Wheel & Axle Wavefront

wheel & axelWhat it shows:
A mechanical analogy of a wave front consisting of two wheels linked by an axle. It simulates refraction by rolling across a boundary between two surfaces having different rolling friction and thus altered propagation velocities.


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Fishtank TIR

What it shows:

A simple qualitative demonstration of total internal reflection using a laser beam.


How it works:

Using a fish tank suitably doped with a scattering agent (see Setting it Up), a ray of light from a laser beam can probe the water-air...

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Length Measurement

[M | t | ★] 
Standard meter sticks and selection of cubic volumes. 

What It Shows

No temperature-controlled platinum rods here – just some sticks that are very close to a meter in length. Standard meter sticks as well as cubic centimeters and decimeters are available for reference and/or comparison. Other volumes include a 22.4 liter cube (to get the sense of the size of a mole of gas). Sets of calibrated weights include both metric and English standards from milligrams to several kilograms. Various types of analytical balances and scales are also available:...

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Time Measurement

Time signals from U.S. Naval Observatory.

What It Shows

There are several services to help the scientist keep time. Some of these can be brought into the lecture hall. Students can listen to the time signals from WWVB (60 kHz signal from Colorado) on a radio receiver or the U.S. Naval Observatory's time service over a telephone line. A publication giving detailed descriptions of the technical services provided by the National Bureau of Standards radio stations is available in the Prep Room. These services are: standard radio frequencies, standard audio frequencies...

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Potential Well Orbiter

Orbital motion simulated by ball rolling on wooden potential well.

What it shows:

Motion in a central potential is demonstrated by a ball rolling on a circular 1/r curved surface.

How it works:

The 1/r potential well simulates the gravitational potential surrounding a point mass; a ball bearing moving in this potential follows a parabolic or elliptical orbit depending upon its initial trajectory and velocity. As it loses energy due to friction, the orbit decays and the ball spirals towards the centre of the well. You could...

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Galileo's Chandelier

galileo's chandelierBowling ball pendulum with burning candles stuck in holes, used as prop only.

What It Shows

Rumor has it that one day at the cathedral, Galileo watched the swinging of a chandelier after it had been displaced and lit. By using his own pulse as...

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Gravitational Field Surface

1m diameter rubber sheet acts as curved space for ball bearing masses.

What it shows:

In general relativity, gravity is replaced by a curved space geometry, where the curvature is determined by the presence and distribution of matter. Objects move in straight lines, or along geodesics, but because of the curvature of space, their paths will simulate the effect of gravitational attraction. This demo gives a two dimensional view of warped space.

How it works:

In this 2-D analog, a 1 meter diameter piece of dental dam forms a...

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Aluminum/Uranium and SF6/Air/Helium comparisons.

What It Shows 

The concept of mass per unit volume is punctuated by having several different substances on hand for comparison. In solid materials, we have equal size chunks1 of aluminum (2.7 g/mL) and uranium (18.7 g/mL) for comparison. For gases, we typically use balloons filled with helium (0.18 g/L), air (1.29 g/L), and sulfur hexafluoride (6.50 g/L). Being 5 times heavier that air, the SF6balloon noticeably feels like it weighs more than the air-filled one and...

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Saddle Shape Universe

Curved space segment for open universe geometry.

What it shows:

Whether the Universe continues to expand forever or will collapse back in upon itself depends upon the amount of matter it contains. For a density parameter Ω less than unity the Universe will not have enough mass to collapse and will be in a state of perpetual expansion. In general relativity, the curvature of space is dependent upon the density of the Universe, and for Ω<1 the curvature is negative or hyperbolic. It can be represented two dimensionally (see Comments) by a saddle...

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