so with that in mind, why are lightened flywheels beneficial? quickness?
rather, than top speed/sustained speed?
MAYBE I perceive (cap'n)
-----Original Message-----
From Timothy H. Collins [mailto:thcollin at mtu.edu]
Sent: Wednesday, January 21, 2004 6:52 PM
To: spridgets@autox.team.net
Subject: Puzzler
OK, so here's a new puzzle as it looks like you guys and gals enjoy them.
Two cars are identical and sitting on an incline that is adjustable. One
car has skinny little tires while the other one has huge skins, but all
tires have the same coefficient of friction. The cars weigh exactly the
same.
The parking brakes are set on both cars.
The incline is raised on one end until the car or cars begin to slide.
Which one will slide first?
[The answer is that they will both slide at the same time because static
friction is not area (of the tires) dependent. The key factors are the
coefficient of friction and the weight of the object for static friction -
not area.]
If the above is so, then why do race cars have big tires?
[The answer is that dynamic friction is a whole different critter. Size
does matter here. Just think about it this way. Say you are pushing a full
file cabinet or refrigerator. It takes quite a bit of effort to get the
thing moving, but once it is moving, it is easier to keep it moving. You
have crossed the boundary from static friction rules to dynamic friction
rules.]
Students have a hard time with this at first, but I know this group will
pick up on this right away! <grin>
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