The Basics In Building A Bridge

  When building a bridge, we should consider all the possible types we can make. There are different spans, trusses, and girders we can incorporate into our design, and each has their own strengths and weakness, some more than others. The first step before considering designs, however, should be to identify what the bridge will have to hold, or the use of the bridge, and in what circumstances.

  The four principal terms employed when defining a normal bridge are span, material, the position of the roadway regarding the construction of the bridge, and form. Each term has subtopics that leave us many options with the bridge.

  The first term is span; there are three main types of spans, and these can be made with many different things. The three things are beams, girders, or trusses.  When dealing with an arched bridge, a continuos hinged or simple hinged span will work the best. A span is the distance between the legs of the bridge.  Spans are horizontal and when the term span is used, it could also be relating back to the construction of the bridge itself.

  The second main part of a bridge is a truss. The truss is the roadway of the bridge. The main types of trusses are deck, pony, and through trusses. A deck truss is used when the bridge is a main street, with traffic and many cars. The pony truss is employed if the builder wants the traffic to travel in the middle of two superstructures. Pony trusses, however, are not crossed like and “X” on the top of the bridge.  The last truss is the through truss. With this truss, the traffic would travel underneath the superstructure. Unlike pony trusses, through trusses use cross-bracing.

  In a bridge, the girder is the framework made to hold up the weight. What makes horizontal girders so strong is their stiffness. With this they are able to brace the vertical weight on the bridge. A girder is usually very thick, and is sometimes made up of more than one beam.  

         To strengthen the girder, haunches can be involved in its planning. In a haunched girders are not straight, but rather arched towards the end of the bridge. The constraint of these bridges is their size. On most bridges, smaller beams are used, because they are easier to move around. With this, the smaller pieces have to be joined together, usually by splice plates. 

http://pghbridges.com/basics.htm

http://pghbridges.com/termsBrg.htm

The Physics of Magnetic Nail Polish

Magnets play a key role in the newest and most popular fashion sensation.  The results of the innovative magnetic nail polish are largely accredited to the physics of a magnetic pull.  In most cases, you apply two coats of the nail polish.  The first is left alone and then the second coat is heavily applied once the first application has dried.  Before the second coat dries, you hold a  magnet over your nail for about ten seconds and the results are shown below.

Photo taken from: http://www.thelooksforless.com/2011/09/12/manicure-mondays-layla-magnetic-nail-polish-review-tutorial/

            The appearance of this nail polish changes based on the magnet used.  This is because each magnet has differently arranged atoms.  Although the nature of a magnet is not completely understood, scientists believe that each of the millions of atoms that make up a metal have their own separate magnetic charge.  Magnets have both north and south poles.  The magnets pull towards each other when opposite poles are facing each other (north and south), but when the same sides of two magnets are pointed together (such as the two south sides), the magnets will refuse to come in contact.  The atoms of an unmagnetized metal are facing in many different directions.  In a magnetized metal, all the atoms are pointing in the same direction.

Copyright Explain that Stuff 2008, available under Creative Commons Attribution-Noncommercial-Share Alike license.

            Iron is not an initially magnetized metal, but if held up to a magnet, it will turn into one itself.  When the south end of a magnet is held up to iron, the north end of the magnetic atoms inside of the iron material will pull towards the magnet. This reaction makes the iron magnetic, and is seen in the magnetic nail polish. 

            The nail polish contains iron powder with minuscule iron filings, each of which is turned into a little magnet. They either repel or attract the original magnet and each other.  The filings inside the nail polish are what create the unmistakable pattern.  They move around each other until the magnet used is removed. The magnet applied, the arrangement of the powder, and the position of the magnet above the nail will generate a slightly unique pattern. 

http://www.physicscentral.com/explore/action/nailpolish1.cfm