Ghost Eyeballs | Growing Spheres

Norman Barstowby: Norman Barstow

Educational Innovations’ Growing Spheres can be used to add a note of ‘horror’ to your classroom or home Halloween experience.  Once fully expanded, Growing Spheres have an index of refraction almost identical to that of water. This means that when the Growing Spheres are placed in water, they are nearly invisible.

Growing SpheresMaterials:

  • A large (2 qt or larger) translucent plastic storage container and lid.
  • Growing Spheres : GB-730 (these are the size used for the photos)
  • Water
  • Label for the container lid: GHOST EYEBALLS Read the rest of this entry »

Make Your Own Clock Faces

Martin Sagendorfby: Martin Sagendorf

A Definition:

Clocks measure time – it can be a continuous measure of events passing or the measure of the interval between two events.

Of Hours:

After years of evolution, our modern clocks now divide the day into 24 equal length hours.  And, as we know, there are two systems in use today: Americans use the “double-twelve” system while the rest of the world uses the 24 hour system.

As An Aside:

The word “hour’ comes from the Latin and Greek words meaning season, or time of day.  A “minute” from the medieval Latin pars minuta prima (first minute or small part), originally described the one-sixtieth of a unit in the Babylonian system of sexagesimal fractions.  And “second” from partes minutae secundae, was a further subdivision on the base of sixty – i.e. “a second minute”.  (ref. Pg. 42 The Discoverers by Daniel J. Boorstin)

The “Double-Twelve” Clock Face:

Has 12 at the top – probably because at noon the sun is at its highest point in the sky.


We can make a clock with 12 o’clock anywhere we wish and the clock will still work just fine. Read the rest of this entry »

The Bottle Balancer

Ron Perkins

by:  Ron Perkins

The bottle balancer is a fascinating conversation piece that illustrates the principle of center of gravity!  A small hole in an oak board allows you to balance a 2-liter soda bottle at an angle that appears to defy gravity. This can be used as a teaching tool or a centerpiece at your next party!  Hold the special angle cut of the wooden, bottle balancer board against a flat horizontal surface.   When a full, sealed, 2-Liter soda bottle is inserted into the wooden hole from above, it will catch the bottle flange and the wood/bottle assembly balances at a surprising angle.

Bottle Balancer

Explanation of Bottle Balancer:

In order for an object at rest to NOT tip over, its center of gravity, or its center of mass must be directly over its base. A goose-necked desk lamp is usually quite stable, unless it is configured so that the lamp part is stretched horizontally, far from the large base.  Then, it becomes less stable and often tips over.   The wood/bottle assembly example is more complicated than the lamp example because if the bottle is moved, the flowing liquid results in a change of its center of mass. Read the rest of this entry »