Presentations

Copper and Bulb

Copper has positive temperature coefficient; light bulb gets brighter when copper leads are dipped in liquid N2.

What it shows: 

Copper has a positive temperature coefficient (≈ 3.9×10-3 per ˚C), which means that its resistance drops with temperature. Here copper wire is immersed in liquid nitrogen (77˚K = -196˚C), decreasing its resistance (from room temperature) by almost a factor of 2, thus increasing the current flow though a circuit.

How it works: 

We have a coil of 30AWG copper wire...

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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.

How it works:

In order to determine the orbit of Mars using circular orbits, Kepler had to offset the focus of Mars' orbit from the Sun to a point C (figure 1). Kepler's 2nd Law of planetary motion states that a planet's orbit around the Sun will sweep out equal areas in equal times....

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Precipitation of Silver Chloride

Sodium chloride solution is added to silver nitrate solution and a white precipitate of silver chloride is instantly formed.

The silver nitrate solution is around 0.1M, and the sodium chloride solution around 0.5M. Pour the sodium chloride sol'n into the silver nitrate to avoid leaving traces of silver nitrate in the empty beaker.

Wear safety glasses and gloves to prepare and perform this demonstration.

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.

Ptolemaic Epicycle Machine

What it shows:  Long before the time of Copernicus, the Greek astronomer Claudius Ptolemy created a model of all the planets' observed celestial motions. The model involved combinations of perfect circles rotating with uniform speed. Ptolemy explained the apparent "looping motion" of the planets by placing the center of one rotating circle, called the epicycle, which carried the planet, on another rotating circle, called the deferent, so that together the motions of the two circles produced the observed looping motion of the planet. Moreover, the...

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Cannon Ball Boat Puzzler

What it shows

Does the level of the ocean rise or fall when a cannon ball is tossed overboard? A question of displacement.

How it works

A difficult effect to see at sea, but it becomes clear by taking some parameters to extremes. Reducing the ocean to 12L in volume, and the boat to practically no mass by using a plastic bowl, a cannon ball of 1kg mass suddenly becomes substantial. With the cannon ball in the boat, its weight is distributed throughout the boat; the lowered density increases the amount of water displaced (by the fraction of the boat submerged), raising...

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Pulley Board

Upright board or Blackboard Mechanics with pulley combinations.

pulley board

Reaction on Conveyor Track

What it shows:

A straightforward demonstration of Newton's 3rd law, that forces are interactions and thus come in pairs.

How it works:

Two people, each sitting (cross-legged) on their own board, position themselves in the center of the track facing each other. Upon pushing against each other with their hands, they glide apart down the length of the track. Repeat this with one person turned around — the other person pushes on his/her back instead of pushing against each other with their hands. The ensuing motion down the track is exactly the same as before.

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