question, “does the Earth have a magnetic field?” It turns out that yes, yes it does.

Magnetizing the needle.

The first experiment produces the compass shown above that is, as the magazine puts it, as good as the best that was known for centuries. All you need is a sewing needle, a magnet, a cork, and a cup or glass (non-metallic) of water. You magnetize the needle by stroking it over the south pole of the magnet, starting at the eye and ending at the point.

If you get that mixed up, it doesn’t really matter, as one end will point north, although it might not be the pointy end. Either way, you’ve proven that the Earth has a magnetic field.

The other experiment, shown at left, uses the Earth’s magnetic field to magnetize an iron rod. You hold it so that it’s pointing north, and to maximize the magnetic field, you angle it down toward the ground. Tap the upper end with a hammer, and the atoms will align with the magnetic field. You can test this by bringing an end near a compass, either the one you made yourself, or one you bought.

You probably have most of the supplies you need for these experiments around the house, or they are available locally.  The links above are to Amazon.  The links are affiliate links, meaning that this site receives a small commission if you order after clicking on them.

If you’re looking for an interesting science fair project, this one from the August 1939 issue of Popular Science is interesting, looks like you put a lot of work into it, but is really quite simple. It answers the scientific question, “does the temperature of an electrolyte solution affect the conductivity?” It turns out, as this experiment will show, that the answer is yes. As the temperature increases, so does the conductivity.  (Or to put it another way, as the temperature goes up, the resistance goes down.)

The experiment, as shown above, is relatively simple.  You should be able to find all of the required supplies locally (if you don’t already have them at home).  If you want to order online, the links below are to Amazon.

The 1939 version of the experiment shows old fashioned dry cell batteries, but modern alkaline D cell batteries will work just fine.  You can figure out some other way to attach the wires to the batteries, but life is a lot easier if you use a battery holder.

Any flashlight bulb will work, as long as it’s from a flashlight that normally uses 2 batteries.  This one is suitable.  Again, you can figure out some other way to connect the wires, but having a socket will make things easier.  Finally, for the electric hookups, you will need some kind of wire, although almost any will work just fine.

The two electrodes going into the solution can be almost anything metallic.  I would recommend using some large nails.

You’ll need a beaker and some lab hardware to support it while heating, although if you should be able to borrow that from your science teacher.  If you’re doing the experiment in the school lab, you can use a bunsen burner.  If you’re doing it elsewhere, you’ll need a heat source such as an alcohol burner.

The experiment calls for either salt water or sulfuric acid.  You surely have salt at home.  If you prefer to go with sulfuric acid, you can order that online, or ask for it in the hardware store, where it’s available as a drain cleaner.