English vs. SI units of mass and weight

In summary, the SI unit for mass is the kg and for force is the Newton, while the English unit for mass is the slug and for force is the pound. The conversion 1 kg = 2.2 lb comes from the fundamental conversion factors of 1 oz = 28.35 grams and 2.54 cm = 1 inch, along with the acceleration of gravity. The American pound (lb) has the same origin as the Newton, which is based on Newton's second law.
  • #1
Moneer81
159
2
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
 
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  • #2
Moneer81 said:
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?
 
  • #3
Moneer81 said:
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.
 

What are the differences between English and SI units of mass and weight?

The main difference between English and SI units of mass and weight is the unit of measurement used. English units use pounds (lb) for mass and pounds-force (lbf) for weight, while SI units use kilograms (kg) for mass and newtons (N) for weight.

Which units are considered more accurate for measuring mass and weight?

SI units are considered more accurate for measuring mass and weight. This is because they are based on the International System of Units, which uses a standardized definition of the kilogram and newton. English units, on the other hand, are based on historical definitions and can vary slightly in their measurements.

What are the advantages of using SI units over English units?

There are several advantages of using SI units over English units. SI units are more widely accepted and used internationally, making them more convenient for global communication and trade. They also have a more logical and consistent system of measurement, which makes conversions between units easier.

Can English and SI units be used interchangeably?

No, English and SI units cannot be used interchangeably. They are two different systems of measurement and using the wrong units can result in incorrect calculations. It is important to use the correct units for each system to ensure accurate and consistent measurements.

Are there any exceptions to using SI units for mass and weight?

Yes, there are a few exceptions to using SI units for mass and weight. In some industries, such as aviation and marine, the pound and pound-force units are still commonly used. However, these industries also often use SI units alongside English units for international compatibility.

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