Roady
- 9
- 1
- Homework Statement
- Def of lbf=32lbm*1ft/sec^2=1lbm*32f/s^2 So, 1lbf=1/32slug*32f/s^2. But, 1lbm*32f/s^2=32lbf.
- Relevant Equations
- def of lbf=32lbm*1ft/sec^2
Where's the discrepancy?
No it isn't. That contradicts the previous definition.Roady said:But, 1lbm*32f/s^2=32lbf.
No. See if you can spot your mistake.Roady said:But, 1lbm*32f/s^2=32lbf.
That is wrong. The above equation (which I'll call equation A) doesn't follow from the other equations.Roady said:But, 1lbm*32f/s^2=32lbf.
As I pointed out in your other thread, the correct formula for systems of units that are not coherent is ##F=kma## where k is a unit conversion factor. For coherent systems, ##k=1##.Roady said:I've pulled this formula inside out. There are only 3 terms. F=ma
Hmm. If ##x = \frac 1{32}a \times 32b## then:Roady said:The numerical value of rt does not =left. 1lbf= 1/32slug*32f/s^2. Cancel, not multiply 32. Yields,
1slug*1f/s^2 units which is def of pound force, Steve. You just didn't simplify. Nice try.
I love it when a discussion ends in agreement.Roady said:Thank you. I had completely forgot about this constant.
No. There is no officially-sanctioned definition of the pound-force. The definition of the pound Avoirdupois is 0.453 592 37 kg.Roady said:Homework Statement: Def of lbf=32lbm*1ft/sec^2
I would say it sent man to the moon. FORTRAN sent man to the moon. A guess; I wasn't directly involved. 60yrs ago, mks was hardly taught in Am universities.Mister T said:No. There is no officially-sanctioned definition of the pound-force. The definition of the pound Avoirdupois is 0.453 592 37 kg.
The closest definition of the pound-force makes use of the formerly officially-sanctioned definition of the kilogram-force that depended on this so-called standard value of the free fall acceleration g = 9.806 65 m/s2. Thus the pound-force would equal (0.453 592 37 kg)(9.806 65 m/s2).
This is, at least, how NASA defines it.
I've never seen units like the slug or the poundal used anywhere other than a physics classroom.
By the time I went to high school seven or eight years later the science classes were teaching nothing but MKS (or cgs). Like @Mister T, I've never seen a slug or a poundal in the wild.Roady said:I would say it sent man to the moon. FORTRAN sent man to the moon. A guess; I wasn't directly involved. 60yrs ago, mks was hardly taught in Am universities.
The definition I gave based on SI units is indeed the definition of the pound-force used by NASA's manned lunar missions in the late 1960's and early 1970's. I fail to see your point.Roady said:I would say it sent man to the moon.
Roady said:60 yrs ago, mks was hardly taught in Am universities.
You may want to read about geometrized units. Indeed, in this system Newton's universal gravitational constant ##G = 1##.Roady said:This is funny. 40's something female in my engineering class make humorous state, something about this unit conversion made G sub c(gravitational constant)=1. I never got the chance to explain it is a constant and nothing is going to change it. She left the engineering field for Journalism. Ya'll can rest easy. Above error.
Roady said:Units of BTU, ton's of chillwater, lb mass of steam, are in common use today. I doubt they changed units on Apollo missions to ease calculations, because current crop of engineers were trained in them.
Chestermiller said:1 lbf is the force needed to give a mass of 1 lbm an acceleration of 32.2 ft/sec^2
Which is illegal if you're using the scale for commerce. Buyers would benefit, but sellers would lose money. An unsatisfactory arrangement.Gordianus said:If the spring scale was calibrated with the factor 32.2 in mind, it would read less than 1 pound of force
No. The 32.2 is fixed. And the measured force at the equator would be < 1 lb.Herman Trivilino said:What if you're near the equator where the free fall acceleration is less than 32.1 ft/s2?
If you set an object with a mass of one pound on a spring scale, don't you want it to exert one pound of force on the scale?
The standard way to calibrate a spring scale (including scales that use load cells) involves standard reference masses.Herman Trivilino said:What if you're near the equator where the free fall acceleration is less than 32.1 ft/s2?
If you set an object with a mass of one pound on a spring scale, don't you want it to exert one pound of force on the scale?
Any reputable company would calibrate the scale so that it reads one pound.Chestermiller said:No. The 32.2 is fixed. And the measured force at the equator would be < 1 lb.