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Musical Bottle

A beer bottle becomes a Helmholtz resonator when air is blown across its mouth.

musical bottle

Bell Plates

What it shows

Bell plates are polygonal-shaped flat pieces of sheet metal which, when held in the hand and struck with a beater, produce a pleasant, sustained, slightly bell-like tone. Compare this to any arbitrary shaped piece of metal which produces a "clunk" when struck. The sound of the bell plate depends strongly on its shape and even the most modest change in the symmetry (like snipping off a corner) or proportions will make it go clunk when struck.

How it works

Why does a particular shape ring so well,...

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Doppler Ball

Plastic Wiffle Ball with built-in shriek to throw past (or at) your audience.

What it shows:

Waves emitted from a moving source are Doppler shifted to higher frequencies when moving toward the observer, and shifted to lower frequencies when moving away. This audio demonstration is also a useful analog to the optical red shift and blue shift exhibited by astronomical sources moving relative to the Earth.

How it works:

A plastic Wiffle-Ball™ is filled with foam padding to protect an enclosed mini-speaker 1 and its...

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Inverted Pendulum

A physical pendulum finds stability in its inverted position when driven at the proper frequency and amplitude combination.

How it works

The physical pendulum is a 45 cm x 2 cm x 6 mm (1/4") strip mounted on a ball-bearing pivot and can rotate 360 degrees. Its pivot is driven by a 3/4" stroke Sears Craftsman Auto Scroller Saw (...

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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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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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Pendulum Waves

What it shows:

Fifteen uncoupled simple pendulums of monotonically increasing lengths dance together to produce visual traveling waves, standing waves, beating, and random motion. One might call this kinetic art and the choreography of the dance of the pendulums is stunning! Aliasing and quantum revival can also be shown.

How it works:

The period of one complete cycle of the dance is 60 seconds. The length of the longest pendulum has been adjusted so that it executes 51 oscillations in this 60 second period. The length of each...

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Simple Harmonic Motion Demonstrator

Relation between circular motion and linear displacement on overhead projector.

What It Shows

Uniform circular motion can be shown to be the superposition of simple harmonic motions in two mutually perpendicular directions. This apparatus gives the audience a visual display of how one dimensional simple harmonic motion varies in unison with circular motion.

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Capillary Action

What it shows:

capillary actionDue to surface tension effects water rises up a narrow bored tube; the rise in height being inversely proportional to the bore's radius.

How it works:

The setup shows the direct comparison between four...

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Double Bubble

What it shows

When two different size soap bubbles are connected together, the smaller diameter bubble will shrink and collapse to blow up the larger diameter bubble. One can use this to demonstrate Laplace's law or the phenomenon of minimizing the surface area of a soap film.

How it works

Laplace's law tells us that the gauge pressure of a spherical membrane is given by 2γ/r, where γ is the surface tension and r is the radius of the sphere.1 For soap bubbles (which have an inside as well as outside surface), the gauge pressure is twice...

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