Electromagnetic Launcher Student Materials

STUDENT

WHY DOES THIS PROBLEM MATTER?

Did you know that railroad locomotives actually have electric motors to turn the wheels and diesel generators to power the motors? Motors, generators and other electromagnetic things operate with the same principles at work in a simple solenoid, a coil of wire that looks like a spring and has electric current passing through it. This project will let you explore electromagnets, the basis for motors, generators and solenoids, and discover how such a simple device can be used in some fun and creative ways.

WHAT ARE WE SUPPOSED TO DO?

The design problem is to use some simple materials like wire, straws, paper clips, and nails along with the power in a couple of batteries to launch a simple metallic object (all or some portion of a nail or paper clip) at targets.

Your design team should discuss the different possible components of the launcher (coils, the projectile, most importantly the switch, etc.) before any construction is started. Your design team must decide what the overall configuration of the launcher will be and how it will be constructed. Your team should also spend some time exploring each others ideas and testing prototypes. After your team has thought about the problem for a while and decided on a plan of action, involve everyone in the construction. When your team winds the wire on your launcher, make sure one member keeps the wire from tangling.

Project Constraints

Your teams launcher must conform to several constraints. First the location of the nail can start no higher than 5in above the flat surface that the launcher and targets rest on. Second, the whole device must fit within a 7in x 7in x 7in volume.

WHAT EQUIPMENT AND MATERIALS CAN WE USE?

You will only need some very basic hand tools for this project. Scissors, sheet metal cutters, and wire cutters will be available. You may use any of following materials in your launcher.

Materials

• One Soup Can

• Two Coffee Stirring Straws

• Two 9 volt Batteries

• Fifty Feet of Copper Wire(30gauge)

• Two Drinking Straws

• Three Paper Clips

• One cardboard Cereal Box

• One Strip of Tacky Stick

• One Large Nail

• One Small Nail

• One 12 in piece of Tape

Figure 1. Magnetic field around conducting wire. Field is strongest very close to the wire.

WHAT MIGHT BE USEFUL TO KNOW?

Electromagnetic things operate by making magnetic fields with wire that is conducting electricity. Magnetic fields are invisible, but can be felt if two solid magnets are held close together but not allowed to touch. You will feel either attraction or repulsion. The magnetic field that is induced around a single, current carrying wire is shown in Figure 1.

When a single strand of wire is connected to a battery, a current flows through the wire, and at the same time a magnetic field is produced right around it. Figure 3 shows what would happen if that single strand of conducting wire was placed close to a magnet.

A nail with wire wrapped around it can be magnetized, or made into an electromagnet by connecting the wire to a battery. The wire of an electromagnet is often wrapped around many times to intensify the magnetic field. The more wire that is wrapped around the nail, the stronger the electromagnet will be (Fig 2). So, the electromagnet is actually a circuit with a voltage source and a coil of conducting wire.

Figure 2. As you increase the number of windings, you increase the strength of the electromagnet.

Electric Current and Voltage in Circuits

Electric devices are described in terms of the voltage and current necessary in their operation. A circuit is a complete loop of conducting material. A flashlight circuit on up to the complex circuits in a computer may be described in terms of their voltage and current. Electric current is actually the flow of electric charges around the circuit. When the circuit is cut or opened the current will stop flowing. Voltage is just like the force of water pressure pushing water through pipes, only it is pushing charge through conductors. Batteries in a flashlight push charge around the circuit whose main component is the bulb. The bulb acts as a resistance to the current and heats up until the small wire glows brightly. Your design may also include batteries to push current through a circuit and the most important component may be a solenoid.

Figure 3. When a piece of copper wire is placed close to a magnet, there appears to be no magnetic interaction (A). But when a current is allowed to flow in the wire, the magnetic field induced around the wire interacts with the magnetic field of the magnet and causes it to be pushed away from (B) or attracted toward (C) the magnet.

Solenoids and their Magnetic Field

A simple solenoid, and the magnetic field produced when an electrical current flows through the conductor coils is shown in figure 4. If an iron containing material was placed inside the coil of figure 4, a magnetic field would be induced in it and it would act just like a common magnet with north and south poles. You could use a nail with a current carrying wire wrapped around it just as you would use any solid magnet.

Figure 4. Simple solenoid showing the electric current, magnetic field right around wire, and the direction and orientation of the magnetic field produced by the combined conducting coils.

Figure 5. Cut away view of a typical solenoid with a voltage source and switch (A). When an iron containing material is placed near one end, a magnetic field is set up in it. The interactions of N and S poles of the material with those of the nearby coils cause an acceleration of the material (B). As the material moves toward the center, the effect of the opposite poles equalizes (C). If the circuit is opened quickly, the momentum of the material will carry it out the other end (D). Because the current carrying coils will set up a magnetic field in any iron containing material that is placed inside or near them, you can use the opposite poles that are produced to move the material (Fig. 5). The maximum attraction occurs when the iron cylinder is half way into the coil. Solenoids are used in practice for tripping safety mechanisms, operating regulating devices, opening and closing valves, and many other applications.

Aiming Projectiles

By changing the angle that the projectile is launched at you can directly affect how far it goes (Fig 6). If the launching angle is very small the nail will hit the surface quickly and probably travel farther away after bouncing, whereas if the angle is large the nail will reach a higher point before hitting the surface but will come to rest close to the launcher.

Figure 6. The horizontal distance that the launched projectile travels is related to the launch angle.

HOW WILL WE KNOW HOW WELL WE HAVE SUCCEEDED?

When the launcher is tested, the only action that will be allowed by your team is any action that directly involves closing an electric circuit. With this action, the launcher must begin its performance which will be considered over when the launched projectile comes to rest. Your team will have five chances to demonstrate the performance of your launcher. Your team will be allowed thirty seconds, if you need it, to reset the launcher before each attempt.

Basic Performance Index

Good performance will be demonstrated by any launcher that launches the projectile.

Extra Performance Index

Better performances will require that the projectile travel at least one foot and the EPI may be evaluated by:

SAFETY CONSIDERATIONS

If you were to take a small piece of wire, say 3 in long, and hold it to both ends of a nine volt battery, the wire would heat up quickly. If the wire is very thin, like the wire you will be using during the project, it may heat up enough to cause a burn. Be very careful with the circuits you design and test to assure that there is enough wire windings in the circuit so that it will not heat up enough to burn someone or cause a malfunction with the device. Also, be sure that when you test the final launcher or launcher prototypes there is no one in the direction of the nails path. A good practice would be to make sure everyone is behind a vertical plane that is perpendicular to the nail's path during launching. Finally, if you decide to cut out pieces from the soup can, be very careful with the sharp edges.