Fraunhofer Absorption

What it shows:

Sodium 'D' line absorption showing up as a black line in the yellow of a continuous spectrum. Good as a simulation of the sodium portion of the Fraunhoffer absorption spectrum caused by atoms in the solar atmosphere; it does not however, resolve the 5890/5896Å doublet.

How it works:

As in the Sun, which is a black body source surrounded by an atmosphere of cooler gas containing many heavy atoms including sodium, we can set up a black body spectrum using a slide projector, and provide a hot sodium 'atmosphere' using...

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The microcystaline structure of a steel wire changes from body-centered-cubic to face-centered-cubic as it is heated to red-hot.

What it shows:

Iron atoms are arranged in a body-centered cubic pattern (BCC) up to 1180 K. Above this temperature it makes a phase transition to a face-centered cubic lattice (FCC). The transition from BCC to FCC results in an 8 to 9% increase in density, causing the iron sample to shrink in size as it is heated above the transition temperature.

How it works:

A three meter length of iron...

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Local Group of Galaxies

Lights-up-in-the-dark three-dimensional model of the local group.

What it shows:

Three dimensional model of the local group of galaxies, with a scale of 1mm = 1kpc.

How it works:

A large wooden base board forms an x-y plane from which the approximate relative positions of the local galaxies are measured. The galaxies are LEDs and (for the two biggest, the Milky Way and Andromeda) 6V bulbs, mounted atop 8mm diameter plastic tubing; the length of the tube gives a z-axis position of the galaxy. The wires from the LEDs and...

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Feather and Dime

Falling in an evacuated tube at the same rate.

What it shows:

In the absence of air resistance all bodies, regardless of size or weight, fall with the same acceleration at the same point above the Earth. Here a feather and a dime (see Comments) fall under the influence of gravity in an environment where there is no air to mess things up.


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Barrel of Fun

What it shows:

An object finds itself heavier and pinned against the wall of a spinning cylinder; the principle behind fairground Barrel of Fun rides and centrifuges.

How it works:

The object in such a ride experiences two forces, that of its weight and the centripetal force exerted by the barrel wall; the vector addition of these forces giving the apparent increase in weight (figure 1 ) The reaction force of the object also presses it against the wall; the increased friction force preventing it from sliding down.

The barrel in our demo is a 45cm...

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Driven Damped Oscillator

Single air track glider, with and without variable frequency driver, variable damping, and oscilloscope position vs. time display.

What It Shows

With one end of the car attached via a spring to the end of the track and the other end of the car coupled (via a similar spring) to a driving motor, we can see how the car behaves when it is driven below, at, and above the resonance frequency. Markings on the motor help to show the phase relationships between the driver and car at different frequencies. A storage scope tracks the motion of the car (see Setting It Up...

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Semimusical Blocks of Wood

What it shows:

Drop a piece of wood on the floor and listen to the sound it makes. It may sound like noise, but it also makes a "semimusical" sound which is so poor in quality that one would be hard pressed to call it musical. Yet it is not pure noise because the sound contains a series of regular impulses that have a pitch. This may be demonstrated by dropping wood bars (one by one) onto the floor — a musical scale or tune is easily recognized.

How it works:

The tuned wood (oak) bars are 6½" long and 1" wide with thicknesses...

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TV Image Deflection

Image on black and white television is deflected by a magnet, not unlike the Maltese Cross.

What it shows:
The television is basically a sophisticated cathode ray tube. The electron beam in the TV is influenced by magnetic fields in the same way as in Crookes tubes.

How it works:
The image on a black & white TV is formed by a single electron gun scanning the screen. Holding a strong magnet to the side or in front of the screen deflects the beam from its regular sweep pattern, distorting the image.


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Driven RLC Circuit

rlc circuit

What It Shows

The amplitudes and relative phases of the voltages across the individual elements of a series RLC circuit varies with the frequency of the driving voltage. The voltages of the three elements plus the driver are plotted simultaneously on an...

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