If this is new to you, you should drink a beer tonight to celebrate a breakthrough in your understanding! This video does an excellent job of explaining it. The textbook is incomplete. One of the advantages of SI is that it clarifies the distinction between mass and force especially weight. In the old British Imperial system there are several options:. It's the failure to state this that leads to the confusion. For most practical cases, a pound mass and a pound weight define the same amount of stuff on the surface of the earth.
There seems to be some confusion here. In the English or American system the "official" measure of mass is the slug. Turns out that And, as someone said, at "standard" gravity 1 lbm exerts 1 lbf on its support its weight.
If you are going to do any significant calculations, it's best, in my opinion, to get rid of all lbm designations and convert everything to slugs. The force required to accelerate 1 lbm In this case, it is in units of slugs.
Know the base units of the unit system you are working in for ANY final solution to be applied appropriately. Both forms are correct! Essentially, 1 , 2 and 3 are all dividing by Know the base units of your system, lbf will always be an ambiguity problem as long as it exists in its current symbolic form. I'd suggest adopting sdl for 2 lbf with unit slug , the ambiguity of pound is an unusual punishment lb, lbs, lbm, lbf, lbf Absolutely, yes you can.
In fact, the mass of a slug is derived from the acceleration due to gravity. I know it is the standard unit for mass and so is lbm. Once you understand this concept well you can go on to familiarize yourself to using slugs. Looking at the last two points above, it is obvious that the newton is very different that the lbf. In the SI system. When you weigh sometime you are measuring a force, yet in SI we record this force in terms of mass kg.
Why we can not create a system that make sense is beyond me. The confusion comes from the English system, we should not ask what is your weight, but what is your mass. Of course this is ridiculous. The confusion comes from an overgeneralization, i. Personally, I think the guy who came up with the pound mass lbm was dyslexic. What I think he really wanted to do was state that;. However, mass and force are a different story. But mass is also specified in pounds. Using one unit — the pound — for both mass and force is inherently confusing.
One variation of the English system of units specifies mass in terms of slugs, but slugs are hardly a common concept. Have you ever purchased 0. The most widely-adopted version of the metric system is the International System of units SI. Measure the mass Find the mass of the object in question in pounds, assuming that this is an object at Earth's surface. If the object is located at the Earth's surface, multiply the mass by the "standard gravitational force" of After multiplying Step 1 and Step 2, the answer is the lbf, the "pound-force" measured in foot-pound per second-squared.
An lbm is a unit of mass called a "pound-mass. For example, a rock that weighs a pound on Earth's surface weighs less on the moon due to lower gravity.
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