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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...

What it shows:

Handy size model of a generic spiral galaxy to show salient features or to describe structure of the Milky Way

How it works:

The model is a 30cm diameter Plexiglass disc 1cm in thickness, with a Ping-pong ball stuck through the center to represent the nucleus. The spiral arms of the galaxy are sprayed on with white paint, and we've stuck on a "you are here" arrow pointing to the outer reaches of one of the spiral arms at the approximate position of the Sun in the...

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...

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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Potato Chip Calorimeter

A soda can with 50 ml of water is held over a burning potato chip of known mass. A thermocouple reads the temperature of the water, and its change, to estimate the energy content of the chip.

Other burnable foods include nuts, e.g. brazil nut, and other kinds of fried snack chips.

The heat transfer from burning chip to soda can bottom is only so good, and the temperature rise does not match that expected in the ideal case.

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...

What it shows:

A random walk is a mathematical model for the movement of a particle that is under the influence of some random or stochastic mechanism that affects its direction of movement. Physical situations that can be described by random walks include diffusion and Brownian motion.

How it works:

The board is a two dimensional random walk model consisting of a hexagonal array of corks, ¹ 11 to a side (331 corks in all), with each point of the hexagon given a number. The random walk begins from the center cork and...

What it shows:

The period of a physical pendulum is measured and compared to theory:

non-uniform pendulum

where I is the rotational inertia, g is the...

Wheel & Axle Wavefront

What 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...

Harvard Natural Sciences Lecture Demonstrations

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Demo Subjects

Key to Catalog Listings

214cc242b41c7c56d60acd8c0b8443ef

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