- Joined
- Jun 21, 2013
- Messages
- 317
Well, actually, friction applies whether it is constrained or unconstrained. If the surface between the chuck and the backplate had no friction, it would be pretty easy to start moving the chuck sideways-as the first bit of motion would stretch the bolts very little-then as you moved the chuck further, the bolts would begin to stretch more and more for each unit of motion, and it would get more and more difficult to move the chuck.
And I'm not trying to be a jerk, but just because it is common to use the incorrect term, doesn't make it right! (at least, until it becomes so common that the new usage gets put in the dictionary) Also, we are talking about a technical subject here, so I think it's important to use correct terms, especially for the benefit of those who don't know this stuff, and may be confused. It's kind of like quoting torque in ft/lb, which is very common, but totally incorrect. Try plugging it into an equation, and if you don't see the error, you will get completely incorrect units when you are done.
And I'm not trying to be a jerk, but just because it is common to use the incorrect term, doesn't make it right! (at least, until it becomes so common that the new usage gets put in the dictionary) Also, we are talking about a technical subject here, so I think it's important to use correct terms, especially for the benefit of those who don't know this stuff, and may be confused. It's kind of like quoting torque in ft/lb, which is very common, but totally incorrect. Try plugging it into an equation, and if you don't see the error, you will get completely incorrect units when you are done.
It's even more complicated than that. The phenomenon you mentioned is called static and and dynamic friction but that only applies to unconstrained motion. In this case, the bolts are constraining the chuck so, it would take a minimum of 9000lbs (to begin overcoming the static friction and then overcome the bolt tension) to move the chuck. My point was to outline the general principals involved and get folks to realize that you'd need to put the weight of two automobiles on the chuck before anything could possibly happen. I also made a light attempt to show folks how to make simple clamping force calculations. I should have mentioned that the values are taken from a standard chart.
It's pretty common when describing a problem to use the word "force" as an improper noun or as an adverb. The units of the final value take precedent and clear-up any confusion. Many folks say things like "The force of the crash caused damage to the vehicles". -It makes perfect sense but it's wrong. Collision encounters always generate impulses -not forces. -But we still understand what is meant.
Ray