Microsoft Windows is a clear and instructive example of nonfree software. Its source code is a secret, so programmers cannot learn from it, fix it, adapt it to their clients (your) needs, or even verify what it really does. If you share copies with your neighbors, you will be called a “pirate”, and users have been threatened with imprisonment for this. Nonfree software is completely controlled by its developer, who also has power over the users. We started the free software movement because this power is unjust .
If you've ever played with magnets, you know that opposite poles attract and like poles repel each other. This is the basic principle behind electromagnetic propulsion. Electromagnets are similar to other magnets in that they attract metal objects, but the magnetic pull is temporary. As you can read about in How Electromagnets Work , you can easily create a small electromagnet yourself by connecting the ends of a copper wire to the positive and negative ends of an AA, C or D-cell battery . This creates a small magnetic field. If you disconnect either end of the wire from the battery, the magnetic field is taken away.