Astrojax is a fascinating new toy illustrating a wide variety of basic science principles.

PLANETARY/ORBITAL MOTION
During vertical orbits the outer ball orbits around the middle ball. However, just as with the orbital motion of the earth and moon, neither ball is still - both balls are in motion. During horizontal orbits, both balls orbit in perfect circles. Our earth orbits around the sun and our moon orbits around the earth in ellipses which are not quite circular, but close!

ROTATIONAL DYNAMICS
A metal weight concentrates the mass at the center of the middle ball. This allows the middle ball to spin rapidly. (A diver uses the same principle when she tucks into a ball during a dive so she can spin faster. Similarly, an ice skater uses this principle when he brings in his arms during a twirl to spin faster.) Because the middle ball can spin rapidly, the string never tangles around the middle ball!

FRICTION
During horizontal orbits the middle ball does not slide on the string, so energy is not lost to friction. This is why horizontal orbits last a long time without any hand motion. However, during vertical orbits the center ball does slide up and down on the string. (If you listen closely you can hear it sliding.) Therefore energy is lost to friction, and vertical orbits require tugs of the hand to add energy to sustain the orbits.

CENTRIPETAL FORCE
As the velocity of the horizontal orbits increases, the string attached to the end ball becomes more and more horizontal. As the string becomes more horizontal, it can exert more inwards force on the end ball. This illustrates that the inward force required to produce circular orbits increases as the velocity of the orbits increases.