Mechanical energy is produced when an energy source is expended to create the physical motion of an object. In the case of a human being, the body burns nutrients from food which is then used to perform work like pedaling a bicycle. In this case, nutrients are converted into physical, mechanical force to propel the bicycle. The mechanical energy can then be converted to electrical energy through a generator where magnets and coils turn motion into voltage and current.
Mount a car alternator onto the piece of plywood so the alternator sits upright. Use bolts to attach the alternator into place, then set the flat surface of the plywood into the corner of a wall to prevent the unit from sliding.
Fill the indented groove of the alternator pulley with black electrical tape and be sure to cover both sides of the pulley's grooves so the sharp edges are not exposed. The entire pulley should resemble a rubber wheel once the tape has been applied generously.
Position the bicycle so the rear tire is resting on the taped pulley and then raise the back wheel of the bicycle off the ground, holding it up by placing one or two railroad ties under the bicycle frame. Be sure the wheel is pressing against the pulley with as much pressure as possible.
Connect the alternator's wire harness to the alternator's plug. Strip 1 inch of insulation off of the two wires coming out of the harness. There should be one black and one red wire. The black connects to the negative post of the automotive battery and the red connects to the positive post.
Install battery terminals on the stripped wire ends, securing the terminals onto the wires with an appropriately-sized screwdriver or wrench, depending on the type of terminal obtained. Connect the terminal of the black wire to the negative post of the automotive battery, then connect the red wire to the positive post of the battery. Tighten to secure them into place.
Sit down on the bicycle and begin to slowly pedal the bike. Watch as the rear wheel of the bike begins to turn the taped pulley on the alternator. Pedal as fast as possible for about 15 to 30 minutes, making sure the bicycle doesn't tip over while resting on the railroad ties. Balance the bike just as you would if riding. The alternator will be converting the mechanical energy of the bicycle wheel into electrical energy which is stored in the battery.
Remove the terminals from the battery and connect any 12-volt DC device to the battery posts and note that the battery has enough of a charge to run the device for 1 to 5 hours, depending on the amount of power the device pulls from the battery to operate. When the battery is depleted, recharge with the bicycle and alternator system.
A more permanent bicycle-powered electricity generation system may be designed with some machining work done to the rear of a bicycle, and to the pulley of an alternator. The pulley on the alternator can be replaced with a bicycle sprocket, to which a chain connects between the front sprocket of the bicycle and the sprocket on the alternator, with the rear wheel removed. A more stable and permanent bicycle mounting rack can also be made, making operation much simpler.
A generator of some sort, consisting of internal coils and magnets, is always used to convert mechanical energy into electrical energy. The rotation of the magnets is performed by chain or belt interconnection between the source of mechanical motion, such as pedaled bike, car engine or water turbine, and the driven generator or alternator.
Electricity stored in the battery, no matter how it was produced, is very real. Never short the posts of the battery together which can cause sparks and possible electric shock.