Ask The Search Engineer

Dear Mr. Search Engineer: I noticed several references to "centrifugal force" in a recent article in Design News. But there's no such thing, right? —Scott in Minnesota

Dear Scott: Actually, you are confused about the distinction between physical forces and inertial forces. The concept of a centrifugal force derives from D'Alembert's principle which takes the acceleration side of the F=ma equation, and moves it to the other side (F-ma=0). This allows a body under the influence of physical forces (F) to be considered in equilibrium with the inertial forces (ma). This approach has some advantages for analysis in certain situations. In the case of motion along a curved path, the term "centripetal" basically means "toward the center of curvature," while the term "centrifugal" means "away from the center of curvature. In curvalinear motion there must be a physical (centripetal) force in the centripetal direction in order to force the body along a curved path. This physical force causes the centripetal acceleration.

Hi There, Search Engineer: We took the plunge and bought brand new hardware and software, specifically a Pentium 4-2 GHz with Windows XP Professional Software. All of my program and data files transferred nicely except I can't get AutoCAD R-13 drawings to print on my HP Laserjet III printer. What's up?—T.E. in Indiana

Dear T.E.: Dude, if you're going to spend money on a computer, put a little extra in the budget to upgrade your CAD software, too. Here's why:

1) CAD upgrades are not all that expensive anymore (provided you are a registered user).

2) Your skill levels will improve, rather than stagnate

3) Since your skill level will improve, so will your marketability (hey, you never know when you might be out of a job these days)

4) You will find it ever increasingly difficult to swap files with others

Oh Wisest of All, Mr. Search Engineer: I have a prototype molding process that involves pouring molten material onto a constantly rotating mold plate. The mold holes are through-holes. Below the moving mold plate is a static chill plate. The problem is "smearing." As the molten material first contacts the chill plate, a thin film is laid down until enough of the material has set up to plug the hole. Any ideas?—J.P. in Chicago

Dear J. P.: The first idea is free, we'll have to bill you for the rest! You could try placing a stainless steel foil "seal" on the bottom of the moving mold plate. Alternatively, silicone grease or other viscous compound might serve to temporarily "attach" to the seal, preventing the leakage while giving the necessary cooling. Or, how about rotating or moving the chill plate so that it can be cleaned, scraped or lubricated during the process? You might even try welding a thin plate to the mold between the chill plate and the mold. The thin metal plate should not cut down cooling too much, and it will block the molten material.

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