Leaning Ladder

Small ladder against wall with variable load and inclination.

What it shows: 

A small ladder is leaned against a vertical wall. A weight can be moved up succeeding steps to find when the ladder will slip and fall down. The forces holding the ladder in equilibrium are in consideration here.

How it works: 

A short (4 foot) step-ladder leans against the wall. The reaction of the wall may be considered horizontal, tangential friction being negligible (the edge of the ladder is covered with a sheet of...

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Double Atwood's Machine

Prediction of motion of masses in a more complex pulley/mass assembly.

double atwoods machine

What it shows:  This compund Atwood's Machine demonstrates an old and interesting problem. The two small weights on the right side are not of equal mass — one is 100 g and the other...

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Spiral Fracture

What it shows:

A spiral fracture is incurred when a torque is directed along the axis of a limb or shaft. Planes perpendicular to the axis are unaffected, but those parallel are twisted, which causes pure tensile forces in one part of the limb, pure compressive forces in another. Fracture occurs when either the compressive or tensile limit of the material is exceeded. This demo shows a spiral fracture in a simulated skiing accident.

How it works:

An old ski boot has a wooden plug placed snugly inside it acting as a foot. A 3 × 4cm square hole accommodates a 0.5m...

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Organ Pipes

Selection of single organ pipes, open and close-ended, to blow through.

organ pipes

Conductivity of Water

What it shows:

Pure water is an electrical insulator. But provide an ionic compound in the form of salt, and you complete the circuit.

How it works:

A simple circuit with the mains supply connected to a 15W light bulb and two copper sheet electrodes (figure 1). The electrodes are placed in a 1500ml beaker containing distilled water. Distilled water is a very good insulator, with an autoionisation of 1:10-7 (the proportion of molecules in H3O+ + OH- form) it has a resistance of...

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Skin Depth

What it shows:

The depth to which electromagnetic radiation can penetrate a conducting surface decreases as the conductivity and the oscillation frequency increase. This demo compares the skin depth of AM and FM radio frequencies, and shows just how small these distances are.

How it works:

An electromagnetic wave entering a conducting surface is damped and reduces in amplitude by a factor 1/e in a distance ∂ given by 1


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Bouncing Light Beam

What it shows:

As a simulation of atmospheric refraction, this demonstration shows the gradual and continuous bending of light due to a gradient in the optical density of the medium. In this case the variable refracting medium is a tank of sugar water with a vertical gradient in the concentration of sugar and a HeNe laser provides the light beam. It can be used as a model of mirage formation (except that the direction of increasing refractive index is in the opposite direction) or even as a representation of the refraction of seismic waves through the Earth's...

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Optical Analog of Uncertainty Principle

What it shows:

In the Heisenberg uncertainty relation, the momentum of a particle cannot be known with any greater accuracy than h/∆x where h is Planck's constant and ∆x is the uncertainty in spatial position. The more you localize its spatial position, the less certain you become about its momentum. An optical illustration for this is the diffraction of light though a slit.

How it works:

For a laser beam, the transverse momentum is pretty well known (i.e. it's zero) but you have no localization of its spatial x coordinate. You...

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