The very first determination of a half-life for a radioactive decay was made by Rutherford. 1 In a study of the properties of thorium emanation, he found that the intensity of the radiations fell off with time in a geometric progression. That historically important result is reproduced in this demonstration experiment. The gas thoron, or thorium emanation, is an isotope of radon (86Rn220) which decays by α emission and has a half life of 55.6 seconds. 2 Using an emanation electroscope, we observe the...
Evaporation of water on duck's head cools vapor inside causing low pressure, etc.
How it works:
Dippy Duck is a small heat engine consisting of a hollow glass barbell with opposite ends able to seesaw about a knife edge pivot. One end of the barbell is filled with a high vapor pressure liquid. The other end is empty on the inside and coated with absorbent flocking on the outside.
When the flocking is wet, evaporative cooling reduces the air pressure inside the empty end of the barbell, causing the liquid at the other end to get sucked up into it. As the liquid rises...
Mechanical properties of some materials change dramatically with temperature. These changes have entertaining effects on everyday objects by taking them from room temperature 300K to the temperature of liquid nitrogen 77K.
How it works:
Place your everyday objects in a dewar of liquid nitrogen for several minutes (at least until the LN2 stops boiling). Some examples to use:
1. Rubber gloves freeze solid and shatter on impact with floor. 2. Use a banana to hammer a nail into wood 3. Frozen...
As demonstrated by two people throwing a volleyball to each other while sitting on rotating platform.
What it shows:
The Coriolis force is a pseudo force existing in a frame that rotates with constant angular velocity to a reference frame. It acts on a body moving in the rotating frame to deflect its motion sideways. Here the audience sits in the reference frame, while two volunteers on a rotating platform experience the coriolis force by trying to basket a volleyball.
A liter of warm water in large pyrex vessel, covered with fine mesh stainless steel screen, is on a stool close by in-floor vent hood. Add a few drops from the phenolphthalein indicator bottle.
Using the long forceps, pick out a pea size lump of sodium metal from the mineral oil in the small beaker. Wipe off the lump on the dry paper towels. With the vent fan running, lift the edge of the screen and drop in the sodium metal. Replace the screen and get back.
The sodium will from a hissing ball of molten metal, which bounces...
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...
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...
The concept of pressure is demonstrated by lying on a bed of nails.
What it shows:
The lecturer (or someone else) lies on a bed-of-nails without discomfort, thus demonstrating the concept of pressure, which is the force per unit area. For added drama the person is sandwiched between two beds of nails with the added weight of a cinder block on top. The cinder block can be broken with a sledge hammer.
figure 1: A supermarket tabloid reports on how macho man pulls off this stunt. ...