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Hair Raising

What it shows:

A Van de Graaff generator will apply a charge to its dome and anything else in contact with the dome. Should that object be a person, they obtain a net surplus of charge (be it positive or negative). It is especially noticeable with hair, as each individual strand is repelled from every other and from the scalp.

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Electronic Pinhole Camera

What it shows:

The simplest method of controlling light to form an image is to use an opaque mask with a pinhole in it. Rectilinear propagation of light explains all (nearly). A video camera is substituted for the old prototypal shoe box so that an entire audience can see the pinhole image "live."

How it works:

An extremely light-sensitive video camera 1 sans lens substitutes for the pinhole camera box and film. The front of the Newvicon is the image plane and, as this sits right behind the faceplate of the camera...

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Photoelasticity

What it shows:

Normally isotropic substances can become birefringent when under stress. This property can be used in stress analysis.

How it works:

To use birefringence in stress analysis, the sample is placed between two crossed Polaroids. The first Polaroid produces a linearly polarized light source for the sample. This source has components split into ordinary and extraordinary rays; the differing velocities of these rays in the sample creates a phase difference which is color dependent. The second Polaroid takes components of...

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Green Glass Candy Dish

What it shows

How could the fluorescence of the glass in a Crooke's tube generate x-rays? This was the question Henri Becquerel addressed in 1896. His experiments with fluorescence in uranium salts and subsequent discovery of radioactivity are recreated in this demonstration.

How it works

Instead of uranium salts, we use a green glass candy dish—the green glass being uranium glass, a popular consumer item in the 1950's! The green glass fluoresces brilliantly when illuminated by UV (a "black light") and, although not particularly "hot," a Geiger-Mueller counter held...

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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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Elastic Light

What it shows: 

The redshifted spectrum of galaxies and quasars is due to an expanding universe and can be expressed as the ratio of the scale factor of the present Universe to that of the Universe when the light was emitted. You can think of this as the light being s-t-r-e-t-c-h-e-d as the Universe expands so it arrives with a longer wavelength.

How it works: 

A 50cm × 10cm strip of dental dam with a wave drawn on it, attached at one end to a post and the other end free to pull. A wooden dowel at the pulling end ensures...

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Hot and Cold Gas in Balloons

A balloon is dropped in boiling water, and another balloon is cooled with liquid nitrogen to demonstrate the effect of temperature on volume of gas in a balloon.

A 4 liter beaker on a hot plate, with a liter of water boiling within. A prepared balloon, filled with air and tied so that it just fits in the beaker, is dropped into the beaker. The balloon expands to seal the beaker and is forced up by the vapor pressure, ending up on top of the beaker, too large to fit inside.

A foam ice bucket will hold a helium ballon that is large enough to seal around the inside of the bucket...

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Buoyant Force Measurement

What it shows

We have three 20 oz. soda bottles, one filled with water, one filled with sand, and one filled with air. A spring scale shows the water-filled bottle to weigh approximately 6N in air, and nearly 0N when it is fully submerged in a large container of water. Since gravity is still acting on the bottle when it is submerged in the water, there must be a force of 6N pushing up on it. This is the buoyant force.

We can do the same experiment with the bottle of sand. This bottle weighs roughly 13N in air, but when it is fully submerged in water it weighs 6N less. Even...

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Density

Aluminum/Uranium and SF6/Air/Helium comparisons.

What It Shows 

The concept of mass per unit volume is punctuated by having several different substances on hand for comparison. In solid materials, we have equal size chunks1 of aluminum (2.7 g/mL) and uranium (18.7 g/mL) for comparison. For gases, we typically use balloons filled with helium (0.18 g/L), air (1.29 g/L), and sulfur hexafluoride (6.50 g/L). Being 5 times heavier that air, the SF6balloon noticeably feels like it weighs more than the air-filled one and...

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