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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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.

Buoyant Force on Finger

What it shows

An object does not need to float in order to experience the buoyant force.

finger about to push against liquid in a cup

In this example we see a cup of water at rest on a pan balance. When the demonstrator pushes a finger down into the liquid, the buoyant force of the liquid pushes...

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Chladni Plates

Accumulation of sand at nodes of vibrating plate reveals resonance patterns.

What It Shows

A Chladni plate consists of a flat sheet of metal, usually circular or square, mounted on a central stalk to a sturdy base. When the plate is oscillating in a particular mode of vibration, the nodes and antinodes that are set up form complex but symmetrical patterns over its surface. The positions of these nodes and antinodes can be seen by sprinkling sand upon the plates; the sand will vibrate away from the antinodes and gather at the nodes.


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Magnetic Bubbles

What it shows:

A thin wafer of Ferromagnetic Garnet reveals its magnetic domain alignment as light and dark serpentine patterns when viewed between crossed Polarizers. These domains can be flipped by an external magnetic field, changing the pattern structure.

How it works:

The magnetic bubble apparatus consists 1 of a thin (8-12μm) single crystal film of Ferromagnetic Garnet (FMG) sandwiched between a pair of crossed Polaroids. The FMG crystals are magnetically anisotropic, that is, they have a strong tendency to orient...

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Solid, Liquid, Gaseous CO2

Observation of phase changes with corresponding pressure changes.

A two ml. plastic microcentrifuge vial and a small shop vise are used together to melt dry ice.

Wear safety glasses for this demo. The vial can explode, or shoot out of the vice, from the pressure of liquid carbon dioxide. Set up a camera with a close shot of an empty vial before putting in a loaded vial.

Crush a pellet of dry ice to make pieces that fit into the vial. Place a couple of pieces in the vial, and snap the lid closed.

Immediately place the vial horizontally in the jaws of the vice,...

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Conductivity of Solutions

A light bulb is lit when the conductivity probe is immersed in an ionic solution.

The solutions are all in labeled 250ml beakers. All are about 150 ml of 0.1M sol'n. In order, the solutions are: tap water, distilled water, sodium chloride, sucrose, acetic acid, hydrochloric acid, sodium hydroxide, ethanol, and barium sulfate. (See video: http://youtu.be/4WillWjxRWw?hd=1)

The simple conductivity tester is on the bench, for the instructor to plug in. An 800ml beaker with 400 ml of distilled water is provided as...

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Coke Can Buoyancy

What it shows

An unopened can of Diet Coke floats in a tank of water, whereas the same cannot be said for a can of regular Coca-Cola.

photo of fish tank with can of diet coke floating in it

Setting it up

Use the smallest available tank. If unopened cans are not already in the Prep Room, they can be procured...

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Frahm Resonance Gyroscope

Vibrational resonances of metal reeds are excited by a spinning gyro as it slows down.

How it works

The Frahm resonance gyroscope is a standard piece of equipment that can be purchased from science supply houses. 1 It consists of a heavy wheel slightly unbalanced, held in a frame to which seven metal reeds are attached, each having a different vibrational frequency. The wheel is set in motion by unwinding a string that has been wrapped around the axle. As the wheel runs down, it sets each reed successively into vibration as its rotational frequency passes through...

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Hall Effect

What it shows:

When a magnetic field is applied perpendicular to a conductor carrying current, a potential difference is observed between points on opposite sides of the conductor. This happens because the magnetic field deflects the moving electrons (Lorentz force) to the edge of the conductor and the altered charge distribution generates a transverse electric field.

How it works:

The conductor is a small bar (11mm × 2mm × 2mm) of germanium (p-type?). Current (18 mA) is made to flow down the length of the bar by a 3 volt potential...

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