Hot Road Mirage

What it shows:

There are various types of mirages possible, the details depending on whether the hot air is above or below the cool air and how sharp the transition is from cool to warm. This demonstration simulates what happens when a dark asphalt road gets much hotter than the air around it--the air next to it becomes hotter than the higher air and light traveling through this temperature gradient is bent so much that it appears reflected. The shimmering water on a road's surface or the blue oasis in the desert are natural examples of blue skylight being...

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Photoelectric Effect

What it shows:

A direct observation that the photoelectric effect is color (i.e. frequency) dependent and not intensity dependent. We discharge an electroscope using UV radiation after all attempts to discharge it with light of a longer wavelength has failed.

How it works:

An ebonite rod and fur is used to place a negative charge onto a Braun electroscope (figure 1) fitted with a thick zinc plate. Deviation of the electroscope arm from the vertical indicates a net negative charge. Next we hit it with light from a 1000W...

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Potential Well Orbiter

Orbital motion simulated by ball rolling on wooden potential well.

What it shows:

Motion in a central potential is demonstrated by a ball rolling on a circular 1/r curved surface.

How it works:

The 1/r potential well simulates the gravitational potential surrounding a point mass; a ball bearing moving in this potential follows a parabolic or elliptical orbit depending upon its initial trajectory and velocity. As it loses energy due to friction, the orbit decays and the ball spirals towards the centre of the well. You could...

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Nuclear Fission

What it shows:

In a nuclear reactor or atom bomb, a fissile material such as 235U can capture a neutron. The resulting unstable nucleus fragments into two smaller nuclei, releasing energy and several neutrons (a typical equation is given below). Each of these neutrons can in turn cause the fission of a 235U nucleus. If there is above a critical concentration of fissile material, this chain reaction will continue unaided, and if unregulated can result in a very loud bang.

n + 235U → 236U* → 141Ba + 92Kr + 3n

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Giant Vibrating Crystal

What it shows:

A simplified model crystal with non-rigid inter-atomic bonds. You can show that solids really do vibrate, distort and expand.

How it works:

A cubic lattice of 3×3×3 15cm diameter Styrofoam™ spheres linked by 3cm steel springs. The springs are epoxied to corks embedded in the Styrofoam.


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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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Weighing Moles

Several samples are weighed on the balance; each is a mole.

The electronic scales are set up in front of the video camera. In a secondary container on the scale platform is a cube of lead weighing 208 g., 18 g of water in a bottle with an empty bottle for tare, and 200.6 g of mercury in a bottle with an empty bottle for tare.

Specific Heats of Oil and Water

A volunteer puts her hands in oil and water in large beakers on thermostated hot plates, at about 60°C. The water beaker hand is removed almost instantly. The oil beaker hand can remain indefinitely.

The heat capacity of oil is about half that of water. Oil is thought of as hotter because it can be heated to higher temperatures than boiling water, but at the same temperature, water moves more heat into your hand than oil does.