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Hopper Popper

Athletic equipment companies spend many millions of dollars on the development of materials that have desirable elastic properties. Some of the materials are designed to store and release elastic energy (court shoes, baseballs, golf balls, raquetballs, etc), and other materials are designed to absorb and dissipate the energy over a wider surface area and extended time interval (protective padding). Students might want to make suggestions on how "super basketball shoes", or other devices could be created.

Action and Reaction

Action and Reaction forces are responsible for all changes in motion of all objects. In most instances, such as walking, few people give any consideration to the forces involved. In sporting events, however, considerable attention must be given to the delivery of forces (say, in contact sports), so that the reaction forces do not cause self-injury.

Inertia and Impulse

The effects of inertia and impulse are often unconsciously assessed in normal daily motions. This is often only evident when an object to be moved consists of a much greater or smaller amount of mass than anticipated.

Bed-of-Nails

Surfaces designed for human contact are often smooth and flat, or gently rounded in shape. This results in acceptably low pressures when they are used. Instruments designed to penetrate and modify objects utilize sharpened points or edges to create a very high pressure in a very small region. Pins, picks, and knives are examples.

Barrel Crunch

Scuba divers must be very attentive to changes in pressure when surfacing. As they ascend, they must be certain not to hold their breath! Otherwise, their lungs could behave very much like the balloons in the bell jar. There is no such concern for skin divers, as the air in their lungs will never occupy more space than when they filled their lungs at the surface.

Anyone who has experienced air travel has likely noticed an uncomfortable sensation in their ears as the plane ascends and descends. Air pressure in the cabin changes more rapidly than the air trapped in cavities within the ears. Unequal pressures on the inside and the outside of the ears can be quite painful. If you happen to have a head-cold when flying, you might also notice extra discomfort from the sinus cavities.

Suction Cups

If you open a refrigerator door rapidly, you must use force to overcome the partial vacuum you create, as well as separate the magnetic seal from the metal housing. In a room with at least two doors, and with only one door just slightly opened, you should be able to remotely further open or shut the barely-opened door by rapidly opening or closing a different door. In so doing, you are either creating a partial vacuum within the room or pressurizing it.

Balloons in Vacuum Chamber

The act of drawing air into the lungs is accomplished by creating a partial vacuum around the lungs. They then enlarge just as the balloons did in the bell jar, only we can't create a great enough vacuum to cause them to become too large.

Buzzer and Light in a Vacuum

If light didn't travel through a vacuum, we wouldn't receive any radiant energy from our sun. Since sound is experienced as a fluctuation in air pressure by the ears, and is transmitted by the sea of air in which we live, this conveniently allows us to hear even faint sounds from all directions. This is in contrast to light, which must come directly into the eyes. It is very easy to hear something behind you, but seeing it is a different matter.

Pencil Shoot

All projectiles utilize the compressional strength of their material to penetrate their target with a shearing force. This principle allows a nail to be hammered cleanly through a piece of wood, with very little damage to the wood surface, other than the entry and exit holes.

Vortex Generator

Although the vortices are not generally visible, automobiles automatically generate vortices as they move through the air. Since vortices accompany turbulent, rather than streamline flow, this robs the vehicle of its energy of motion through frictional drag. To obtain better mileage, car manufacturers design cars' shapes to minimize vortex formation.

Laser Light Show

Even though the mirror on the speaker cone cannot be seen to move with the unaided eye, a reflected laser beam greatly magnifies this motion if it is observed on a surface sufficiently distant. Searchlights at airports utilize the same principle and sweep over distances of hundreds of miles in just a few seconds on a clear night, even though the searchlight itself rotates at a very modest speed.

Van de Graaff Generator

A situation similar to the Van de Graaff generator is extremely common in our everyday word. As car tires roll on the highway, they can develop a very large charge due to friction. Fortunately, part of the material used to make the rubber in tires appear black (without coloratives, rubber would appear white) is also somewhat conductive, which allows the electrostatic charge to rapidly drain off through the tires. If this weren't the case, people collecting tolls on tollways would receive large shocks from the drivers. In fact, some new tire compounds which don't readily drain off the charge were recently being tested on the east coast, and tollway collectors immediately began complaining about some very unpleasant shocks. Maybe you could think of ways to put this automotive electrostatic charge to good use.

A common application of electrostatics is the use of electrostatic air filters in residential and industrial heating and cooling systems. As particles pass through grids charged electrostatically to a very high voltage, they become polarized and are attracted to the plates, where they usually become stuck. A simple washing of the grid gets rid of most of the dust. The same principle is used to treat smoke coming from industrial smokestacks. This gets rid of nearly all the ash and other particulate matter, but has no effect on gases which could contribute to various forms of pollution.

Liquid Nitrogen

There aren't very many everyday applications involving the use of liquid nitrogen. Perhaps the most common would involve medical applications. Liquid nitrogen is used fairly routinely by physicians and surgeons to selectively destroy deleterious tissue. Probably the most common instance of this involves the removal of warts. An instrument as common as a cotton swab can be immersed in liquid nitrogen and then held against the wart tissue to cause it to freeze destructively. This can be done with a minimum of damage to nearby, healthy tissue, and the tissue that has been frozen will slough off within a few days.

For more critical situations where damage to healthy tissue must be kept to an absolute minimum, the laser is rapidly becoming the physician's tool of choice. However, for such low-tech applications as wart removal, the use of liquid nitrogen is a much more cost-effective procedure.

Laser PA System

The most obvious real-world examples of optical communications networks are already in use around the world to carry voice, video, and data by means of optical fibers. Optical fibers with a thickness less than that of a human hair are capable of carrying several thousand simultaneous conversations. Optical communications have also been used directly for data transfer within the operating system of computers, but such "wireless" computers have not yet become an economic reality.

If you have any questions regarding Physics on the Road please contact Dr. Keith Adams, Outreach Coordinator (ktadams@purdue.edu).