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Creep of Lead

What it shows:

A metal under stress will not fracture straight away, but will deform plastically due to the dislocation of crystal boundaries; this is called creep.

How it works:

Here we use lead as the test sample because there is significant creep compared to other metals. The lead is loaded (see fig.1) to a value that is just below the breaking stress of the sample. When creep occurs, the lead is drawn thinner at its weakest point (called 'necking', see fig.2) until its reduced cross-sectional area causes the sample to exceed its breaking...

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Fracture Strength of Chalk

What it shows:

This demonstration allows you to compare chalk’s compressive strength with its tensile strength.

How it works:

We use railroad chalk, which although being softer and harder to work, is nice and big and easy to see. A sample is placed in each of the two types of testing assembly (details in Setting it Up), and loads carefully applied. Railroad chalk has a tensile strength of 195kNm-2 ± 30kNm-2 (a load of 2.5 to 3.5kg) and a compressive strength of 500kNm-2 ± 65kNm-2 ( a load of 7 to 9kg).

...

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Toilet Paper

What it shows:

The speed with which you tug on a toilet roll determines whether a sheet breaks off, or the roll simply unravels.

How it works:

The force applied to the junction between the sheets of a toilet roll is proportional to the rate of change of momentum of your hand as you tug at the end. Thus a sharp tug (large ∆p) is sufficient to surpass the breaking stress of the perforated junction. A lesser tug however, below the breaking stress, will apply a torque to the roll itself; the ensuing rotation unravels the roll.

figure 1. Toilet roll...

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Potential Well

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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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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Friction Blocks

Selection of blocks that slide down a variable-angle inclined plane to demonstrate the various aspects of friction.

What it shows:

There are actually three (or more) demonstrations under the wing of this title: (1) A block or box is placed on an adjustable inclined plane which can be raised until the block slides. The tangent of the angle then gives the coefficient of friction between the surfaces. (2) The difference between dynamic and static friction may be demonstrated. A large dial spring balance is used to determine the forces required to drag a box on...

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Three-Legged Table

Triangular table supported by platform scales.

What it shows:

This is a two-dimensional version of the Loaded Beam demonstration.

How it works:

An equilateral triangular-shaped table is supported at each corner by a platform scale (same type as in "Loaded Beam"). One of our large (14.5 kg = 32 lb) weights is placed on the table. The scale readings vary with the position of the weight. The procedure to be followed in this demonstration...

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Vector Arrows

Wooden arrow vectors, hand held or mountable.

What It Shows:

Various length and color, wooden arrow vectors can be hand-held, placed (magnetically) on the blackboard, or stuck into a wooden block to define a coordinate system. Small vector blocks can be used as body axes or to visualize coordinate transformations.

...

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Density

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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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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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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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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