Weight and Mass

The terms “mass” and “weight” are used interchangeably in ordinary conversation.
For the most part, when comparing mass and weight on Earth—without moving!—the values for mass and weight are the same

No they’re not, they’re in completely different units.

I’m still on this earth and have no plans of going on any inter-planetary travel soon, nor am I religious:

Mass: If you could count up the number of protons, neutrons, and electrons in an object (which you probably can’t), this would be a measure of the mass. The mass is essentially “how much stuff” is in an object. Yes, I know that’s just a partial definition—but it’s good enough for now. Common units for mass are the kilogram and the gram. If you insist on using silly imperial units, the unit for mass is the slug (true).

Weight: There is a gravitational interaction between objects that have mass. If you consider an object interacting with the Earth, this force is called the weight. The unit for weight is the Newton (same as for any other force). OK, fine—the stupid pound is also a unit for weight.

SI units:

Metric units:


The same mass has a different weight in Norway than it does at the equator, though it’s very minimal and for all practical purposes the difference is inconsequential.

Also, scales measure weight and balances measure mass, regardless of what units they give their results in.

Not to mention that the difference between mass and weight is significant for submerged objects.


Is that why overweight people like to float around in pools??

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Yes it would be about a split heir worth per Kg (or KN if you prefer)

PS> I do feel a little lighter here in Norway when I did in Singapore. Now I know why.

For non-scientific purposes, crane ratings and so forth it’s probably better to either just mark in weight units or use ton-force.

From Wikipedia:

A ton-force is one of various units of force defined as the weight of one ton due to standard gravity.[note 1] The precise definition depends on the definition of ton used.

It’s a one-one conversion. No need to convert to/from kN.

Then the question is; what type of tons? (Metric, Short, Long or MN)
The most relevant for Americans would probably be; Tfr. (Metric) to Tfr. (Short)

PS> Lots more conversion to choose from can also be found on this website.

The point is to avoid having to do conversions. If a crane capacity is marked in tons and for some reason there’s a requirement to be marked in force units just stay in the same system.

Just change the marking units from “TONS” to “TONS-FORCE”.

1 metric ton 1 metric ton-force
1 long ton 1 long ton-force
1 short ton 1 short ton-force

and so on…


Only works with Imperical Units with lbm versus lbf and 32.2ft/s^2 acceleration (on earth); same result numberically, but different units between mass and force, as you pointed out. You can convert using the famous Gc(GsubC),where…1kgm/Nm^2 = 32.2ftlbm/lbf^2 = 1ftslug/lbf*s^2 through dimensional analysis. However, there are numberial changes with SI units, 1kg = 9.81N of force which is essentially acceleration. Same cat, different way to skin it. Both systems use earth’s acceleration as the base line, but one system harmonizes with mass (Imperial) with resulting pounds-force, and the other system harmonizes with acceleration (SI) with resulting Newton.

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its the other way around, due to the centifical speed gravity is less at the equator

A mass at the equator weighs approximately 0.3% less than the exact same mass at the poles. I haven’t done the math for Norway vs Singapore but you can if you want.

American maritime tradition is long tons. Short tons are only used on land.

how about sacks, couldnt believe that when on a drilling rig
There’s metric, imperial, and ( Canadian American) coonie

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I haven’t any need to do the math, I just step on the bathroom scales. :laughing:

But if anybody feel the urge to split hairs, I’m now at 62.5N. Singapore is at 1.5N.

Of course, if I travel to North Cape (71.1 N) I’ll be lighter still, while I may go to Lindesnes (58 N) and get heavier by a few grams.
PS> I’ll still be in Norway, though.

BTW; If I go to the UK will it matter, since they still use “Stones” for body weight. (unofficially)

But not in the Oilfields. Crane capacities were given in ST, as was Bollard Pull on tugs and OSVs.(It sounds bigger that way)

PS> They also liked to publish engine power in IHP for the boats.
The joke was that everything was included. (The Stove and the Fridge in the Galley etc.)

Oh yes; “Sacks” as the unit for bulk mud and cement.
Which than had to be converted to Kips for the “Jacking weight per Leg” and “Afloat trim and Stability” calculations, which has to be made before each rig move.(Otherwise the MWS would not sign CofA to commence the operation)

Cranes depend on the crane manufacturer so those may be short tons. I haven’t been on many tugs with an official rated board pull but they were newer and the board pull was in metric tons. All weights and such for stability measure on the supply boats I was on were in long tons since that’s what our ABS approved stability program worked in.

My point being that the US oilfield isn’t completely stuck in the 1970’s…

B&R, McDermott and SantaFe always specified the capacity of the “Big Rig” cranes in Short Tons, with the boom topped up to the max and in “tieback” mode (not revolving) to make it sound more impressive.

Yes US owned towing vessels without BP Test Certificate was common, until NDA as MWS refused to approve their boats for towing operations.

One company then got innovative and produced something they called an “Estimated BP Certificate”, issued by a Naval Architect Company and based on their “calculations” (no formula given). Needless to say, this was turned down as well.