Presentations

Collapsible Cow

What it shows:

A small crude spindly model of a cow is able to support five times its own weight. Another model, scaled up exactly six times in all dimensions, collapses under its own weight! Assuming that strength is proportional to cross-sectional area (∝ dimension 2) and weight is proportional to volume (∝ dimension 3), simply scaling the model up geometrically leads to the situation where the weight is too great for its strength.

Triboelectric Effects

What it shows:

As long ago as 600 B.C., the Greek philosopher Thales knew that amber, when rubbed, would attract bits of paper and other light objects. Many other substances have this same property and can be electrified by rubbing. The kind of electrification (positive or negative) depends on the substances used.

Hand Cranked AC Generator

Observe the induced current in a gimbaled coil as it rotates in Earth's magnetic field.

What it Shows

A changing magnetic flux through a circular coil of wire induces a current in the wire. By spinning a circular coil of wire at constant frequency and measuring the induced voltage across its ends we can find the local direction and magnitude of the Earth's magnetic field as it passes through the coil. The commutators of the coil are configured to produce an alternating current.

Infra-Red Projector

What it shows:

Like visible light, invisible infra-red radiation can be refracted by lenses to produce an image on a screen. Indeed, a slide projector designed for visible light is used as the imaging device; a heat- sensitive screen makes the invisible IR image visible.

Kepler's Machine

Working model to show Kepler's 1st and 2nd laws and the equivalence of the area law to the law of equants.

What it shows:

A demonstration illustrating the equivalence of Kepler's second law, the Law of Areas, with the Law of Angles.

Liquid Nitrogen Marshmallows

A big insulated bowl is filled with liquid nitrogen and marshmallows, which when frozen, are eaten in spectacular fashion.

Regular size marshmallows. Use wooden spoons, big bowl with holes for draining. Push down the marshmallows in the liquid nitrogen and mix to evenly freeze. Serve to volunteers. 

Eaten with open mouth and exhaling slightly gives the effect of dragon's breath.

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