[★★★]

Balancing Forks

Two forks, a cork, and a matchstick balance on the lip of a glass.

What it shows:

Balancing two forks in an unlikely configuration is a lesson in finding the center of mass and stable equilibrium. Nothing too deep here, but it's fun.

balancing forks

How it...

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Egg Shell Strength

What it shows:

Eggs have a reputation for being quite strong under compressional loads. You won't believe your eyes when you see how strong they actually are — an egg can support a person!

How it works:

An egg shell is a composite material, but primarily calcium carbonate, "nature's ceramic."1 We assume the ultimate compressional strength of the material to be about the same as bone (which is mostly calcium phosphate, but never mind): 170x106 N/m2. The diameter of a "large" chicken egg is about 1.75" and the typical shell...

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Standing Wave in Metal Rod

An aluminum rod, supported in the middle, rings for a long time in its longitudinal mode.

What it shows:

Longitudinal standing waves in solids.

How it works:

A metal rod is not unlike an organ pipe with both ends open. Holding it exactly in the middle will force the simplest, or fundamental, mode of vibration -- the ends will be free to vibrate maximally and the center will be a node. The fundamental frequency happens to be 2.26 kHz. As with a pipe open at both ends , the rod will vibrate at all the odd as well as even...

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Giant Capacitor

What it shows:

The basic principles of the parallel plate capacitor made large.

How it works:

The capacitance C of a simple parallel plate capacitor is given by


the ratio of the magnitude of the charge Q on either conductor to the potential difference between the...

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Para and Diamagnetism

What it shows: 

The behavior of a substance in a non-uniform magnetic field will depend upon whether it is ferromagnetic, paramagnetic or diamagnetic. Here we test different substances to see how they are influenced by a magnetic field.

How it works: 

We have a collection of samples (listed in table 1) that exhibit well the three magnetic properties. Diamagnetic substances have a negative relative permeability (susceptibility); paramagnetic substances have positive.

Ferromagnetic substances have...

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Bouncing Light Beam

What it shows:

As a simulation of atmospheric refraction, this demonstration shows the gradual and continuous bending of light due to a gradient in the optical density of the medium. In this case the variable refracting medium is a tank of sugar water with a vertical gradient in the concentration of sugar and a HeNe laser provides the light beam. It can be used as a model of mirage formation (except that the direction of increasing refractive index is in the opposite direction) or even as a representation of the refraction of seismic waves through the Earth's...

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Collisional Broadening

What it shows:

Perturbation by colliding atoms in a high pressure gas result in the broadening of emission and absorption lines. This is clearly seen in the sodium D (589nm and 589.6nm) lines of a high pressure sodium lamp.

The broadening in frequency width is dependent upon the separation of the perturbing particles (Novotny 1973) by

∆ν ∝ r-n

With n=2 the broadening is due to the coulomb field of an ionized atom or electron; this is the linear Stark effect. With n=3 the interaction is between neutral atoms of the same type; this...

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Mixing and Unmixing

Food coloring in glycerine is mixed by turning a drum, then unmixed by reversing. Has entropy decreased?

What it shows:

Ink is squirted into a fluid and mixed in until it disappears. By precisely undoing the motions in the reverse direction, the ink becomes unmixed! The demonstration seems to defy thermodynamics in that it appears that entropy decreases, but in actuality the reversible mixing is made possible by insuring that the mixing/unmixing is done without turbulence.

How it works:

The space between two, transparent and concentric...

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Coriolis Effect

As demonstrated by two people throwing a volleyball to each other while sitting on rotating platform.

What it shows: 

The Coriolis force is a pseudo force existing in a frame that rotates with constant angular velocity to a reference frame. It acts on a body moving in the rotating frame to deflect its motion sideways. Here the audience sits in the reference frame, while two volunteers on a rotating platform experience the coriolis force by trying to basket a volleyball.

...

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