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BCC to FCC

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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Change of Volume with State

CO2 and He balloons in liquid nitrogen.

What it shows:

Cooling a gas causes a proportional decrease in volume with the drop in absolute temperature. A gas such as helium, which remains close to ideal at low temperatures, shows a four-fold decrease in volume when taken from room temperature 330K to liquid nitrogen temperature, 77K. Carbon dioxide however, sublimes at 194.5K, so is solid at 77K. Oxygen liquefies at 90K (S.T.P.). A qualitative demonstration of these effects can be shown with gas filled balloons.

How it works:...

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Cloud in a Bottle

A 5-gallon bottle containing air and water vapor is slightly pressurized; a sudden release of the pressure cools the vapor, forming a cloud.

The bottle is a heavy Pyrex carboy with tooled mouth. A one-holed rubber stopper fits the mouth and is air-tight. A meter of Tygon tubing is fitted to a short tube in the rubber stopper.

The bottle is kept stopped and wet, and should work off the shelf. If the bottle is dry, spray about 10 ml of distillled water inside.

To demonstrate cloud formation, fit the stopper to the bottle and apply pressure with the lungs. Blow into the...

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Dippy Duck

Evaporation of water on duck's head cools vapor inside causing low pressure, etc.

How it works:

Dippy Duck is a small heat engine consisting of a hollow glass barbell with opposite ends able to seesaw about a knife edge pivot. One end of the barbell is filled with a high vapor pressure liquid. The other end is empty on the inside and coated with absorbent flocking on the outside.

When the flocking is wet, evaporative cooling reduces the air pressure inside the empty end of the barbell, causing the liquid at the other end to get sucked up into it. As the liquid rises...

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Supercooling of Water

Pure water cooled to below 273K without freezing; seeded to spontaneously crystallize.

What it shows:

A liquid can be taken to a temperature below its freezing point if it is cooled slowly and there are no nucleation sites for crystallization to begin. In this demonstration you can create a flask of liquid water at below 0°C that, when 'seeded' by the introduction of a nucleation site (in this case dry ice) will be instantaneously frozen.

How it works:

This is pretty much described in Setting it Up.

...

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Thermal Expansion

Brass ball doesn't fit through brass ring until ring is heated.

What it shows:

Most solids (see Comments) expand when heated due to increased atomic and lattice vibrations. In this demo, a brass ring expands when heated to let a previously too small a ball pass cleanly through.

How it works:

The apparatus consists of a brass ring on a handle (figure 1), attached by a chain to a brass ball. Demonstrate that the ball is too large to pass through the ring, then heat the ring over a blue Bunsen flame for about a minute. The...

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Spherical Blackboard

What it shows:

You can use a spherical blackboard for many things, including the teaching of geographical coordinates, as a model for a closed Universe, or simply as a mathematical shape.

In the non-Euclidean geometry of the sphere, a circle will have a circumference greater than 2πr and an area greater than πr2. A triangle’s angles will add to more than 180°, and two parallel lines, called Great Circles, will converge.

A Universe with a density parameter Ω greater than unity will have too much mass to overcome its own gravitational...

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Saddle Shape Universe

Curved space segment for open universe geometry.

What it shows:

Whether the Universe continues to expand forever or will collapse back in upon itself depends upon the amount of matter it contains. For a density parameter Ω less than unity the Universe will not have enough mass to collapse and will be in a state of perpetual expansion. In general relativity, the curvature of space is dependent upon the density of the Universe, and for Ω<1 the curvature is negative or hyperbolic. It can be represented two dimensionally (see Comments) by a saddle...

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Gravitational Field Surface

1m diameter rubber sheet acts as curved space for ball bearing masses.

What it shows:

In general relativity, gravity is replaced by a curved space geometry, where the curvature is determined by the presence and distribution of matter. Objects move in straight lines, or along geodesics, but because of the curvature of space, their paths will simulate the effect of gravitational attraction. This demo gives a two dimensional view of warped space.

How it works:

In this 2-D analog, a 1 meter diameter piece of dental dam forms a...

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Gravitational Lens

Laser and plastic lens with curvature to simulate bending of light by massive object.

What it shows:

Gravitational lensing is caused by the bending of light rays by the gravitational field of an intervening object. The effect is seen with the Sun, but is most spectacular when a whole galaxy acts as a lens to a cosmologically distant object, such as a quasar. Depending on the geometry of the alignment and the structure of the lensing galaxy, the image of the quasar is distorted into two or more distinct images, sweeping arcs or a complete ring. Here we model...

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Faraday Induction

What it shows:

The mathematical description of electromagnetic induction as formulated by Maxwell and Faraday requires two different sets of equations to calculate the induced voltage, depending on whether the coil is stationary and the magnet moving or vice versa. In fact, as this demonstration shows, the voltage is the same as predicted by the two sets of equations.

How it works:

The apparatus is identical to demonstration Faraday's Law, and is described in detail there. Briefly, it consists of a galvanometer hooked up to a...

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Cloud Chamber

What It Shows

The path of a single charged particle can be made visible in cooled supersaturated air/alcohol vapor.

How It Works

The cloud chamber was developed by C.T.R. Wilson at the turn of the...

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