Top Secret

This toy teaches electromagnetism and torque. The Top Secret is manufactured by Andrews Manufacturing Co. at 2121 Franklin Blvd. Eugene OR. 97403. Tel: 1-800-238-2892. This top seems to be running by perpetual motion.  The little spinning top just spins and moves randomly on a slightly concave dish forever!  As a scientist you know that this is impossible without an external supply of energy.  Energy has to be conserved and also there must be a torque on the spinning top to compensate for the friction.  So how does it work? 

The Secret:  There are several essential components of this toy that make the top spin and move around.  They are a coil of many turns of wire, a transistor and a battery, all hidden underneath the dish, as shown in the picture. In addition, there is the top itself, which you will find is magnetized parallel to a diameter.

As the top spins the coil senses a change of magnetic field.  According to Faraday's law, a changing magnetic field flux induces a voltage in the coil. This induced voltage turns on the transistor, which acts as a switch between the coil and the battery.  When the transistor is turned on the battery provides current to the coil which in turn produces a magnetic field at the spinning top.  This magnetic field coupled with the top's magnet forms a torque to overcome the friction and to continue and to increase the spinning of the top. The transistor is turned on and off for a very short time, depending on when the top has rotated its magnetic field past the center of the coil, the polarity of the induced voltage and the time constant of the coil circuitry.  Once the transistor is turned off, it cuts off the current in the coil, terminating the magnetic field in the coil.  The top spins freely without the interaction of magnetic field until it rotates into the coil again.  The whole process repeats.

If the top is not moving then the transistor does not get the induced voltage so it will turn itself off.  In which case the battery is also turned off.  This is why the battery will last a long time. 

As to the details how the spinning continues to be in the same direction and the details of how long the transistor is turned on and off and the coupling of the energy pumped into the coil, it is very complicated and is in the design of the Top Secret!