12ft.lb ... or ... 12 fpe ?

[Gareth W-B]

Potential energy in the weight. Or the penguin.

Lol.

[deejayuu]

Potential energy in the weight. Or the penguin.

Luv it

[GPConway]

Imagine a spanner on a nut and a weight on the spanner tending to either do it up or undo it (it makes no difference) but insufficient to turn the nut. There is a continuously applied and measurable torque on the nut but nothing is moving - where now is the energy?

Elastic deformation of the spanner, nut and threads and a little heat.
When you take the load off the spanner (reducing the torque) then some of the elastic energy is recovered - the spanner, nut and threads hopefully regaining their former shape. The heat, of course, gets lost to the environment.

George

[rancidtom]

Torque is a force (turning force to be precise). It is expressed by force vector (straight line) applied at 90 degrees to a radius that the force is applied from the centre of rotation. If applied to a static object it remains a force. You can think of it as potential energy. It doesn't really matter if you express it as LbFt or FtLb it means the same. There is no "." required after Lb or Ft as they are accepted abbreviations of imperial units without a full stop. If using ISO units then NM (also Joule or J if we are talking about work done rather than torque applied) is the preferred standard expression but KgM also acceptable as are KgCM NCm etc.
When a force moves an object it does work, it is now considered as energy. FtLb is still the preferred imperial unit as would be NM in ISO units.
When work is done for an amount of time it is then expressed as power. FtLb/sec is one way, 550 of which equal 1 HP (horse power). The ISO expression is Watt, 1 W = 1 Joule/sec = 1 NM/s, 745 of which are approximately 1HP.
It is wrong to express the "power" of a gun - it is the energy of the projectile whether you use LbFt, FtLb, Nm or Joules.
Are all penguins called Joules? Or is that just the ones who apply a Newton of force moving an object a metre against gravity?

[Shedder]

They are both correct and ' wrong ' at the same time as the they are not SI units. To be strictly correct the muzzle energy of a gun should really be expressed in joules, one J being when a force of one newton acts over one meter of distance in the direction of motion of the object/projectile.

A.G

Why is the use of Joules any more correct than foot pounds force just because it is an SI unit? Is a metre any more correct or strictly correct than a yard?

[ChrisC]

All i know is that if you open an airgun all the airgun pixies and fairies escape and can be buggers to catch and get back in again. I've found sandwiches an effective bait to lure them back, in fact that's what FPS stands for.

Fairies+Pixies+Sandwiches

[gc93]

Morning all. Since a similar thread on here many many moons ago (which I simply can not now find) which pre-dated my BBS Mod life iirc (so that makes it at least pre 2008), from which I learned twelve feet per pound should be written 12ft.lb, I have always written it that way.

Of late, however, both on here and another forum I visit, I've started to notice people writing twelve feet per pound as 12 fpe, so is this also a correct notation, is it the new accepted notation that dinosaurs like me should now adopt and replace the former with, or is the former still the one and only correct notation, or, err, should I get a grip as it doesn't really matter?

dinosaurs .. what came before them ? as im still quoting the old yellow pages page number !!??

[lensman57]

Why is the use of Joules any more correct than foot pounds force just because it is an SI unit? Is a metre any more correct or strictly correct than a yard?

It is not the point of being ' correct ' or not. SI units were devised so engineers all over the world would be able to understand each other. Prior to SI units every nation had their own set of nonmenculture/units for denoting weights, energy, , force, length etc. So when we were in uni even as far back as the 1970s SI units were used for engineering terms. I remember that I had an old A Level physics book that I had inherited from my cousin who sat his A levels in the late early 70s. Some of the Imperial units units such as BTU were a real pain to convert into SI.
Although a person outside of the US/Uk would understand ft.lbs to be a unit of energy they may not know exactly how much energy one ft.lbs represents. As with joules the definition is clear, energy/work of one newton of force acting upon an object over a distance of one meter in the direction of its motion.

A.G

[Rich]

But the BTU was quite simple; the amount of heat required to raise the temperature of one pound of water by one Fahrenheit degree.

In transition to metrication we had CHUs, Centigrade Heat Units, still using pounds of water but Centigrade degrees.

3,412 BTU/hr made one kilowatt. 16 ounces made a pound but if they were fluid ounces you needed 20 to make a pint. A pint of water is a pound and a quarter. But not in America. Their gallons were smaller than ours, in the ratio 5/6. Odd, that something in the US was actually smaller than in the UK, but I think it is because the same volume of water works out a bigger number in the states so it sounds larger.

Sorry for the digression.

[rancidtom]

But the BTU was quite simple; the amount of heat required to raise the temperature of one pound of water by one Fahrenheit degree.

In transition to metrication we had CHUs, Centigrade Heat Units, still using pounds of water but Centigrade degrees.

3,412 BTU/hr made one kilowatt. 16 ounces made a pound but if they were fluid ounces you needed 20 to make a pint. A pint of water is a pound and a quarter. But not in America. Their gallons were smaller than ours, in the ratio 5/6. Odd, that something in the US was actually smaller than in the UK, but I think it is because the same volume of water works out a bigger number in the states so it sounds larger.

Sorry for the digression.

US fluid ounces are the same as imperial but the US insists on there being 16 ounces in a pint, therefore a pint of water weighs a pound and a US gallon of water weighs 8 pounds rather than our 20 ounce UK pints and ten pound UK gallons.

[Rich]

Not quite. The US gallon is 0.832 of an Imperial gallon, not 0.8. It's close to a 5/6 ratio, not a 4/5 ratio which is what one would have expected.

[rancidtom]

OK so the US has slightly different ounces or fluid ounces to the UK imperial measures. Quite probably due to their gravity being US gravity rather than UK gravity

[Gareth W-B]

OK so the US has slightly different ounces or fluid ounces to the UK imperial measures. Quite probably due to their gravity being US gravity rather than UK gravity

Yep, that'll be it -- and because American gravity is obviously more prolific in force than ours, that'll explain why so many Americans are significantly wider in girth than the average , coz they have all that extra pressure squidging them down, ergo forcing their mass out sideways (lol), no?

Mind you, said American gravity must be bridging the Atlantic in ever-growing magnitude, however, as any trip to any Aldi or ASDA will confirm to you that we are definitely no longer purely a nation of would-be Twiggies ???

[lensman57]

But the BTU was quite simple; the amount of heat required to raise the temperature of one pound of water by one Fahrenheit degree.

In transition to metrication we had CHUs, Centigrade Heat Units, still using pounds of water but Centigrade degrees.

3,412 BTU/hr made one kilowatt. 16 ounces made a pound but if they were fluid ounces you needed 20 to make a pint. A pint of water is a pound and a quarter. But not in America. Their gallons were smaller than ours, in the ratio 5/6. Odd, that something in the US was actually smaller than in the UK, but I think it is because the same volume of water works out a bigger number in the states so it sounds larger.

Sorry for the digression.

No need. I understand perfectly. My sentiments exactly.

A.G

[Turnup]

Elastic deformation of the spanner, nut and threads and a little heat.
When you take the load off the spanner (reducing the torque) then some of the elastic energy is recovered - the spanner, nut and threads hopefully regaining their former shape. The heat, of course, gets lost to the environment.

George

Not buying that. The energy required to make the deformations you describe can be quantified by the movement of the weight as the load is apple to the spanner = the integral of force times distance. There is still a torque on the whole system and by an the earlier post that is energy - but I can't see where it is while the system is stationery.