Equatorial Ring

Model of Ptolemy's ring used to measure the length of the year.

What it shows:

This is a model of the ring and method used by Claudius Ptolemy (2nd century A.D., Alexandrian astronomer) to determine the length of a year.


How it works:

The ring is...

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Liquid Nitrogen Marshmallows

A big insulated bowl is filled with liquid nitrogen and marshmallows, which when frozen, are eaten in spectacular fashion.

Regular size marshmallows. Use wooden spoons, big bowl with holes for draining. Push down the marshmallows in the liquid nitrogen and mix to evenly freeze. Serve to volunteers. 

Eaten with open mouth and exhaling slightly gives the effect of dragon's breath.

Brownian Motion of Latex Spheres

“Under the microscope one, to some extent, immediately sees a part of thermal energy in the form of mechanical energy of the moving particles.” —A. Einstein 1915

What it Shows

Tiny latex spheres in water, viewed under a microscope, undergo a kind of random jiggling motion called Brownian motion—named after the botanist Robert Brown, who observed this kind of motion in 1827 when looking at tiny pollen grains. The spheres are all 1.054 micron in diameter. Each particle can be seen...

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Irregular Lamina

center of gravity - center of mass - equilibrium

What it shows:

The center of gravity fixed in (or outside) the object always orients itself with minimum potential energy on a vertical line below the support point. When an irregular shape is thrown into the air, it is seen to rotate about its marked center of gravity or center of mass (COM).

How it works:

We have several irregular lamina to suspend and/or throw in the air. They are (1) an amoeba shaped piece of masonite pegboard, (2) a cut-out map of the U.S. glued...

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Special Bouncing Collisions

Same as previous except that mass ratio of balls is 1:3 (softball:basketball) leaving basketball dead and softball four times the height.

tennis and basketball

Torsional Pendulum

Oscillation of mass on wire in torsional mode of oscillation.

torsion pendulum

What It Shows

The frequency of oscillation of a torsional pendulum is proportional to the square root of the torsional constant and inversely proportional to the square root of the rotational inertia.


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Doppler Tuning Forks

Run towards the blackboard carrying a tuning fork...

What it shows:

Waves emitted from a moving source are Doppler shifted to higher frequencies when moving towards the observer, and shifted to lower frequencies when moving away from the observer. In this situation the source is moving away from you, but the raised frequency sound is reflected back interfering and causing beating.

How it works:

All you need is a tuning fork (say 896Hz, see comments), a reflective surface like a blackboard, and plenty of room to take a run at...

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