[★★★]

Great

Chaotic Waterwheel

What it Shows

We start with a vertical wheel—like a Ferris Wheel, but with a diameter just under 1 meter—in neutral equilibrium and free to rotate in either direction. From the ends of each of the eight spokes hang small buckets with drainage holes cut out of the bottom. Fixed directly above the center of the wheel is a faucet connected to a pump.

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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...

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Bean Buoyancy

What it shows

Objects with a density lower than the fluid that they are submerged in will float; objects with a greater density will sink. This is shown using a brass ball and ping-pong ball of equal size, and a sea of beans.

How it works

500g of navy beans form a rather coarse fluid in a 1.5L glass beaker. Embedded in the beans is a ping pong ball, and sitting on the surface is a brass ball, 4cm in diameter. This fluid needs to have flow 'induced', and this is done by shaking the beaker side to side. The ratio of densities of brass:beans:ping-pong is approximately...

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Archimedes' Principle

What it shows

Archimedes' principle states that the buoyant force or upthrust is equal to the weight of fluid displaced. An object with equal mass but a lower density occupies more volume so displaces more water; it therefore experiences a greater upthrust.

How it works

This demo compares the buoyant force acting on two 1kg masses, one of aluminum and one of brass. Each in turn is lowered into a beaker of water using a spring balance (figure 1). The aluminum, having the lower density, experiences the greater upthrust and a reduction in weight from 10N to about...

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Bernoulli's Principle

What it shows

The relative velocities of two sides of a spinning ball to an oncoming wind creates a pressure difference and therefore a net force on the ball perpendicular to the air flow.

figure 1. Direction of motion of ball due to pressure difference

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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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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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Mixing Ethanol and Water

Ethanol and water are mixed in volumetric glassware, showing a volume decrease and a temperature increase.

Two 250 ml graduated cylinders are filled to the line with water and ethanol (100%). A temperature probe shows both at room temperature. The temperature probe is then moved to an empty 500 ml graduated cylinder, and the contents of the two smaller cylinders poured simultaneously to mix well. 

The temperature of the mixture rises about 8°C, and the volume decreases to 480 ml just after mixing, clearly visible on the scale of the 500 ml cylinder, and to the class by...

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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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Vacuum Infusion

A vacuum is drawn over a beaker of sliced cucumber covered in a clear dressing. The cucumber outgases, making bubbles. When the atmosphere is readmitted, the dressing is forced into the cucumber, rendering it translucent and seasoned. 

A polycarbonate bell jar with a volume of about three liters is centered on the base, with attention to the seal. The vacuum pump tube ID is the same as the outlet tube OD, so attach by hand. Vacuum release by sliding the vinyl tube off of the outlet. 

The vacuum pump is the oil-less variety, and is not bothered by water. The pump is...

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Iron Tin Reaction Kinetics

Dark red iron[III] solution is rapidly reduced to colorless iron[II] by addition of tin[II] chloride solution, with the rate depending on concentration and temperature.

Four medium footed cylinders are prepared with 100 ml of ferric chloride solution 0.01M with potassium thiocyanate solution added to make the dark red complex. One of the solutions should be hot, so just the iron and thiocyanate solutions in that cylinder, with a 150ml beaker for the demonstrator to fill with hot water from the water cooler, right before the demonstration.

The cylinders are on the bench top in...

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