Nitrogen Phase Change

Liquid nitrogen is pumped on and freezes into a sponge of solid nitrogen.

The liquid nitrogen is in a 600 or 800 ml beaker under a shielded bell jar on top of the red vacuum cart. A cold trap is not necessary if only nitrogen is being pumped on.

It is important that the beaker of liquid nitrogen not have frozen water vapor on its side, as the view is impaired. A camera is zoomed in on the beaker, which is in a thick glass bell jar and an acrylic tube shield.

With the pump running and the bell jar vent open, pour the nitrogen and cover the beaker with bell jar. Open up...

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Fakir Physics

The concept of pressure is demonstrated by lying on a bed of nails.

What it shows:

The lecturer (or someone else) lies on a bed-of-nails without discomfort, thus demonstrating the concept of pressure, which is the force per unit area. For added drama the person is sandwiched between two beds of nails with the added weight of a cinder block on top. The cinder block can be broken with a sledge hammer.

figure 1: A supermarket tabloid reports on how macho man pulls off this stunt.

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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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Hand Battery

Copper and zinc plates connected by micro-ammeter; your hand completes the circuit.

Clean copper and zinc sheet metal stock is cut into strips or pads. Alligator clip a zinc strip and a copper strip and plug the leads into a modern multimeter. DC 2V scale should cover the 1.09V that we expect from a zinc/copper battery at standard conditions of 1 Molar electrolyte and room temperature.

Our fingers are a network of electrolytic conductors, with more or less conductance (depending on moisture and salt). Pressed to the metal strips, adjacent fingers complete the circuit and...

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OHP RLC Circuit

What It Shows

The current in a circuit consisting of a capacitor, inductor, and resistor will oscillate back and forth as the capacitor charges and discharges.

How It Works

The circuit layout is shown in the figure below. Initially the knife switch links the capacitor to the battery. Switching to complete the LRC circuit allows the capacitor to discharge. The current I in the circuit increases, as does the magneic field B inside the inductor. When the capacitor charge is zero, I and B are a maximum (the energy of the circuit is now stored in the inductor). As the...

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Tunneling Analog

What it shows:

In quantum mechanics, it is possible for a particle to tunnel through a potential barrier because its wave function has a small but finite value in the classically forbidden region. Here we use FTIR as an optical analog of this quantum mechanical phenomenon.

How it works:

A 45°-90° prism will deflect a beam of light by total internal reflection. When two such prisms are sandwiched back-to-back and pressed together, the air-glass interface can be made to vanish and the beam then propagates onward undisturbed. This...

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Bag of Lead Shot

Dropping bag containing lead turns gravitational potential energy to heat.

What it shows: 

A demonstration of the conversion of gravitational potential energy to heat energy. A bag of lead shot, repeatedly dropped to the ground, will heat up.

How it works: 

Lead has a sufficiently low specific heat capacity (128 J/kg/K) that a 5kg bag dropped five times from a height of 1.0m onto a rigid floor should increase in temperature by about 2K. The shot is contained in a bank deposit bag with reinforced...

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Umbrella decorated with the constellations.

What it shows:

The aberration of starlight is the shift in the position of the image of a star due to the rotation of the Earth about the Sun, and is a consequence of the finite velocity of light. For a star directly overhead, a telescope will have to be angled by v/c to the vertical where v = velocity of the Earth in space, in order that the telescope be pointing at the star. The equipment necessary to show aberration is one umbrella.

How it works:

The best way to picture this...

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