MadSci Network: Physics
Query:

Re: Can a piezoelectric material absorb impacts?

Date: Fri Jan 31 12:59:42 2003
Posted By: Suzanne Willis, professor,Northern Illinois University
Area of science: Physics
ID: 1043363513.Ph
Message:

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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