Presentations

Inverse Square Law

[XL | t++ | ***]  inverse square law, luminosity

What it shows:  The intensity of light from a point source decreases as 1/r2, where r is the distance from the source.

How it works:  For the point light source, we use a 1500 watt clear light bulb. The detector is a small solar panel.1 The output current is directly proportional to the intensity of the light falling on the panel and the current is displayed on an analog milliameter. (The current can also be measured by a digital meter or computer.) Measured...

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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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Erector Spinae Muscle Forces

A realistic model of the forces in the erector spinae muscles that support the back when bent over.

What it Shows:

This is an analysis of the tensions in muscles and forces on joints as an application of torques in static equilibrium situations. The muscles involved in supporting the human torso in a stooped position are realistically modeled, and the extraordinary large forces calculated and demonstrated.

How it Works:

When bending over into a stooped position, the principal muscles which support the back are the erector...

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Bosun's Chair

Block and tackle, or a simple pulley, attached to hall ceiling for lecturer to hoist self.

bosuns chair

Reactionary Roadbed

Radio controlled car moves one way while road moves the other.

What it shows:

We tell our students that, when a car drives down the road, the road and the Earth move in the opposite direction, albeit imperceptibly. This demonstration is a realization of that concept, made possible (and perceptible) by the fact that the road is not attached to the Earth.

...

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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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