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Letters to the editor
By Design News Staff -- Design News, December 20, 1999
Checked your units lately?
I agree wholeheartedly with Paul Teague's comments on the NASA communications goof, in his 11/15/99 editorial, "To err is human; so is talk." But the underlining cause is slightly more basic than even he indicates.
A number without units is meaningless (except for some cases with zero). In high school I had a Physics teacher who constantly was harping on units. The only way you could pass her class was to show the units with the formulas, as well as with the final answer. At the time it seemed silly, but I did what she required so I could pass.
Few things in my education have served me better than the lesson she drove home about always using units. In the 18+ years I have been doing engineering, I have seen more and more young engineers who haven't learned how easy it is to think you have a correct answer only to forget to apply some unit conversion.
If anyone thinks that universally switching to the Metric system will eliminate stupid errors (like the one that caused the Mars Lander to be lost), they are sadly mistaken. Is a meter the same as a kilometer? Of course not! Without units, no one knows what a number really means.
Kevin Acheson
Chief Engineer
The Gear Works-Seattle
Windshield 101
In response to reader Mr. Carlos DeCarvalho's idea of mounting auto windshields (Design News Letters 11/15/99) using a shingling effect along the top to prevent water leaks and three clamps to cause the glass to bear down on a gasket, I believe he is overlooking a few things. Glass is a liquid and a piece as large as a windshield expands and contracts a great deal with heat and cold, and it seems as if the clamping would constrain it to the breaking point.
Windshields are now mounted on a gasket surface made of a mastic type material applied to the surface of the glass and the metal framework of the car body before being joined, so the glass floats and is unrestrained during expansion and contraction. Also, though I don't know for sure, windshields are now often part of the passenger side airbag's back support system when deployed and clamping the glass down may be a problem.
Mark Paar
Des Moines, IA
Wonder welder
Just read your article "Adhesive tape finds home on the range" (10/18/99). Viking, the company that switched from a weld process to tape, probably does not realize that Amada just reinvented the spot welder, released in January 1999 in the U.S. We were extremely impressed with the samples they sent us. It does not spark or leave a nasty weld and no rework is required. Works with aluminum, steel, copper, titanium, and other materials. Check it out at www.amada.com. Enough said -- I love it!
Ed Young
Allstyle Coil Co.
Houston, TX
No videos for this vacationer
I can't help but comment on the photo (Design News 10/4/99, page 88) showing two children wearing earphones and watching videos in a GM van.
Four years ago, my wife and I and our four children, ages ten through seventeen, spent three weeks on a road trip through Nevada and California. Prior to starting out, we informed the kids that their tape players would remain at home.
Amazingly, the trip went very well and it's interesting just how much the kids remember from those three weeks. Personally, I believe that paying upwards of $1200 for an entertainment system to keep the little darlings from being bored is a waste, and I see it as causing more trouble than it is worth.
Floyd Stearns
Retired
Eastman Kodak Co.
First law of Jesse's shoes
In Breaktime (Design News 9/20/99) you posed the problem: What is the optimal footwear design that would allow Minnesota Governor and former professional wrestler Jesse the Body Ventura to jump from a 10-ft. platform into a large vat of uncooked Grade A white eggs and guarantee that none would crack or break?
To solve this problem, you take the number of eggs per cubic ft of fluid in the vat multiplied by Jesse's weight times the fluid density. Then, divide by the volume of the vat multiplied by Jesse's landing attitude (.8 for sunny side up and .6 for over easy). The answer will give you the shoe size divided by .5, times the sole density, assuming a 2:1 aspect ratio and red laces.
Jim Fleming
Motorola
Scottsdale, AZ
CG too high
The choice of jumpers prevents any solution. Years of focus on upper-body weight training have already placed the Governor's center of gravity precariously high. Earlier in his career, he often compensated with a tightrope walker's balance bar hid inside his feathered boa until he reached the ring. Eventually he tried shaving off all his hair to help remove some of this top-heaviness, but to no avail. As a politician, his ego and inflated sense of self-importance have now placed his center of gravity a full 7.3 inches above the peak of his cranium. The result: With any leap, Ventura will almost certainly go plummeting head rather than feet first into the eggs.
If I win, please send my nifty Design News flashlight to the Reform Party, so that they might find a candidate as they walk around in the dark.
Mitchell Smith
Senior Mechanical Engineer and Pundit
Mallinckrodt, Inc.
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