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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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Slinky Wave Cradle

Longitudinal wave demo with suspended slinky.

What it shows:

Demonstration of longitudinal traveling waves in a spring. 

How it works:

The Slinky hangs with a bifilar suspension from a rigid thin-walled electrical conduit frame, which is light, strong and cheap. In total, 23 suspension points run the length of the spring; the cord is a thick cotton thread that attaches to a loop of the Slinky with No.10 fishing swivels. The layout of the Slinky and frame are shown in figure 1, but the thread has been...

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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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Big Chladni Plate

What it shows:

A large square metal plate, supported and harmonically driven at its center, is made to vibrate in any one of its numerous normal modes of vibration. As with the regular Chladni Plates, the two-dimensional standing wave patterns are made visible by sand accumulating along the nodal lines. What is different in this demonstration is that a multitude of resonances (across the entire audio range and lower ultrasonic frequencies) can easily be excited. Being a two-dimensional oscillator, the various resonance frequencies are not simply multiples of the...

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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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Driven Damped Oscillator

Single air track glider, with and without variable frequency driver, variable damping, and oscilloscope position vs. time display.

What It Shows

With one end of the car attached via a spring to the end of the track and the other end of the car coupled (via a similar spring) to a driving motor, we can see how the car behaves when it is driven below, at, and above the resonance frequency. Markings on the motor help to show the phase relationships between the driver and car at different frequencies. A storage scope tracks the motion of the car (see Setting It Up...

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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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Circular Motion and Simple Harmonic Motion

Simultaneous shadow projection of circular motion and bouncing weight on spring.

What It Shows

One of the simplest of periodic motions is uniform circular motion. By shadow projecting both uniform circular motion and oscillatory simple harmonic motion onto a screen, one can show that these two seemingly different kinds of motion are actually identical.

How It Works

A 8 cm diameter plastic ball mounted near the edge of a 46 cm diameter disk undergoes uniform circular motion. The disk, oriented vertically, is driven by a 57 RPM motor.1 A large...

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Magdeburg Hemispheres

When evacuated, held together by bombardment of atmospheric molecules.

What it shows:

Two brass hemispheres are brought together and evacuated, and are held together by the pressure of the atmosphere.

How it works:

Two brass hemispheres fit together to form an air-tight seal. One has a vacuum pump attachment and stop cock; the completed sphere can evacuated using a vacuum pump under a minute. As atmospheric pressure is 105Nm-2, the 11cm diameter hemispheres are held together by a force of 15000N. Invite members of your...

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55 Gallon Drum

What it Shows

With an air pressure of 105 Nm-2 at sea level, even a heavy duty oil drum will be crushed if it has nothing inside to balance the pressure.

How it Works

The screw cap on the drum is fitted with a vacuum pump connector. Simply turn on the Varian SD-200 pump and wait—it usually takes a few minutes to pump down, so you can carry on with what you were doing interrupted by various creaks and bangs as the drum's side walls begin to give. Because drums of this size are ribbed for strength, they can hold up under the strain, but when it...

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Inverted Pascal Experiment

What it shows:

This is a concept question relating to Pascal's cask-bursting experiment. Imagine the experiment inverted—literally! Attach a 20-ft length of tubing to the opening of a can full of water. Turn the can upside down and raise it high. Will the water stay in the can, or will it run out? Will atmospheric pressure hold up the column of water in the tubing? What will happen? Have the class vote.

...

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Golf Ball Atmosphere

A model of molecular motion and pressure using practice golf balls.

What it shows:

The kinetic energy of gas molecules bouncing off a surface causes pressure.

Increasing the molecules' speeds increases the pressure and the volume of the gas.

 

How it works:

Plastic practice golf balls represent...

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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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