Magnetism (6)
Electromagnetism (5)
Electrochemistry (5)
Radio (6)
Thermodynamics (8)
Aerodynamics (3)
Light and Optics (12)
Biology (5)
Mathematics (3)
Computers and Electronics (4)
Building simple heat engines.
Hero's steam engine.
A simple steam engine powered boat.
A simple rotary steam engine.
An engine driven by the heat of your hand.
A bi-metal strip heat engine.
A simple solar powered heat engine
A simple rocket engine you can build in your kitchen.
Building a Film Can Cannon.
A metal that melts in hot water.
Liquid metal at room temperature.

Building simple heat engines.

Heat engines take many forms, from the internal combustion engine in the family car to the giant turbines that generate electricity for our homes. What they have in common is they steal some of the energy moving between something hot and something cold, and convert it into motion. When you heat a gas like air or steam, the molecules in the gas move around faster. The faster they move, the harder they hit anything that is in the way. If we put something in the way, such as a propellor or a pinwheel, we can make them spin (this is how turbine generators spin to create electricity). If we confine the gas in a container with a lid, we can pop the lid off (this is how the engine in a car works). If we let the fast moving molecules push on one side of a container, and escape through a small hole on the other side (so they are pushing on one side more than on the other) then we have a rocket or a jet, which moves in a direction away from the side with the hole. In this chapter we will make a working version of the first heat engine (a form of steam turbine), a gas turbine engine that runs from the small heat difference between your warm hand and the cooler air around it, and some tiny rockets that can be made in the kitchen in a couple minutes, and then shoot across a driveway.

Hero's steam engine.



Why does it do that?


Why is the steam cool when it comes out?


The worlds simplest steam powered boat

This next toy is an example of the simplest steam engine you will ever see. It has no valves, no moving parts (in the traditional sense of the phrase), and yet it can propel it's little boat easily across the largest swimming pool or quiet duck pond. The photograph above tells nearly all the construction details. The boat is a plastic bottle, cut in half lengthwise. I used a soft plastic bottle that contact lens saline solution comes in. It is made of white High Density Polyethylene (HDPE), and is very easy to cut using an Xacto knife or other sharp utility knife. Near the bow of the boat is a small candle, such as those used to keep food warm on the table. I chose a candle that comes with a small aluminum can, and is less than an inch high, so it would sit low in the boat and not drip wax all over. The aluminum cup keeps the melted wax in place, so the boat can go for hours. I used a small amount of sticky tape to keep it in place. The engine is made of 1/8 inch soft copper tubing. This can be found at the better hardware stores, and is normally used in refrigerators. You can use the easier to find 1/4 inch soft copper tubing, but the 1/8 works best with the candle's small heat source, and weighs less, so it is less likely to tip the boat. The best way to cut the tubing is with a tubing cutter (get it at the hardware store when you get the tubing). You can use a hacksaw, but you will have to clean the debris out of the cut with a knife or sandpaper. Gently bend the tubing around a large pen or pencil (I used the handle of a wooden spoon) to form the coil in the center. Poke two holes in the back of the boat with a nail, and force the copper tubes through the holes. The holes in the soft plastic will close around the tubing, forming a water-tight fit. It is also possible to simply lay the tubing on the top of the back part of the boat, and then bend it down so the ends are under water, and pointing to the rear. Gently bend the tubing so the coil is just above the top of where the candle flame will be. The boat is now finished, and ready to launch. The copper tubes must be full of water, and both open ends must be under water. The easy way to fill the tubes is to hold one end under water, and suck on the other end. When the tubes are full of water, and the boat is resting in the water with both ends of the tubing under the water, light the candle. When the coil of copper tubing is hot enough to boil the water inside, the boat will jerk ahead suddenly, then start moving evenly forward. If you put your fingers in the water just behind the tubes, you can feel little pulses of water, about 5 or 10 pulses per second. These pulses are pushing the boat along. In the photograph above, the candle has been replaced with a lump of charcoal starter cake. This makes a bigger flame, and makes the boat move even faster. The candle is safer, however. In the photograph you may be able to just barely see the ripples in the water behind the boat. These ripples are caused by the 5 to 10 pulses per second that the engine makes as it operates. The easiest way to view this is to watch the reflection of a bright light on the surface of the water.

How does it do that?

Click on photo for a larger picture These are made in India on hand-operated presses, from tin plated steel. They are then hand-painted. They make a wonderfully loud "putt-putt-putt" sound as the steam around a bathtub, swimming pool, or pond. They come with a tiny candle, and also a little wick so you can use olive oil as a fuel, which will run the engine for hours. You can click here to see a video (with sound) of the little boat speeding around a bathtub. The video is 1,348,276 bytes long, and will take a little while to download, so be patient.

A rotary steam engine

We can use the same steam engine that pushes the boat in a different way. We can arrange that the engine causes something to turn. We start with an aluminum soft drink can, which we cut about a third of the way up from the bottom to form a small cup. We then carefully (so as not to cut our fingers) bend over the sharp edge, and crimp it with a pair of pliers to form a neat edge. Don't worry too much about neatness, since it will not affect the operation of the engine, only the looks. We also put a large dent in the bottom of the can, which is normally bowed up in a dome, which is inconvenient, since we want to put a candle there later. We punch two neat holes in the side of the can, opposite one another, with a paper punch. These holes will hold our copper tubing. Next we put in the candle, using the same kind of candle (with its convenient little cup to hold the melted wax) as we used for the boat. Around the candle, we put a rope of crumpled aluminum foil, to keep the candle centered in the can. Now we make the tubing coil in the same way as we did for the boat. This time, however, we bend the ends out to fit through the punched holes. This is a little tricky to do at first, but you soon get good at it. In the version shown, I have added an extra coil to the engine, but this is not necessary, and does not improve the engine. Next we bend the ends of the tubing gently so they curve into a right angle. Each end is bent opposite the other, so the can will spin when it is placed in the water and the engine started. The final photograph shows the engine in operation. With a candle, it spins at about one rotation per second.

A simple rocket engine you can build in your kitchen

There is a fascination about rockets that delights children and adults alike. The arc of smoke, the idea of flight, and the fun of action at a distance combine to make rockets a wonderful toy. To these pleasures we will add the forbidden glee of playing with matches, and the satisfaction of learning how something magical actually works. Unlike most of the rest of this book, this really
is rocket science. The rockets we are about to build are perhaps the smallest toys in this book. They travel about ten feet, which is nonetheless 150 times their length. They are hot to the touch, and can blister a hand that catches them, so care must be used to fire them only outdoors, on a fireproof surface such as a driveway. Since they are notoriously inaccurate, the center of the driveway is suggested, so they don't land in dry grass somewhere. As always when playing with things that burn, a source of water such as a bucket or garden hose should be nearby in case of accidents. These rockets are made out of aluminum foil and match heads, and take less than a minute each to manufacture. You will need a book of paper matches (or a box of wooden matches), a sheet of aluminum foil, a pair of scissors, a paper clip, and a straight pin. Start by cutting a narrow strip of aluminum foil, about 1 inch wide and three inches long. Tear the head off of a paper match (or cut it off with the scissors), leaving as little of the paper as possible attached to the matchhead. Set the matchhead on the foil near one end, with the top of the head facing down towards you. Roll the edge of the foil over the matchhead, forming a tube with the matchhead firmly in the center. Unfold the paper clip and insert one end of the wire into the tube so it touches the top of the matchhead (not the paper). Now press the foil tube flat to hold everything in place. Fold the foil over one more time (or twice if you like), and tear off the excess foil. Now twist the foil at the free end tightly (without tearing it). Twist the end with the paper clip tightly around the paper clip, keeping the wire touching the matchhead at all times. Lastly, cut off the excess foil from the top of the rocket (the end away from the paper clip). We are now finished with the rocket, and we are ready to build the launcher. The rocket launcher is a straight pin stuck through a piece of cardboard (such as an empty matchbook) or a wad of aluminum foil. The pin should point upwards at a 45 degree angle. The rocket is removed from the paper clip, and slipped over the pin, so the pin is now where the paper clip used to be. To launch the rocket, first aim it in a safe direction, where it won't start a fire or melt anything it hits. Then light a match, and hold it under the rocket. The heat of the flame will cause the matchhead to catch fire inside the foil. The hot gases from the matchhead will have only one way to escape -- through the hole where the pin is. As the gases go one way, the rocket goes the other, with a sharp hiss, and a trail of smoke. Depending on how big the matchhead was, and how much foil was used, the rocket will travel anywhere from a few inches to 20 feet. If your rocket does not fly, but instead bursts through the side of the foil, you need to build one with more foil (by rolling it one more time before tearing off the excess foil). If it hisses but doesn't leave the pin, check to make sure that the rocket slides easily up and down the pin. The pin should not block the tube completely, but should leave some space between it and the foil. In other words, the pin should be skinnier than the paper clip. Be careful not to squash the tube flat while handling the rocket.

How does it do that?

A matchhead makes a good rocket fuel because it carries both the burnable material and the oxygen needed to burn it. The burnable material in this case is the sulfur in the matchhead. The oxygen comes from compounds like potassium chlorate and potassium nitrate that are mixed with the sulfur. When the matchhead is heated, the sulfur and the potassium chlorate combine to make sulfur dioxide gas, and potassium chloride. This generates a lot of heat, which heats up the gases. The hot gases are under a lot of pressure, and their molecules hit the walls of the rocket at great speed. Where the nozzle of the rocket lets the gases out, there is no wall to hit, so there are no molecules pushing in that direction. The difference in pressure between the nozzle end (no pressure) and the opposite end (high pressure) is what pushes the rocket forwards. Next: More thermodynamic toys... For more information on thermodynamics, see the Recommended Reading section. Order steamboat toys here.

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