| MadSci Network: Physics |
Hello, Joel! Interesting question! Yes, the piezoelectric material would probably convert some of the kinetic energy of the car to electrical energy. This would not particularly help reduce injuries to the occupants, though. Why not? Because the car is going to go from full speed to zero when it hits the tree; whether its kinetic energy gets transformed to heat, sound, electric energy, is not the issue. The issue is, how fast do the occupants of the car go from full speed to zero? This is described by the impulse, which is the force multiplied by the time, and is equal to the change in momentum (mass times velocity). In equation form: Ft = mv (assuming you are going from mv to zero). So if the occupants stop in a short time, the forces on them must be large; if the time is longer, the forces are smaller. Cars are therefore designed so that they crash ?slowly?, by crumpling (preferably in such a way as to not further injure the passengers). Seat belts serve to attach the occupants to the vehicle, so they slow along with it (rather than slamming into it all at once); air bags slow the impact of the occupants further. In any case, piezoelectric crystals are rather expensive, and would shatter on impact (breaking the electrical connection). Here are some sites about piezoelectricity: Piezoelectricity: http://www.ortho.lsumc.edu/Faculty/Marino/EL/EL4/Piezo.html Hot topics: Piezoelectricity: http://www.discoverchemistry.com/dcv2- Piezoelectricity: http://www.tedlind.net/Piezoelectricity.htm Fundamentals of Piezoelectricity and Piezo Acutators: http://katalog.physikinstrumente.com/Links/topicPDFs/4-15_17.pdf Rice Audio © Piezoelectricity: http://mywebpages.comcast.net/riceaudio/html/Piezoelectricity.html Piezoelectricity and Pyroelectricity: http://www.spme.monash.edu.au/teaching/msc3011/elec_&_opt(7).pdf PIEZO! http://stage.itp.nyu.edu/~ap842/Piezoelectricity.htm And some about the physics of automobile crashes: Google Automotive Safety Directory (lots of links): http://directory.google.com/Top/Science/Technology/Safety_Engineering/Autom otive_Safety/ Modeling Real World Events: http://nzip.rsnz.govt.nz/ZollmanModelling.pdf Getting Students to Use Seatbelts: http://irascibleprofessor.com/comments-4-3-00.htm Crash Test Challenge: http://www.cps.k12.ri.us/~whills/mckenna.html
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