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#0823: Lillian and the Thousand Dollar Valve

Original Air Date: 06.07.2008

   Best Moment

Is this Car Talk or "60 Minutes"? This week, 83-year old Lillian turns to Tom and Ray to help decipher a suspicious diagnosis from her usually trusty mechanic. Does he really want to charge her a thousand bucks to replace a valve? Has he succumbed to the beginning of boating season? You won't want to miss it, as our hosts go to the source to try to get the truth. Meanwhile, our Physics advisor Wolfgang is on-hand to administer a (well-deserved) dope slap to the boys for their (wacko) theory on head-on collisions. Also, what do you do when your Maxima's windows go cuckoo? If you're Adam in Baltimore, blame your girlfriend! All this, plus Tommy communes with nature and winds up paying for it in our new Puzzler, and lots more, this week on Car Talk.

Review this Show | 15 Reviews | Need Help Listening? View Call Details

This Week's Puzzler

Tommy spills a basket of eggs. What's the smallest number possible? Find out!

Last Week's Puzzler

From Ray's dining and dancing series: why was he still hungry, even after going to the restaurant? Find out!

Show Open Topic

How you know when it's time to trade in your car, part two.

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Show Review - 425

by ttrikalin

Show Review - 429

by Artie D

Show Review - 431

by Anonymous

Show Review - 434

by Anonymous

Show Review - 435

by Ross

Show Review - 717

by datribble

You Bozos Still Have it Wrong

by samuelrifman

You and your Harvard professor are completely wrong (again). Your point about momentum transfer completely ignores the fact that the oncoming car is DESIGNED to absorb energy in an impact! Thus it is FAR FAR SAFER to hit an oncoming car at your speed than a wall at twice the speed.

Favorite Moment: Waiting for a duhhh.

Wall vs. Car Issue

by metman

I think that Wolfgang oversimplified the crash issue. If change in momentum was the only factor, every stop sign would be a catastrophe. Time must be considered as factor for damage and injury. Relative speed at impact favors the wall option and energy absorbed by deformation will favor the oncoming car as the choice.

An Observation

by Ross

Great show, as always.

Favorite Moment: I'd just like to point out that when you were talking to Forrest from Sacramento, one of you asked him when winter ends. He responded, "End of February." One of you then asked, "And when pray tell does it start?" to which the other of you quipped, "About January!" Forrest, now answering seriously, said, "Around Christmas." I laughed when you guys seemed not to notice that this happens to be...right around January!

You need a new professor

by Anonymous

Disregarding any theories about elasticity of the wall or the other car and assuming all things created equal (perfect, elastic collision) just to make the math easy, we'll examine why you need a new professor. And I hate to say this because I had some excellent physics professors, but you should find an engineer. Ok, I didn't hate it that much... In using the momentum (P) as the basis of Wolfgang's theory, he failed to realize that momentum of a system of particles (i.e. car A and car B) is the vector sum of all the momenta. Forces will be equal regardless of your frame of reference, therefore if we hold car B stationary, car A will appear to be oncoming at twice the original speed with twice the momentum. This problem has to be evaluated as a system of both vehicles and can't be simplified to just one vehicle. The energy balance doesn't work if you remove the second vehicle. Your original evaluation was correct: The force of car A (with xmass and yvel) impacting car B (also with xmass and yvel) is equal to car A (with xmass and 2*yvel) impacting an immovable wall as seen from car A.


You know it's time for a new car when...

Yeah, these are unmistakeable.

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