Seventy-five years ago this month, the June 1943 issue of Popular Science showed how to do this seemingly impossible balancing act. The hammer is suspended by a string in the middle, with the end of the handle exerting an upward force on the end of the ruler. Since the center of gravity is under the table, the ruler stays in place.
This simple stunt could be the basis for an elegantly simple science fair project regarding leverage.
If you’re reading this page because Junior just remembered that the science fair project needs to be handed in tomorrow, there’s no need to panic! This site is full of interesting science fair projects. Some of those projects might take some time to complete, but many of them can be whipped into shape in an evening. This one falls into that category. Junior can make an impressive display by mapping magnetic lines of force.
If the project is due tomorrow, have Junior start reading the Wikipedia article about magnetic lines of force. In the meantime, you can race to the hardware store or dollar store to get the items he’ll need, if you don’t have them already.
First, you’ll need some insulated wire. Any kind of wire will work, as long as it’s insulated. At the dollar store, you can probably find it in the electronics aisle in the form of speaker wire. Get about 10-20 feet.
You’ll also need a battery. The old-fashioned dry cells shown above look nice, but there’s really no need. Normal D-cell flashlight batteries will work just fine. Get a few extras, since they will be used up quickly.
Finally, you’ll need a cheap compass. If you don’t have one already, you can probably find one in the toy department, and it will work fine. And while you’re there, don’t forget to get the obligatory poster board, markers, etc.
Have junior construct the loop of wire shown in the picture, and embed it in a piece of cardboard. Hook the ends of the wire to the battery, and you have created an electromagnet. Simply move the compass around the cardboard, and with a pencil, make a small mark showing what direction the compass is pointing. Connect all of these marks, and you will have an accurate diagram of the magnetic lines of force.
The teacher will be impressed, Junior will get a blue ribbon, and nobody will know that he waited until the last minute.
You can find more details in the March 1943 issue of Popular Science, from which the illustration was taken.
One item that was in short supply 75 years ago were meter movements. There was a backlog in their manufacture to the point where hams were being encouraged to sell their old ones, as shown from the form at left from the April 1942 issue of QST.
But the absence of a meter didn’t have to mean that it was impossible to measure things. The device shown above was a simple bridge circuit for measuring the values of resistors, capacitors, and inductors. The circuit was contained in an article in the March 1943 issue of QST, submitted by W.J. Mertz, VE4UN, using whatever was available. An audio signal is fed into the input, and the potentiometer adusted until the circuit is in balance, at which point the audio output disappears. By calibrating the dial with a few known values, the unknown value can be quickly determined.
The author didn’t have an audio oscillator, so he instead used the device by feeding in the squeal from a regenerative receiver. And in the absence of anything else to make the dial pointer, he used the handle of a broken toothbrush.
Tired of the bother and expense of having to buy batteries for his radio, the gentleman shown here is taking matters into his own hands by constructing a B-battery eliminator, following the plans in the March 1928 issue of Popular Mechanics. We showed a 1926 version earlier, and this one is more refined.
In this case, hum is dealt with by electrolytic capacitors, which were available for purchase. Rectifiers, on the other hand, weren’t as easy to come by. But undaunted, he just made his own, consisting of plates of lead and aluminum carefully suspended in pickle jars containing an electrolyte solution. That solution could be borax, sodium bicarbonate, or ammonium phosphate.
The rectifiers were just a bit tricky to get going, which explains the light bulb in series with the transformer primary. If the rectifiers were doing their job, the lamp would light briefly and then dim. If the light remained on, it meant that one of the cells needed attention. In either case, the light bulb served to limit the current and protect the expensive transformer.
Since modern rectifiers are so inexpensive, there’s little practical reason to make your own. However, they’re so simple to construct that a homemade rectifier would probably be the basis of an excellent science fair project for the advanced student.
Fuller and the Dymaxion map.
Seventy-five years ago today, the pages of Life Magazine, March 1, 1943, included a craft project, in the form of a Dymaxion map of the world. A flat map of the round earth is always distorted, in either scale, direction, or shape. For example, the familiar Mercator projection accurately shows direction, but scale is greatly distorted close to the poles, which explains why Greenland looks much larger than it really is.
The Dymaxion map, designed by R. Buckmisnter Fuller, seeks to compromise to make all of these distortions as minimal as possible. It is a cube with the corners cut off, and is formed from six squares and eight triangles. The transformation from a round globe to a flat map is shown in the animation at right.
The magazine contained all of these sections, some of which are shown above, with instructions for pasting them to cardboard and assembling them. When assembled, they could be laid out flat in various configurations, or put together completely as a squared-off globe. For those wishing to duplicate the 1943 globe, it would be an easy process to print the pages on cardstock and assemble them following the directions. (You can download the magazine at this link,)
An interesting science fair project could be made comparing a globe, a Mercator projection, and the Dymaxion projection.
Seventy-five years ago this month, the February 1943 issue of Radio Craft showed how to make this rudimentary photovoltaic cell.
With some modification, it scould be easily duplicated today, and could be the basis for an interesting science fair project.
It consists of a strip of lead, as well as a copper plate covered with cuporus oxide. To achieve the coating, the copper plate is heated in a flame until it is covered by a black flaky substance, which is cupric oxide. Then, it is washed in a weak solution of ammonia, which reveals the light-sensitive cuprous oxide.
A sheet of lead should be available at a craft store, or can be ordered from Amazon. Similarly, a small piece of copper is readily available at a hardware store or Amazon.
The electrolyte is a somewhat more difficult proposition. The lead nitrate is somewhat hazardous, but should be safe if handled carefully. The main problem is that it is expensive. It is available on Amazon, both as a solution and as crystals, However, the prices might be outside the young mad scientist’s budget.
Fortunately, this site seems to suggest that ordinary salt water will function adequately as the electrolyte. Therefore, one suitable science fair project might be to determine what other electrolyte solutions might work best. All that would be required would be a voltmeter to see which configuration puts out the most electricity. The advanced student could skip buying the voltmeter and instead make this simple galvanometer.
Another fun project would be to demonstrate communication over a light beam, with a setup similar the one on this site. Your homemade photocell is hooked to the input of a small audio amplifier, and you hook an LED to the headphone jack of a radio or other audio source.
This illustration of a handsome crystal set listening post comes from 90 years ago, in 1928 issue number 1 of Радиолюбитель (Radio Amateur) magazine, illustrating an article by A. Pushkov.
Elsewhere in the magazine, it’s apparent that, just like their Western counterparts, young Soviet experimenters discovered the fun that could be had with a milliammeter, although I have to admit that I never thought to conduct the second and fourth experiments shown here:
(The piece of metal in the above diagram is marked “железо”, iron.)
The sensitive galvanometer was probably a valuable instrument in the 1928 Soviet Union. Modern students desiring to reproduce these experiments can do so very inexpensively with a digital voltmeter such as the ones shown here:
I’m not able to make out the text, but this Soviet magazine from November 1967 appears to be right up our alley. It appears to be giving young comrades instructions for building a home blast furnace!
I am able to make out the caption for the item between the vacuum cleaner and the wall outlet, and it’s marked “rheostat.” Presumably, it’s set to blow air into the combustion chamber, and the young Soviet mad scientist can adjust the intensity of the furnace with the rheostat.
The illustration appeared in the November 1957 issue of Юный техник magazine. A treasure trove of similar magazines, many on the subject of radio, can be found at Журналы СССР.
Contrary to first impression, the logo at the top of the page is Ют, the abbreviation for the name of the magazine. But if it looked like HOT at first glance, we don’t blame you. This contraption will indeed get hot!
We put this item in the “science fair ideas” category. However, we do recommend that before duplicating this project, young scientists should have the article translated to see if it contains any safety warnings. I suspect some might be called for.
With it being unfairly accused of responsibility for many a UFO sighting, the humble substance known as swamp gas today has an undeservedly bad reputation. But this was not the case for this gentleman using swamp gas as part of his scientific inquiry, following the plans set forth in the November 1937 issue of Popular Science, in an article with the title of “Fun With Explosive Gasses.” With a title like that, you can bet that it’s going to appear on these pages. The article notes that hydrocarbons can be the subject of many spectacular experiments by the amateur chemist, and details a number of explosively good experiments.
The article begins tantalyzingly with some of the possibilities:
Would you like to get gas from coal without heating the coal? To make an inflammable gas that will dissolve in certain liquids as easily as sugar does in coffee? To produce a gas that burns with a flame you can hardly perceive? Or to create fiery bublles of gas, jumping about like grasshoppers, from simple everyday chemicals? These are some of the curious and interesting experiments with hydrocarbon gasses that any amateur chemist can easily perform.
The gentleman in the illustration is collecting methane, the gas that bubbles up through the water of marshes. He is collecting it by stirring up the muddy bottom and trapping the ascending bubbles under an inverted funnel.
For those without a nearby swamp, the article also explains how to mix up a batch in the lab.
The article also explains how to make acetylene. This involves first creating some chlorine gas, capturing it in a bottle, and then adding some calcium carbide and water. As the resulting acetyline reacts with the chlorine gas, it produces a flash of light and a tiny cloud of soot. “With the bombardment proceeding at the rate of several explosions a second, the bottle resembles a miniature battlefield.”
For the aspiring young mad scientist, this article should be great inspiration for a first-place science fair project.
Seventy years ago, the October 1947 issue of Popular Science showed this method of making sure your watch was accurate.
While this method would not, by itself, give you the exact time, it would very precisely tell you the elapsed time.
The method was very simple. You simply installed a piece of tin with 1/16 inch hole on some fixed location, such as the side of the building. You used it to sight a vertical fixed object, such as a lightning rod or distant skyscraper. Then, you observed the exact time that any star was occluded by the object. Since the star is essentially a point of light, it would disappear suddenly. You noted the time.
Then, the next evening, you would observe the same star. It would be occluded exactly 23 hours, 56 minutes, 4.09 seconds later–one sidereal day. In other words, the time on your watch should read exactly 3 minutes 55.91 seconds before the previous night’s figure. (For all practical purposes, a sidereal day is 364/365 of a solar day. This makes sense, since the Earth itself has moved 1/365 of its way around the sun in 24 hours.)
Depending on whether your watch was fast or slow, you could thus adjust the spring.
If you knew the exact time the first night, then you could also create a table showing the exact time of occlusion subsequent nights. As long as you didn’t move the piece of tin, you would always know what time it is.
This method has two applications. After the zombie apocalypse, presumably WWV will be off the air. The stars give you a method to keep your clock calibrated very accurately. It could also be the basis for a very interesting science fair project.
