Thoron Decay

What it shows:

The very first determination of a half-life for a radioactive decay was made by Rutherford. 1 In a study of the properties of thorium emanation, he found that the intensity of the radiations fell off with time in a geometric progression. That historically important result is reproduced in this demonstration experiment. The gas thoron, or thorium emanation, is an isotope of radon (86Rn220) which decays by α emission and has a half life of 55.6 seconds. 2 Using an emanation electroscope, we observe the...

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Convection Cell

What it shows:

Hot fluid rises, cool fluid sinks. Here is a desktop convection cell modeling the processes in the atmosphere, oceans or stellar interiors.

How it works:

The currents are set up in rheoscopic fluid 1 (basically minute aluminum flakes in water) in a small 10×10×15cm glass tank. Half the base of the tank rests on a heater, the other on an aluminum block that acts as a heat sink. The rheoscopic fluid has a weird metallic sheen such that the bulk motion of fluid is clearly seen from the changing reflectivity....

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Kepler's Universe

Model of the solar system based on the five perfect solids.

What it shows:

Kepler attempted to describe the orbits of the planets in terms of the five regular polyhedrons. The polyhedrons, inscribed within one another define the distances of the planets from the Sun. They act as (invisible) supporting structures for the spheres on which the planets move. The order of the solids outwards from the Sun are the octahedron, icosahedron, dodecahedron, tetrahedron, and hexahedron.

How it works:

A contemporary illustration of...

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Cooking Ice vs. Cooking Eggs

An egg size piece of clear ice is dropped into a hot frying pan, with hissing and melting and steaming from solid to liquid to gas . An egg is carefully dropped into another hot frying pan, and it transforms from liquid to solid.

A small water bottle in the freezer overnight will freeze solid.  Cutting off the plastic and breaking the ice with a hammer will generate the egg size piece of ice.

Vector Sum of Forces

Magnetic blackboard mechanics with spring balances and weights.

What it shows:

Solve a problem in composition of concurrent forces by graphical or trigonometric means.

How it works:

The blackboard mechanics set1 includes apparatus to demonstrate most of the common laws of statics and some dynamics. The pieces of apparatus are held on the blackboard by magnets and, although not large, are fairly visible in the lecture hall. A booklet with a few dozen suggested demonstration experiments is included in the set.

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Ball on string orbits with increasing speed as string is shortened.

What it shows:

An object moving in a circular orbit of radius r has an angular momentum given by:

L = r × mv = mr2ω.

A simple way to show conservation of angular momentum is a ball on a string, whirled around your head. As you change the length of the string, the ball's orbital speed changes to conserve angular momentum.

How it works:

The orbiter consists of a meter length of cord with a wooden ball at one end and a wooden anchor at the other. The cord passes...

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Fracture Strength of Chalk

What it shows:

This demonstration allows you to compare chalk’s compressive strength with its tensile strength.

How it works:

We use railroad chalk, which although being softer and harder to work, is nice and big and easy to see. A sample is placed in each of the two types of testing assembly (details in Setting it Up), and loads carefully applied. Railroad chalk has a tensile strength of 195kNm-2 ± 30kNm-2 (a load of 2.5 to 3.5kg) and a compressive strength of 500kNm-2 ± 65kNm-2 ( a load of 7 to 9kg).


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What it shows:

The effect of length, tension, diameter, and kind of material on the pitch of a vibrating string is demonstrated. One may also show the harmonics of a vibrating string.

How it works:

The sonometer is a long hollow wooden box along the top of which are stretched one or more strings rigidly attached to the box at one end, with provision at the other for changing their tension. If there is just one string, it's known as a monochord. The monochord illustration is from John Tyndall's book entitled Sound, (...

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