[★★★]

Mixing Ethanol and Water

Ethanol and water are mixed in volumetric glassware, showing a volume decrease and a temperature increase.

Two 250 ml graduated cylinders are filled to the line with water and ethanol (100%). A temperature probe shows both at room temperature. The temperature probe is then moved to an empty 500 ml graduated cylinder, and the contents of the two smaller cylinders poured simultaneously to mix well. 

The temperature of the mixture rises about 8°C, and the volume decreases to 480 ml just after mixing, clearly visible on the scale of the 500 ml cylinder, and to the class by...

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Stack of Blocks

A dozen blocks are stacked on top of each other over the edge of the table seemingly defying gravity.

What it shows:

N objects of unit length can be stacked on top of each other so that the top object sticks out over the edge of the lecture bench by a distance equal to 1

1/2 + 1/4 + 1/6 + 1/8 + ... + 1/(2N)

For N approaching ∞, the diverging infinite sum suggests that the top of the pile can stick out an infinite distance. In actuality the divergence is slow, 2 and our more practical stack of a dozen 2 × 4 "blocks" can...

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Spiral Fracture

What it shows:

A spiral fracture is incurred when a torque is directed along the axis of a limb or shaft. Planes perpendicular to the axis are unaffected, but those parallel are twisted, which causes pure tensile forces in one part of the limb, pure compressive forces in another. Fracture occurs when either the compressive or tensile limit of the material is exceeded. This demo shows a spiral fracture in a simulated skiing accident.

How it works:

An old ski boot has a wooden plug placed snugly inside it acting as a foot. A 3 × 4cm square hole accommodates a 0.5m...

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Vibrating String

A 1.5m length of string driven at one end and fixed at the other shows standing waves for various driving frequencies.

What it shows

vibrating string

The fundamental is the most dramatically visible state (usually around 15Hz). It's possible to show up to 8 nodes clearly--bearing in mind...

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Benjamin Franklin's Thunder House

A replica of Franklin's Thunder House demonstating the efficacy of his invention—the lightning rod. The class will get a charge out of this one.

thunder house

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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Street Lamp Spectra

What it shows:

Unlike the continuous spectrum emitted by blackbody radiators, the light given off by atoms in a gaseous discharge is characterized by its discreet nature. Using street lamps for the light sources, bright atomic spectra of mercury or sodium are projected onto a screen.

...

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Seismic Wave Refraction

Total internal refraction of laser beam through sugar solution with refractive index gradient; representative of seismic waves through Earth's mantle.

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...

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