English vs. SI units of mass and weight


by Moneer81
Tags: english, mass, units, weight
Moneer81
Moneer81 is offline
#1
Sep18-05, 09:26 AM
P: 153
Hi,

We know that the SI unit for mass is the kg, and that for force is the newton, where 1 N = 1 Kg x the acceleration due to gravity.

On the other hand, the English unit for mass is the slug, and that for force is the pound, and again we have a similar relationship based on Newton's second law.

My question is, where does the american pound (lb) come from? and where does the conversion 1 kg = 2.2 lb come from?

Thanks
Phys.Org News Partner Physics news on Phys.org
Physicists design quantum switches which can be activated by single photons
'Dressed' laser aimed at clouds may be key to inducing rain, lightning
Higher-order nonlinear optical processes observed using the SACLA X-ray free-electron laser
yourdadonapogostick
yourdadonapogostick is offline
#2
Sep18-05, 09:51 AM
P: 266
Quote Quote by Moneer81
My question is, where does the american pound (lb) come from?
same place the Newton came from. F=ma===>W=mg, g=32.2ft/s^2


and where does the conversion 1 kg = 2.2 lb come from?
where do any conversions come from?
rbj
rbj is offline
#3
Sep18-05, 11:49 AM
P: 2,265
Quote Quote by Moneer81
Hi,

We know that the SI unit for mass is the kg, and that for force is the newton, where 1 N = 1 Kg x the acceleration due to gravity.
that is actually not the definition of the Newton and it is, in fact, wrong. the Newton is the amount of force needed to accelerate 1 kg at a rate of 1 meter/sec^2. since the acceleration of gravity (on the Earth) is about 9.8 times that, then the amount of force that accelerates a kilogram at that rate is 9.8 N.

On the other hand, the English unit for mass is the slug, and that for force is the pound, and again we have a similar relationship based on Newton's second law.
1 pound of force will accelerate one slug at a rate of 1 ft/sec^2. in civil engineering on this side of the pond (U.S.), rather than talk of the slug, we define a pound mass (lbm) to be the amount of mass that weighs one pound (or exerts one pound force, lbf, onto the ground). so 1 lbf = 1 lbm * 32.174 ft/sec^2.

My question is, where does the american pound (lb) come from? and where does the conversion 1 kg = 2.2 lb come from?
oh geez. that goes back. i don't remember what the most fundamental conversion factor is. i think that 1 oz = 28.35 grams and 2.54 cm = 1 inch. i think those are the most fundamental numbers plus what the acceleration of gravity is.


Register to reply

Related Discussions
[SOLVED] What are the standard units for inertial mass and gravitational mass? Introductory Physics Homework 10
units for weight Introductory Physics Homework 5
atomic mass units Chemistry 1
English System Units and R value Introductory Physics Homework 4
Atomic Mass Units Introductory Physics Homework 3