Ice in Water and Ethanol

Ice in water at 0°C is strained and added to a room temperature, 50% ethanol in water mixture. Stirred with a temperature probe, the iced mixture reaches -2°C. 

The stainless steel temperature probe is connected to a Vernier Labquest Mini and LoggerPro software displays a record of the temperature.  Two probes can be used, one in the ice water, and one in the room temperature alcohol. 

Instead of beakers, thick walled pint glasses are used. A strainer and bowl are needed for straining the ice from the water, showing that the same ice melting in water at 0°C...

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Jaw Models

Cardboard animal jaws as examples of levers.

What it shows:

The biting force of an animal depends upon the magnitude, direction and point of application of forces exerted by the jaw muscles. A mammalian jaw exerts a greater force than does a reptilian jaw despite a more delicate joint structure, because evolution has improved the physics of eating.

How it works:

The demonstration consists of two dimensional cardboard models of reptilian and mammalian lower jaws (see figure 1). Both are about 30cm in length. They are pivoted...

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Three Dumbbells

Lecturer rotates on turntable whilst holding two dumbbells.

What it shows:

Angular momentum, the product of a body's moment of inertia and angular velocity, is always conserved. A reduction in moment of inertia will result in a proportional rise in angular velocity.

How it works:

A volunteer holds the other two dumbbells 1 in each hand and stands upon a rotating platform. 2 With arms outstretched and a little push they begin to rotate at a certain angular velocity. By pulling in their arms to their chest, the moment of inertia is...

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Pascal's Paradox

What it shows:

Three containers are filled with water to the same depth, and each has the same base surface area (see figure 1). Since the pressure and area are the same in each container, the force should be the same (pressure = force/area). pascalSo how come the scales...

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Standing Wave in Metal Rod

An aluminum rod, supported in the middle, rings for a long time in its longitudinal mode.

What it shows:

Longitudinal standing waves in solids.

How it works:

A metal rod is not unlike an organ pipe with both ends open. Holding it exactly in the middle will force the simplest, or fundamental, mode of vibration -- the ends will be free to vibrate maximally and the center will be a node. The fundamental frequency happens to be 2.26 kHz. As with a pipe open at both ends , the rod will vibrate at all the odd as well as even...

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OHP Circuit Board

What it shows:

This demo allows a lecturer to play around with various DC circuits on the overhead projector.

How it works:

A removable template of 26cm × 17cm plexiglass has a set of 6mm diameter tightly wound springs of length 1cm fixed at 5cm intervals (reminiscent of those Radio Shack® n1000-in-1 electronics kits). Standard resistors and 5cm lengths of 22AWG wire clip into these springs to form a circuit, and the template is then rested on a parent board consisting of two transparent meters (figure 1). These are...

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Jumping Ring

Shoot the ring through the roof after dipping it in liquid N2; Lenz's law induced EMF in metal ring.

What it shows: 

The induced current in a metal ring is dramatically increased by lowering the ring's temperature.

How it works: 

Here is an extension of the ...

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Earth's Magnetic Field

OHP representation of lines of force using bar magnet and iron filings.

What it shows:

The magnetic field lines of the Earth can be represented by the field lines of a bar magnet.

How it works:

The Earth's magnetic field is basically a magnetic dipole. It can therefore be represented to first approximation by the field of a bar magnet. The shape of the field lines can be highlighted by the sprinkling of iron filings, or by the use of plotting compasses. The latter method has the advantage of showing the variation of dip...

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