# Why Newtons?

#### BW338

##### Member
This appears to be a "D":

MarkII

I read somewhere Robert Goddard did enjoy figs while crunching numbers. (Glad it wasn't prunes)

#### MarkH

##### ---
AT puplishes their thrust curves in pounds. Makes for quick thrust /weight calculations

#### Larry Curcio

##### Well-Known Member
OK, here is a question I have been wanting to ask for years. Why are model rocket motor thrust in Newtons instead of pound?

I have never understood this.

Andrew From Texas

You can get 'em both ways. Why do you believe they should be in pounds instead of Newtons?

Fact is, it ain't the units themselves that makes the metric system superior to the English system (and it is). It's the *consistency* of the units. Using the English system for science and engineering is like doing the caculations in pounds shillings and pence.

#### Ironnerd88

##### Well-Known Member
Fact is, it ain't the units themselves that makes the metric system superior to the English system (and it is). It's the *consistency* of the units. Using the English system for science and engineering is like doing the caculations in pounds shillings and pence.

While I agree that in theory, the metric system is superior, I also think it kinda sucks... And here is why

Nautical Miles. A minute of arc of latitude which can actually be used for navigation over long distances (more than across town). If everything in the metric system had been based upon the nautical mile, I would like it a lot more. Of course this would make a Nautical meter 1.8 regular meters (which turns out to be about 6 feet... not too bad). Or if they had split the Nautical Mile into 2km, a Nautical meter would be about 3 feet...and we could actually use the Km for navigation without throwing the world into chaos.

Just my \$0.02 - off for coffee and a snickers bar

#### MarkII

##### Well-Known Member
While I agree that in theory, the metric system is superior, I also think it kinda sucks... And here is why

Nautical Miles. A minute of arc of latitude which can actually be used for navigation over long distances (more than across town). If everything in the metric system had been based upon the nautical mile, I would like it a lot more. Of course this would make a Nautical meter 1.8 regular meters (which turns out to be about 6 feet... not too bad). Or if they had split the Nautical Mile into 2km, a Nautical meter would be about 3 feet...and we could actually use the Km for navigation without throwing the world into chaos.

Just my \$0.02 - off for coffee and a snickers bar
Well, for distance, I kinda like the attoparsec, the microfortnight and the light-nanosecond.

• One attoparsec per microfortnight is very close to one inch per second.
• One light-nanosecond is approximately 30 centimeters or one foot.
• One light-picosecond, on the other hand, is approximately the width of a speck of ground black pepper, or approx. 362,869 Å.
But if you want to talk about nautical miles, then:

• One light-fortnight is approximately 195 gigaNM.
A standard black powder A, B, C motor is 60 light-picoseconds in diameter.

MarkII

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#### Ironnerd88

##### Well-Known Member
Well, for distance, I kinda like the attoparsec, the microfortnight and the light-nanosecond.

• One attoparsec per microfortnight is very close to one inch per second.
• One light-nanosecond is approximately 30 centimeters or one foot.
• One light-picosecond, on the other hand, is approximately the width of a speck of ground black pepper, or approx. 362,869 Å.
But if you want to talk about nautical miles, then:

• One light-fortnight is approximately 195 gigaNM.
A standard black powder A, B, C motor is 60 light-picoseconds in diameter.

MarkII

LOL!!!! THAT IS EXCELLENT!
I fully support this syetem!

#### MarkII

##### Well-Known Member
A light-picosecond is the distance that light will travel in a vacuum in one picosecond. It is analogous to the more familiar light-year used in astronomy. A picosecond is 1 second x 10^12, or one-trillionth of a second.

1 light-picosecond = 0.3mm, approximately.

• a Quest MicromaxxII-1 motor is 20 light-picoseconds in diameter.
• an Estes mini motor is 43.33333333334 light-picoseconds in diameter.
• a standard Estes or Quest black powder motor in the 1/2A to C range of impulse is 60 light-picoseconds in diameter.
• an Estes D or E motor is 80 light picoseconds in diameter.
• an Aerotech Econoline motor is 96.6666666667 light-picoseconds in diameter.
• a CTI Pro38 motor is 126.666666666667 light-picoseconds in diameter.
and so on.

MarkII (I am 5,842 light-picoseconds in height, on average, when I am at rest. When I am accelerated to somewhere near the speed of light, I am somewhat taller. )

##### Well-Known Member
Newer chemistry books don't even acknowledge the fact the American system exists. Converting to metric really wouldn't be too hard. The problem is that in the end, we were given a choice. The fact they put both metric and American measurements on a box of cereal doesn't help. The answer is just do it.

After all, you pick up a liter or 2 liter bottle of Dr. Pepper when you shop. Not a 1.06 or 2.12 quart bottle (they uses ounces on the bottle).

#### BobH48

##### Well-Known Member
This appears to be a "D":

MarkII

Looks more like an Estes "E" to me.

#### texas-bill

##### Member
If the metric system is so spectacular, why are all these numbers so...un-round?
Avogadro's number = 6.0221415 × 10^23

Planck's constant = 6.626068 × 10^-34 m^2 kg / s

1 coulomb = 6.242×10^18 e

1 g = 9.81 m/s^2

pi = 3.1415926535

Boltzmann's constant k = 1.3806504 × 10^&#8722;23 J/K

permittivity of free space &#949;0 &#8776; 8.854 187 817 × 10^&#8722;12 F/m

permeability of free space &#956;0 = 4*pi x 10^-7

The point is that when doing science or engineering, lots of ugly numbers must be dealt with, and converting between feet and meters or liters and cubic inches is just another trivial step in the process.

The simplifications introduced by the metric system quickly fizz out when the going gets deep. Having to roll your sleeves up and get dirty with the math is unavoidable in spite of the metric system.

.

#### Larry Curcio

##### Well-Known Member
While I agree that in theory, the metric system is superior, I also think it kinda sucks... And here is why

Nautical Miles. A minute of arc of latitude which can actually be used for navigation over long distances (more than across town). If everything in the metric system had been based upon the nautical mile, I would like it a lot more. Of course this would make a Nautical meter 1.8 regular meters (which turns out to be about 6 feet... not too bad). Or if they had split the Nautical Mile into 2km, a Nautical meter would be about 3 feet...and we could actually use the Km for navigation without throwing the world into chaos.

Just my \$0.02 - off for coffee and a snickers bar

I'm afraid you picked up on exactly the point I noted I wasn't arguing. The units themselves have nothing to do with it. What divides what has nothing to do with it.

Consider, say, specific impulse. This is an engineering statistic. It allows for back-of-the-envelope design decisions. Where air breathing engines are concerned, its very rich. Where rockets are concerned, it illustrates the awkwardness of the English system.

Isp was originally impulse divided by propellant weight. (Yes, weight.) When everything was cancelled, you got units of seconds, which did not make a whole lotta sense. It also did not make a whole lotta sense to have force in the denominator.

To be politically correct, the definition of Isp was changed to have mass in the denominator. In the metric system, this yields units of velocity. It is, in fact, effective exhaust velocity. That is

Impulse/Mass has units of
Force*Time/Mass

= (Mass*Distance/Time^2)*Time/Mass

= Distance/Time = Velocity

Because the English-unit engineers did not want to redefine the numerical value of Isp, the unit of mass would have to be the amount of mass that weighs one pound at sea level: the pound(mass). The problem is that impulse in the numerator has, implicitly, another unit of mass: the slug. That means that you cannot cancel the mass in the denominator with the mass in the numerator. You now have units of

Pounds(force) Seconds per Pound(Mass)

You cannot cancel because the units are not *consistent* - my point before, so that you cannot suspect that you were talking about a velocity all along. Note that the pound(mass) is a very nice unit. It makes sense. The problem is that there are no compatible units in the English system  and yet it is still used. This is just one example (out of many) of pounds shillings and pence. The metric system doesn't have this problem. That is why it is superior for physical calculations  objectively.

I want to be clear on the following point: I favor the metric system because the English system is soooo much harder, I lack the ability to use it for physical computations  and this despite the fact that I think very naturally in terms of feet and pounds. Im nowhere near bright enough to pull it off.

I manage to squeeze by with the metric system, because it is actually much easier. The metric system is easier for physical computations because that is what it was designed for. The English system evolved before the physical side of things was understood.

#### MarkII

##### Well-Known Member
Looks more like an Estes "E" to me.
Oops, you're right. 30 Newtons is indeed an E.

MarkII

#### MarkII

##### Well-Known Member
If the metric system is so spectacular, why are all these numbers so...un-round?

The point is that when doing science or engineering, lots of ugly numbers must be dealt with, and converting between feet and meters or liters and cubic inches is just another trivial step in the process.

The simplifications introduced by the metric system quickly fizz out when the going gets deep. Having to roll your sleeves up and get dirty with the math is unavoidable in spite of the metric system.

.
The metric system was not invented to make it possible to express ALL measurements as whole numbers. No measurement system can do that. It was created as a decimalized system of measurement, in which basic units related to each other by powers of 10. It was also created to provide a standardized system, one in which the same unit meant the same thing wherever the system was used. Prior to that, units of measurement such as a "pound" meant different things in different countries and even in different regions of the same country. Criticizing the metric system because it doesn't make all measurements of natural phenomena into nice round numbers is to criticize nature itself for not being organized into "perfect" or "ideal" ratios. Aristotelian notions of nature and cosmology died out long ago. The metric system was never conceived of as an attempt to resurrect them.

MarkII

#### andytherocketeer

##### Well-Known Member
If the metric system is so spectacular, why are all these numbers so...un-round?
pi = 3.1415926535

Dunno. What's Pi in "English"?

(No Idea why people call it English any more - we've been using metric since the 70's-80's, except for pints of beer and miles for road distance)

#### luke strawwalker

##### Well-Known Member
The metric system was not invented to make it possible to express ALL measurements as whole numbers. No measurement system can do that. It was created as a decimalized system of measurement, in which basic units related to each other by powers of 10. It was also created to provide a standardized system, one in which the same unit meant the same thing wherever the system was used. Prior to that, units of measurement such as a "pound" meant different things in different countries and even in different regions of the same country. Criticizing the metric system because it doesn't make all measurements of natural phenomena into nice round numbers is to criticize nature itself for not being organized into "perfect" or "ideal" ratios. Aristotelian notions of nature and cosmology died out long ago. The metric system was never conceived of as an attempt to resurrect them.

MarkII

Yes, exactly...

That's the ONLY thing about metric that I like... changing units or divisions thereof is merely a matter of moving decimal places, which is MUCH easier than correcting the 'proportions' of English units... There is nothing intrinsically 'wrong' with English units when you're a mechanic-- I'm quite accustomed to using a micrometer in the shop, say measuring a crankshaft, which say ends up with a journal diameter of say 2.123 inches, and looking up the spec to find out if it's in tolerance or not, say between 2.130-1.120 inches... SO much easier than when I do carpentry or welding/metalwork and try to add 12 1/4 inches, 5 1/2 inches, and 17 5/16 inches to come up with the next length of material I need to cut. If you're doing metalwork and get down into having to measure in 32nds of an inch or 64ths of an inch, it gets especially rediculous. THAT is where a decimal based system really shines...

If you have to start transposing units, say from inches to feet, THAT is where metric is REALLY nice... no nonsense about having to remember how many inches per this or that, or ounces per gallon, or ounces per cup, or ounces per pound, or whatever... simply move the decimal the right number of places and you're done.

Ya know, it's funny as to what we 'relate' to... when I had a girlfriend up in New Jersey, whenever we'd talk about going someplace or her family would talk about going here or there, they ALWAYS expressed everything as "oh, that's 15 minutes away", or "oh, that's 45 minutes away"... which to us Texans just sounded silly... I didn't get why until I started driving around up there... I'm used to thinking in terms of miles-- I'm 5 miles outside of town, it's 13 miles to the next 'major' town, 40 miles from Houston, 90 miles to our other farm, etc... The idea of 'minutes' to the destination was as foriegn as kilometers... When I started driving around up there, I realized that yeah, something might only be 8 miles away on the map but by the time you took into account all the curves, rises, dips, hills, hollows, traffic, and such, yeah, it took you 15 minutes to get there... and some places that might only be 10-15 miles IN THE OTHER DIRECTION might actually take you 45 minutes or more to get to because of traffic or the roads... let alone when it was icy or snowy...

So, it's kinda funny how regionalized things like that can be... sorta like accents-- they are fading as the world grows smaller but they're still around (for now)...

Later! OL JR

#### Micromeister

##### Micro Craftman/ClusterNut
TRF Supporter
Pi in Engish is the same with decimals as well 3.141592653589732... you forgot the ... "infinity" Andy

It's just as easy to use english decimals units with your woodworking projects as anything else. 12-1/4" becomes 12.25", 5-1/2" to 5.50", and 17-5/16" to 17.3125" add em up 35.0625" or 35-1/16". You'd have the same quandary with 12-1/4mm 5-1/2cm and .438m. It's simply a matter of what we get used to.

That business about converting one thing to another is pure Horse patuties!
With the metric system we still have liters, meters, Kilograms, Newtons, etc to convert from linear to liquid to mass. It's all about the same simply based on 10's instead of 12's. And then there is TIME: Hours, minutes, seconds and so on....base on 60, where's the metic in that?
Is one superior to the other...Not really, considering for the majority of us measuring to more the 2 decimals is a chore. Personally I'm just fine measuring with mico's & calipers to 4 or 5 decimals but for most people 1/16" (.0625") 1.59mm is small enough.

Some things just won't be the same in the metric system; I can't imagine wanting to read a book titled "36,576 meters under the sea". there just isn't the proper ring LOL

Many of us switch back and forth between the two constantly with only minor inconvenience. I'm sure the next generation will be more metric then English. but I'll be damned if I'm gonna replace a lifetimes collection of english tool collecting with metric stuff. If I don't have it by now it's not going to be purchased. That's why the Metric System hasn't really taken over completely....it'll gradually happening with time.

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##### Well-Known Member
It's just as easy to use english decimals units with your woodworking projects as anything else. 12-1/4" becomes 12.25", 5-1/2" to 5.50", and 17-5/16" to 17.3125" add em up 35.0625" or 35-1/16". You'd have the same quandary with 12-1/4mm 5-1/2cm and .438m. It's simply a matter of what we get used to.
Now try writing 3-1/9 exactly in decimal. When you've done that, try 4-3/7.

With the metric system we still have liters, meters, Kilograms, Newtons, etc to convert from linear to liquid to mass. It's all about the same simply based on 10's instead of 12's.
And there's the problem with Imperial measurements. If it were all base 12, it would be fine. Unfortunately there are bases 16, 14, 20, and others, and that's just for units of mass. To complicate matters more, the US devised its own versions of some units. By comparison, metric goes in powers of 10 all the way, and 1 metre is the same in every country on Earth.

And then there is TIME: Hours, minutes, seconds and so on....base on 60, where's the metic in that?
Again, it's not the base but the variety of bases - 60, 24, 7, 28/30/31, 365 and a bit... 60 is actually a very useful number because it divides equally into 2, 3, 4 or 5. 12 is almost as good, being evenly divisible by 2, 3 or 4, which is probably why there are 12 inches to a foot.

Incidentally, here's a little party trick. Ask someone how far they can count on one hand. Chances are they'll get as far as 5. Use your thumb to point in turn to the lower, middle and top parts of the little finger; repeat for ring, middle and index fingers; and thus count to 12 on one hand. Which is how people a few centuries ago did count - at least, those who could count.

Then pretend you're a computer and count digitally up to 31.

##### Well-Known Member
(No Idea why people call it English any more - we've been using metric since the 70's-80's, except for pints of beer and miles for road distance)

Well,we're not going to take credit (blame) for it - even though we use some of our own versions of Imperial measurements! Much of it originated in England so we blame something we don't like on someone else. We like the Metric system so we don't call it the French System.:roll:

##### Well-Known Member
Now try writing 3-1/9 exactly in decimal. When you've done that, try 4-3/7.

My shop teacher of 40+ years ago would tell you that such a measurement doesn't exist - if you cant find it on a standard ruler you can't use it as a construction measure. ( I once turned in a blueprint with 1/3 of an inch and got a long lecture on this)
.

#### Larry Curcio

##### Well-Known Member
Much of it originated in England so we blame something we don't like on someone else.:

Take the Watt, for example. This is a metric unit of power named in honor of the Scottish Engineer, James Watt. It was introduced to replace the previous unit, the horsepower.

The horsepower was invented, of course, by James Watt.

Despite the irony, I still like the metric mindset better. The Imperial mindset will use any unit and divide it by any other unit. Heck! They don't even care if one of the units is metric!

Case in point, another English unit of power is BTU/hour. American air conditioners are calibrated in these terms. American electricity, OTOH, is normally calibrated in watts, so the amount of power consumed is measured in these terms. (Technically a watt is an output measurement, and it is... to the power company, so everyone else uses it as an input measure. But... I digress.)

So the manufacturers of American AC units wanted a measure of efficiency. They could have used watts output over watts input. They could have used BTU's per hour output over BTU's per hour input. They would have got the same number either way. It would have been a dimensionless number between 0 and 1. The closer to 1 it is, the better the efficiency. They could have multiplied it by 100. Closer to 100 the better, right? They wouldn't have even had to explain it. Any damn fool could have understood it!

No. They had BTU's per hour output over watts input. The result is BTU's per watt, and there is no intuitive range to it at all, an' this damn fool don' understannit!

-LarryC

P.S. For those who don't like the value of pi, you don't really need it. Compute the area of a circle as follows

#### Micromeister

##### Micro Craftman/ClusterNut
TRF Supporter
My shop teacher of 40+ years ago would tell you that such a measurement doesn't exist - if you cant find it on a standard ruler you can't use it as a construction measure. ( I once turned in a blueprint with 1/3 of an inch and got a long lecture on this)
.

Non-sense fractions like that just don't come up. Only one who can't or hasn't used a rule or ruler would come up with such sillyness. Our English units can go down to the .000001" but who's going to read them. the very best instruments only read to .0001" and they are a strain to read and maintain.

Adrian: Why is it Europeans believe everything has to be based on one thing or another?
As mentioned earlier, many over here switch back and forth between systems, scales and the like without any problem whatever. For the most part we're not going to change anything anyway so you can measure in 10's if you like and we'll continue do frustrate you all just the way we do until the next couple generations of Americans phase out the Old English System. It's my understanding it took England over a 100-120 years to change why should we think it'll take any less over here. Good grief at least our money system started out in 10's.:gavel::2:

To really answer the original question. The very second post had it correct, Our darn fool Government decided to change our system.... and the people said...Screw you...NO! Why? MONEY...all the existing tooling, measuring, equipment, not to mention changing every container... Mark-II Until a decade or so ago EVERYTHING was imperial. Quarts of milk, Gallons, half Gallons, pints, and half pints of Ice Cream, soda and so on. Sure now the manufacturers have switched over to liters, but I still have a couple Quart bottles I hold on to just to show. It wasn't that long ago ya got a real gallon for the price.

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#### bobkrech

##### Well-Known Member
Looks more like an Estes "E" to me.

Oops, you're right. 30 Newtons is indeed an E.

MarkII
Actually 30 fignewtons is a measure of thrust (a force) and not fignewton-seconds, a measure of the total impulse which is the product of thrust x burn time.

Since the total impulse is actually the product of the number of fignewtons x the consumption time in seconds, we have the classical Newtonian paradox. The slower you consume the 30 fignewtons the greater the total impulse you obtain which as we all know is the reason why your mother told you to eat slowly and why we gain weight as we grow older.

P.S. The speed of light, c = 1.8 terafurlongs per fortnight.

Bob

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##### Well-Known Member
P.S. For those who don't like the value of pi, you don't really need it. Compute the area of a circle as follows

I use 22/7 - if it was good enough for Archimedes it's good enough for me

#### MarkII

##### Well-Known Member
Actually 30 fignewtons is a measure of thrust (a force) and not fignewton-seconds, a measure of the total impulse which is the product of thrust x burn time.
Touché. I knew that, but I misspoke.

Since the total impulse is actually the product of the number of fignewtons x the consumption time in seconds, we have the classical Newtonian paradox. The slower you consume the 30 fignewtons the greater the total impulse you obtain which as we all know is the reason why your mother told you to eat slowly and why we gain weight as we grow older.

Yes, and the more accurately you measure the coastline of Great Britain, the longer it gets. This page has been intentionally left blank.

P.S. The speed of light, c = 1.8 terafurlongs per fortnight.

Bob
What is it in Beard-seconds?

MarkII

#### MarkII

##### Well-Known Member
My shop teacher of 40+ years ago would tell you that such a measurement doesn't exist - if you cant find it on a standard ruler you can't use it as a construction measure. ( I once turned in a blueprint with 1/3 of an inch and got a long lecture on this)
.
I have an engineering scale that contains inch scales divided into 10, 20, 30, 40, 50 and 60. When I need a measurement of say, 7/50 of an inch, I just pull out that scale. One-third of an inch is no problem; it is 10 ticks on the 1/30 scale.

Shop teachers really need to talk to their colleagues who are teaching the Drafting classes.

There is nothing automatic or natural about dividing the inch into eighths, sixteenths, thirty-seconds or sixty-fourths. Those are all arbitrary. As are all measurement systems, Imperial, metric, medieval, or whatever.

MarkII

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#### MarkII

##### Well-Known Member
BTW, one of the earliest proponents of the metric system, who advocated for it for many years prior to its formal creation, was an American, Benjamin Franklin. Metrification is as American as baseball, apple pie, the Liberty Bell and Super Bowl Sunday.

MarkII

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##### Well-Known Member
I have an engineering scale that contains inch scales divided into 10, 20, 30, 40, 50 and 60. When I need a measurement of say, 7/50 of an inch, I just pull out that scale. One-third of an inch is no problem; it is 10 ticks on the 1/30 scale.

MarkII
My teachers comment was that you could figure 1/3" in the class room but the carpenter on the job site would be using a standard ruler or tape measure. Still I would have loved to have had that scale to show him and maybe shut him up - or gotten a longer lecture.

#### MarkII

##### Well-Known Member
My teachers comment was that you could figure 1/3" in the class room but the carpenter on the job site would be using a standard ruler or tape measure. Still I would have loved to have had that scale to show him and maybe shut him up - or gotten a longer lecture.
The set of tools that the carpenter brings to the job site is arbitrary and not set in stone. He can just as easily bring an engineering scale, if that is what is required for the job. It is the carpenter's responsibility to bring the tools that are needed to complete the job. If the blueprints require that a certain section be sawed in half, and the carpenter doesn't happen to have a saw on hand, is that the architect's fault? I wonder how quickly you would have been sent to the principal's office if you had given your shop teacher that response.

MarkII

##### Well-Known Member
The set of tools that the carpenter brings to the job site is arbitrary and not set in stone. He can just as easily bring an engineering scale, if that is what is required for the job. It is the carpenter's responsibility to bring the tools that are needed to complete the job.

MarkII

I have to disagree with that - there are industry standards. American industry recognizes SAE fractions, and often decimal inches and Metric, but the scale you gave it not typically used. And it is the responsibility of the Engineer/ Architect/Draftsman to know what the industry uses. In one of my previous jobs it was not unknown to return a spec sheet or blueprint to our own engineers and tell them "put this in Armstrong terms"

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