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Cloud in a Bottle

A 5-gallon bottle containing air and water vapor is slightly pressurized; a sudden release of the pressure cools the vapor, forming a cloud.

The bottle is a heavy Pyrex carboy with tooled mouth. A one-holed rubber stopper fits the mouth and is air-tight. A meter of Tygon tubing is fitted to a short tube in the rubber stopper.

The bottle is kept stopped and wet, and should work off the shelf. If the bottle is dry, spray about 10 ml of distillled water inside.

To demonstrate cloud formation, fit the stopper to the bottle and apply pressure with the lungs. Blow into the...

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Precession Globe

Globe pivoted so north pole can precess.

What it shows:

Due to the oblateness of the Earth, the gravitational force between the Earth and the Sun sets up a couple which causes the Earth's axis of rotation to precess. An adapted globe shows what is meant by precession.

How it works:

An old 8" (19cm) globe has been modified 1 to allow it to precess on its axis. A 23° cone is cut into the south pole, and a cone of metal supported by a metal equatorial ring has been inserted. This makes the globe bottom heavy (and...

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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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Shoot-n-Drop

Ball shot horizontally, one dropped vertically; both hit the ground at the same time.

What it shows:

The horizontal and vertical motions of a projectile are independent of each other. So two objects falling under the influence of gravity from the same height will reach the ground simultaneously, regardless of their horizontal velocities.

...
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Dinner Table

Sliding tablecloth out from under posh dinner setting.

What it shows:

A body will remain at rest unless a force acts upon it. So too will your best china remain in place as the table cloth is whipped from under it providing the friction between the cloth and table setting is low, and the speed of removal high.

...

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Loop-the-loop

A toy car rolling down a loop-the-loop track demonstrates the minimum height it must start at to successfully negotiate the loop.

What it shows:

For an object to move in a vertical circle, its velocity must exceed a critical value vc=(Rg)1/2, where R is the radius of the circle and g the acceleration due to gravity. This ensures that, at the top of the loop, the centripetal force balances the body's weight. This can be shown using a toy car on a looped track.

How it works:

The car is released from the top of a ramp and runs down a slope towards...

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Physical Pendulum

A rigid rod executes simple harmonic motion about an adjustable pivot point.

What It Shows

The period of a physical pendulum is measured and compared to theory. The pivot point, and thus the period, is adjustable along the length of the pendulum making it possible to demonstrate that there is a pivot point where the period is a minimum (stationary point).

How It Works

The physical pendulum is a 1/2" diameter × 100cm long brass rod. A collar with a "knife edge" can be fixed anywhere along the length of the pendulum and serves as the pivot point. The period...

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Acoustic Horn

What it shows:

As a passive amplification device, the exponential horn is amazing. Using a "talking" greeting card as a feeble source of music, the intensity of the sound gets amplified by about 18 dB when the greeting card is coupled to the horn ... a dramatic effect.

How it works:

The multicellular horn is a cluster of eight smaller exponential horns, each with a small mouth to avoid beaming in a large frequency range, but together they form a sector of a sphere large enough to control directivity at low frequencies — the...

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