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Standing Wave in Metal Rod

An aluminum rod, supported in the middle, rings for a long time in its longitudinal mode.

What it shows:

Longitudinal standing waves in solids.

How it works:

A metal rod is not unlike an organ pipe with both ends open. Holding it exactly in the middle will force the simplest, or fundamental, mode of vibration -- the ends will be free to vibrate maximally and the center will be a node. The fundamental frequency happens to be 2.26 kHz. As with a pipe open at both ends , the rod will vibrate at all the odd as well as even...

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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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Standing Wave on Long Spring

Obtain as many harmonics as your arm can handle.

What it shows:

Generation of a standing wave by reflection from a fixed end.

How it works:

A two person demonstration using a 2m (2cm diameter) steel spring. 1 One party acts as the fixed end, standing holding the spring rigidly at chest height. The other sends the pulses down the spring by vigorous up-and-down movements. The frequency is adjusted to set up a standing wave from the fundamental up to whatever you're capable of (see Comments). Amplitudes of...

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Shive Wave Machine

Rods attached to metal spine; transverse wave generator shows the reflection of waves free, fixed, terminated and transition boundaries.

What it shows

Mechanical demonstration of transverse standing or traveling waves using the Shive wave machine.

How it works

The Shive wave machine consists of a series of horizontal metal rods 1.25 cm apart coupled by a torsion wire. A pulse can be sent down the machine by displacing the end rods (when doing this by hand, pull down on more than one rod as the connections are delicate and do break). The far...

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Chaotic Pendulum

Coupled, double, physical pendulum executes chaotic motion when non-linear initial conditions are imposed.

What it shows:

A double pendulum executes simple harmonic motion (two normal modes) when displacements from equilibrium are small. However, when large displacements are imposed, the non-linear system becomes dramatically chaotic in its motion and demonstrates that deterministic systems are not necessarily predictable.

...

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Tuning Forks

Selection of mounted tuning forks and rubber hammer.

How it works:

Each tuning fork is mounted on a wooden sound box to amplify the sound (they're very difficult to hear without the box). A microphone/preamp/scope setup may be used to visually demonstrate the pure sinusoidal sound wave. Additionally, a frequency analyzer shows a single frequency component (however, if the gain is turned up high, you may also see the frequency components due to the resonances of the sound box or harmonics of the tuning fork if it was whacked too hard). One of the...

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Torsional Pendulum

Oscillation of mass on wire in torsional mode of oscillation.

torsion pendulum

What It Shows

The frequency of oscillation of a torsional pendulum is proportional to the square root of the torsional constant and inversely proportional to the square root of the rotational inertia.

How...

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Physical Pendulum

A rigid rod executes simple harmonic motion about an adjustable pivot point.

What It Shows

The period of a physical pendulum is measured and compared to theory. The pivot point, and thus the period, is adjustable along the length of the pendulum making it possible to demonstrate that there is a pivot point where the period is a minimum (stationary point).

How It Works

The physical pendulum is a 1/2" diameter × 100cm long brass rod. A collar with a "knife edge" can be fixed anywhere along the length of the pendulum and serves as the pivot point. The period...

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Molecular Size

Also known as the Ben Franklin pond experiment, after a story in B.F's autobiography.

Olive oil with a known volume is dropped onto water. The water has been dusted with lycopodium powder, which floats on the surface. The oil drop expands, pushing the powder aside to form a clear circle, until the oil forms a monolayer. Measuring the area of the monolayer, dividing the volume of the drop by that area, gives the thickness of the monolayer, which is the height of the oil molecule on water.

From our demonstration movie, we found these values. The size of the patch was 62 cm...

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Vortex Tube

What it shows:

James Clerk Maxwell postulated that since heat involves the movement of molecules, it might be possible to separate hot and cold air in a device with the help of a "friendly demon" who would sort out and separate the fast and slow moving molecules of air. The vortex tube is such a device and does exactly that — using compressed air as a power source, it has no mechanical moving parts and produces hot air at one end and cold air at the other.

How it works:

Room temperature compressed air is supplied to the vortex tube...

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Reversible Fluid Mixing

What it shows:

Ink is squirted into a fluid and mixed in until it disappears. By precisely undoing the motions in the reverse direction, the ink becomes unmixed! The demonstration seems to defy thermodynamics in that it appears that entropy decreases, but in actuality the reversible mixing is made possible by ensuring that the mixing/unmixing is done without turbulence.

How it works:

The space between two transparent and concentric cylinders is filled with a viscous fluid (glycerine or Karo™ syrup). One or more lines of...

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