MadSci Network: Engineering |
An electro-magnet is a type of magnet that can be switched on and off. This is formed by winding a coil of wire around a piece of magnetic steel. When you apply a voltage to the wire, the wire forms a magnetic field. A switch can be used to connect the voltage to the wire. If you wind wire around a nail and put a voltage through it, you can pick up small washers and other pieces of steel just like with a regular permanent magnet. Unfortunately, the drag strip you describe is not so simple to use this effect. Magnets can attract a magnetic car which has some steel in it, but it is very difficult to attract steel with a magnet for a very long distance such as the 3 feet you describe. So unless you can pull the magnet down the track ahead of the car, your car won't go very far. If the car contains a magnet itself, you could use the opposite polarity of the magnet to push the car down the track by repulsion of like poles. But even this only works for short distances, probably only a fraction of an inch or so. To really get your car up to speed so that it reaches the end, you have to know a little bit more about the physics of the problem. To accelerate an object like a toy car which weighs M lb up to a speed, V, you have to push it with a force,F for a time, T. The car will accelerate with an acceleration of A = F/M For every second you apply the force, the speed will increase by A*T or F*T/M But as soon as you stop pushing on the car, it will travel at the final speed until friction of the tires, etc slows it down. Since you will be able to repel the car by your electromagnet for a short distance, as soon as the car leaves the field of the magnet, it will begin to slow down. If you want to make your car go fast, you have to have a really powerful magnet that will kick the car with a large force so that it gets up to speed very quickly before it leaves the magnet. This is just like having a large spring that would kick the car just like a pinball plunger kicks a pinball in a pinball machine. Such a magnet will require probably more than a small battery to power it. In fact, a magnet such as this will want to draw a lot of current which will run the battery down with only a few tries. To make the force last along the length of the track, you would need to build a linear motor which is used to power some monorails. This is rather complicated to do. You might try looking up electromagnet in a science encyclopedia and see how you might build one to try pushing your car. You may need more than a battery to power it, however, so get an adult to supervise the construction and use. I found the following website which shows the complicated formulas used to determine the strength of a magnetic field of an electromagnet. I couldn't find much else in the way of web sites that explain their construction. http://www.geocities.com/CapeCanaveral/Hall/6153/
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