This great little lab stirrer (which I modified to have a transparent top) can be used in many investigations and demonstrations:
From Amazon: BUY NOW Magnetic Stirrer
Inexpensive concave lenses make great spinning platforms- get one here:
From Amazon: BUY NOW Concave Lens Spin Station
Induced Current Spin-Up: Spinning magnets from the magnetic stirrer induce electric currents to flow in the brass PhiTOP- these currents then create their own magnetic field which opposes the magnets underneath and pushes the PhiTOP to spin. Credit to astrophysicist Kenneth Brecher, the creator of the PhiTOP and this unique means of using Lenz’s Law to spin it up. This top stands up vertically (when spun with sufficient rotational velocity) due to physics similar to that of the tippe-top. The concave lens keeps the top from wandering off of magnetic stirrer.