Magnetism
You know that a magnet can attract some objects, but not others. For instance, a magnet will attract a paper clip, which is made of metal, but not an apple. That is not all. If you try to attract an object made of copper or aluminum with a magnet, it will not work. What this tells you is that there must be a property that some materials have that makes them feel the attraction of a magnet. An apple, a US penny (which is made of copper), or a piece of aluminum do not have this property and they do not feel the attraction of a magnet. On the other hand, a paper clip does. Something else you may want to think about is that the shape of an object does not appear to change this property: if you cut the apple into slices, still it is not attracted by the magnet; and if you uncoil the paper clip, it still is attracted. So, shape does not account for this difference.

Charged Objects
A similar concept holds in the case of electricity. You know there exists a property of objects, called charge. Charge can only be positive, negative, or zero. If an object has a positive charge, you can say it is positively charged. If it has a negative charge, you can say it is negatively charged. If an object has no charge, you can say it is uncharged, or neutral. You have learned that, if two objects have like charge (both positive or both negative), they repel. On the contrary, if they have opposite charge, they attract. You may have been told that if both objects are neutral, they are indifferent to one another - they neither attract nor repel.

Neutral Objects
The idea that neutral objects neither attract nor repel one another seems to make a lot of sense. Most of the time, you are neutral and the walls of your house are neutral, too. And, in fact, you do not feel attracted by the walls of your house! However, as most things you learn in physics, this concept is only valid to a point. It is important for you to understand that, in fact, neutral objects do act on one another when they are very close. This is very important in practice in a new field of technology where everything is extremely small. This field is called microtechnology.

Micro!
The word ``micro'' refers to the fact that, in this type of technology, things are as small as one-millionth of a meter, or even smaller. When you studied the decimal system, you have seen the length of a meter. You have also seen that, if you divide a meter into one thousand parts, you get millimeters. A millimeter is quite small, but you can still see it. Now imagine dividing that one millimeter into a thousand parts again! What you get is called a micrometer. You cannot see a micrometer on your meter stick - it's just too small. You know that the diameter of a circle is its size measured by a segment going across its center. Well, the diameter of any human hair is approximately 100 micrometers. Imagine a small machine made of parts the size of a small fraction of a human hair. Building such small machines is what microtechnology is all about.

Microtechnology
Since in microtechnology every part is so very small, everything is also very close. For instance, in some micromachines engineers build something that looks like a microbridge crossing over a microgap below (can you understand the meaning of all the words that begin by the word micro- in this sentence?). Well, if the microbridge is built too low over the material below, it may be attracted by it so strongly that it sticks to it! And yet, both the bridge and the material below are completely neutral! Therefore, engineers must be careful to not build micromachines with parts that are so close that they may stick together. These forces that cause small parts to stick together are called surface forces, because they act between the surfaces of each object. For instance, the lower surface of the bridge and the upper surface of the material below attract one another.

Electric Machines
Well, you know about electricity and about magnetism. You also know that electricity and magnetism are used in very many appliances and machines that you use in every day life. Electric motors, computers, lights, television sets, telephones - all these have been made possible by understanding and exploiting electricity and magnetism. That is, when you understand a force, you can exploit that force to make a machine out of it, or an appliance that will do some type of work for you.

Micro Machines
Nowadays, scientists and engineers are trying to see whether it is possible to make new machines and new appliances that will use surface forces instead of electricity and magnetism. Since surface forces are very strong when the machine parts are small and so very close, it surely makes sense to try and see if we can use this to our advantage.