Stomp Rockets, Catapults, and Kaleidoscopes
30+ Amazing Science Projects You Can Build for Less Than $1
By Curt Gabrielson
Chicago Review Press Incorporated Copyright © 2008 City of Watsonville
All rights reserved.
HOLIDAY LIGHT CIRCUIT
A9-volt battery will light these tiny bulbs, if you hook them up right.
The Basic Concepts
Electricity has to have a complete path in order to travel from one side of a battery to the other. This path is called a circuit. A switch "breaks" — or opens — the circuit and stops the electricity flowing. A battery "pushes" the electricity around the circuit. When the chemical reaction within the battery runs out of chemicals, the battery is dead and can't push anymore.
Glue a film canister to the middle of one edge of the baseboard. Cut a paint paddle to be about 9 inches long. Glue a craft stick to one end of the paint paddle.
Glue the other end of the paint paddle to the edge of the baseboard and also to the film canister. Glue the other film canister on the opposite edge of the baseboard, as shown.
Strip the insulation off both ends of three 8-inch wires. Strip both ends of the holiday light wires. Connect one 8-inch wire to each end of the holiday light wires. One of these wires will go directly to the battery, the other to the craft stick.
Drape a second 8-inch wire over the craft stick and wrap it around once. Tie the weight to this wire near the bottom. Wrap the third 8-inch wire around the paint paddle and make a loop that encompasses the hanging wire. This wire will go directly to the battery. These two wires need to be stripped about 5 inches from one end. When the hanging wire swings, it should contact the loop wire.
Put a battery in the film canister near the paint paddle. Use a 9-volt battery snap if you have one. If not, connect one paper clip to the loop wire and one to the wire coming from the lights. Connect the paper clips to the battery snaps, taking care not to let them touch each other. When you're finished, there should be a single series circuit: from one side of the battery, to the holiday lights, to the swinging wire, to the loop of wire, and back to the battery.
Draw a picture of a snowman (or whatever you'd like) on the file folder or thin cardboard and cut it out. Make a hole in the picture with a screwdriver for each light. Each hole must be big enough to hold the light firmly. Insert the lights, and glue them in place if they do not stay by themselves.
Glue the figure to the front film canister.
Add craft sticks for rigidity if it does not stand up on its own. Swing the weight back and forth. The lights will flash every time the dangling wire touches the loop completing the circuit.
More to Think About and Try
* What happens when one light goes out?
* If you put more lights in the circuit, would they be brighter or dimmer?
* How could you make it blink longer?
* How could you make it blink faster?
A Little Background
Wire is the conductor through which the electricity travels in this circuit. Air, on the other hand, is a pretty good insulator. So when the weight is swinging and the wire is not touching the loop, electricity does not travel through the circuit. This is known as an open circuit and is exactly the arrangement in a light switch when you shut off the light.
When the wire holding the weight touches the loop wire, the circuit is complete and electricity can travel through it. The lights glow. This is called a closed circuit.
If you happen to cross the two bare ends of the holiday light wires, the lights will go out but the battery will continue pushing electricity around a circuit. Since there are no lights and just wire in this new circuit, it is smaller, that is, shorter, than the one you had before you touched the wires. This situation is called a short circuit.
The lights that went out when you shorted them had some resistance, which limited the amount of electricity that could flow through them. When the circuit is shorted, this resistance is gone and much more electricity can travel around the circuit. In this project the worst that will happen with this type of short circuit is that the battery will get warm and go dead rapidly. However, if the battery was much bigger and could supply a lot of electricity, this would be a dangerous situation. The wires or other components of the circuit could become hot and perhaps explode. This is why homes have fuses or circuit breakers. Both of these instruments open a circuit that suddenly has too much electricity traveling through it, usually due to a short circuit.
Electric circuits come in two varieties: series and parallel. Try taking one lightbulb in a string of holiday lights out of its socket. The other bulbs should go out. Bulbs in a series circuit act this way. The electricity goes through each bulb, one by one; if you take one out, you have opened the circuit. Bulbs wired in series have to share the total voltage of the circuit. For this reason, you can use these lightbulbs with a 9-volt battery when they were designed to be used with a 120-volt wall outlet. You used only two or three, whereas in their original circuit, there were perhaps 50 bulbs sharing the 120 volts.
You can also wire holiday lights in parallel — try it! Set it up like the drawing on p. 5. Cut two lightbulbs out separately and strip the wires on either side of them. Connect one wire from one bulb to one wire from the battery, and then connect the other wire from that bulb to the other battery wire. That bulb should light up. Then connect one wire from the other bulb to one of the connections you just made and the other to the other. Both lights should now glow.
Now try removing one bulb. The other should stay lit. This is because each bulb has its own path in a parallel circuit. Each type of circuit has its advantages. You may notice that the bulbs wired in parallel glow more brightly. This is because they each get the full voltage of the battery. On the other hand, they'll use more electricity and the battery will go dead sooner.
In a series circuit, if you have fewer lights, each will shine brighter. Each additional light adds more resistance, which results in less electricity flowing. To get them to blink faster, you'd need a shorter wire on the pendulum through the loop. A heavier weight would help them to continue blinking longer.
Magnets are more useful if you can turn them off and on.
The Basic Concepts
Moving electricity creates a magnetic field. If you make electricity run around and around in a coil of wire, you can concentrate the magnetic field and create a strong electromagnet. An electromagnet is much like a permanent one but with an added benefit: you can also turn it off and on at will.
Cut a 1-by-2 to be 3 inches long. With a 5/64-inch bit, drill two holes at each end of it. Cut two pieces of -inch dowel, about 4 inches and 2 inches. Hammer them in the two holes so that they stick out of opposite sides.
Drill a 15/64-inch hole near one end of a paint paddle.
With a nail bit, drill a small hole near the other end of the paddle. Drill a 19/64-inch hole near one end of a 6-inch 2-by-2.
Hammer a nail with a washer through the hole in the paint paddle into the 2-by-2 near the end without the hole. Don't hammer it in tightly — the paint paddle must be able to pivot around this nail easily.
Cut a piece of string a bit longer than the paint paddle.
Tie the string to the hole on the free end of the paint paddle. Slide the long dowel through the hole in the 2-by-2. With the paint paddle at about 90 degrees to the 2-by-2, tie the free end of the string around the dowel. This should be on the same side of the 2-by-2 as the nail with washer.
Drill a 15/64-inch hole in a film canister lid. Press it on the dowel so that the string is restricted to a small space between the lid and the 2-by-2.
On the table or floor, start a nail into the baseboard near one corner. Turn your 2-by-2 upside down and finish pounding the nail through the baseboard into the end of the 2-by-2.
Turn it over and the mechanical part of your crane is finished.
To build the electromagnet, cut about 6 feet of magnet wire. Sand off about 1 inch of insulation (lacquer) at both ends.
Wind the magnet wire around the bolt, leaving both ends sticking out a bit. Twist them to prevent unwinding.
Strip both ends of both thin wires and connect them tightly to the ends of the magnet wires. Keep the two points of connection from touching. This is the electromagnet.
Dangle the electromagnet from the tip of the paint paddle. Tape it on.
Run the wire down the paint paddle, then off to the side. Glue the film canister down to the base beside the 2-by-2. Fold some aluminum foil onto the end of one wire and stick it into the film canister. Put the battery in the film canister so that it rests on the wad of aluminum foil.
Place some paper clips or small nails on the table. Reel your crane down so that the electromagnet touches the pile of paper clips. To turn it on, connect the stripped end of the free wire to the top of the battery. When you see the paper clips sticking to the electromagnet, reel your crane up.
Pivot the 2-by-2 to swing the crane to the side. When the electromagnet is over the place you want to drop the paper clips, release the wire from the top of the battery and they should fall.
More to Think About and Try
* How is this project different from a real crane?
* How could you tell if a nail or bolt has become permanently magnetized?
* What do you think would happen if you hook up a car battery to the electromagnet you made?
* If you don't use wire with insulation, your electromagnet won't work. Why do you think that is?
A Little Background
Atoms of all elements have magnetic fields associated with them. These fields arise from quantum effects (having to do with electron orbits and spins — very difficult to explain) and are very small for most atoms. Iron atoms, and to a lesser degree cobalt and nickel atoms, have special structures that make a large magnetic field possible. These elements can become the permanent magnets you may find holding up a photo on a refrigerator door.
Electrons are subatomic particles that are less tightly bound to an individual atom than the more massive particles at the atom's center. Electrons may travel from one atom to another, and when they do, that movement is called an electric current. Every electric current creates a magnetic field. In this project you've made an electric current flow many times around a bolt. This "organizes" the magnetic field and results in two distinct poles at either end of the bolt. The bolt also increases the strength of the magnet; if you take it out, the electromagnet will be much weaker.
It is easy to increase the current to your crane, making the magnet stronger: just add more batteries. But if you hook your crane up to a car battery, which can provide enough current to turn an entire car engine, you'll rapidly have an extremely hot coil. The wire will likely melt down at its weakest point. (In addition, car batteries are dangerous. They are filled with acid strong enough to burn you and they sometimes produce hydrogen gas, which can make the battery explode and spray acid all over your face. If you want to increase the current, it is safer to use lantern batteries or line up several D cells than mess with a car battery.)
If your nail or bolt sticks to other iron objects after you switch off the electromagnet, you've transformed it into a permanent magnet. If you used wire with no insulation, when the electricity came to the coil, it would not need to go around and around along the wire. Instead, it could jump sideways from loop to loop until it came to the wire leading back to the battery. Electricity looks for the easiest path and will not go running around loops if there is a faster path — that is, a short circuit. Insulation keeps the current traveling down the wire so that it goes around the coil.
Electromagnets are generally used to move iron or steel objects. Some machines that sort recycled materials use magnets, and cranes such as this model use magnets to transport heavy iron or steel objects. But all materials are magnetic at a much lower level — that is, you can't often move them with magnets. The medical procedure known as magnetic resonance imaging (MRI) is performed by placing a person inside an enormous electromagnet, switching it on and off, and looking at the way the various atoms of the human body respond to the magnetic field.
A small motor and a small battery will make a small car go fast.
The Basic Concepts
The car in this project gets its energy from a battery. The motor will work only if it's connected in a complete circuit to the two sides of the battery. If you reverse the wires, the motor will go in the opposite direction.
Hot glue the tip of one craft stick to the center of another craft stick in the form of a T. Cut a drinking straw a little bit longer than the craft stick; then tape the straw to the craft stick as shown. It is best to make the straw stick out over both ends so that the wheels will rub on the straw and not the craft stick.
Make a hole in the center of three film canister lids with a small nail. Slide a bamboo skewer inside the drinking straw. Then put one wheel onto each end of the skewer. Cut the excess length, including the dangerous point, off the bamboo skewer.
Hot glue the motor to the end of the craft stick so that the shaft is exactly 90 degrees to the stick.
Press the last wheel onto the motor's shaft. If necessary, add glue to the end of the shaft to secure the film canister lid. Be careful not to let the glue cause the shaft to stick to the motor housing.
Strip the insulation off both ends of two wires. Connect the wires to the motor and wrap the excess wire around the craft stick.
Cut two pieces of aluminum foil and fold them several times into long rectangular shapes. Tape the pieces of aluminum foil tightly to the battery, leaving a bit of foil sticking up on each side.
Hot glue the battery to the top of the craft stick. Connect paper clips to the ends of both of the wires.
Connect the paper clips to the foil pieces sticking up off the battery. The car should go! Reverse the wires and watch what happens. If you want, make a flag from wire and paper and attach it to the back of the car as shown.
More to Think About and Try
* Where does the car get its energy?
* How can you make the car turn corners?
* How could you make the car go even faster?
* What can you do to make your car change directions?
A Little Background
Batteries store energy. There are two chemical reactions ready and waiting to happen in every battery. One of them creates excess electrons, and the other requires the addition of electrons. If you connect a battery's positive and negative terminals, the reactions begin happening and electrons go racing through the wire from the negative terminal to the positive one. This is electric current.
The wire you use to connect the terminals may get quite hot if you make a direct connection across your battery. The battery will also go dead quickly because all the chemicals are used up quickly in the reactions. To get some work out of the battery, you would need to send the current through something that will make use of the current, such as a motor.
Take apart a motor to see what is inside. You will find little coils of wire and little permanent magnets. When the motor has current running through it, those little coils turn into electromagnets. They then push and pull on the permanent magnets, making the motor turn. The electromagnets are turned off and on at just the right time by tiny brushes touching the shaft of the motor. When the electric current is going through the electromagnets in the opposite direction, they push and pull in the opposite direction and the motor turns in reverse.
By gluing either the front or back wheels at an angle, the car can be made to turn. If you had another motor to control the turn, you could make a remote-controlled car. If you want your motor to go faster, you could put on another battery, but that would also make it heavier. Heavier things generally have more friction, so it may not go faster after all. (Continues...)
Excerpted from Stomp Rockets, Catapults, and Kaleidoscopes by Curt Gabrielson. Copyright © 2008 City of Watsonville. Excerpted by permission of Chicago Review Press Incorporated.
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