Lift and stuff.

[old man emu]

2 hours ago, APenNameAndThatA said:

So does that mean that if an RAAus aeroplane has a maximum takeoff weight of 600 kg it has a maximum takeoff mass of about 60 kg? 

Exactly. By George, he's got it! He's really got it!

 

 

Does this affect our calculations? Not really if at the beginning you specify the units you want to work with. If you see the MTOW quoted as 600 kgs, you know that you are going to be talking in units of in the centimetre-gram-second (CGS system) and you are referring to a unit called kilogram-weight which is mass x acceleration due to gravity. If you quote it as 60 kg mass, you are working in the International System of Units (SI) (metre-kilogram second), and ignoring the acceleration due to gravity.

 

Since Mankind began comparing the amount of things by weighing, it has used values that are really a comparison the the force of Gravity. So our cultures have named certain amounts of force as by many names, https://en.wikipedia.org/wiki/List_of_obsolete_units_of_measurement. In every field except the basic sciences, a word that describes the heaviness if something is really relating the force it exerts due to the acceleration due to gravity.

 

The etymology of the word "weigh" is Old English wegan (class V strong verb, past tense wæg, past participle wægon) "find the weight of, measure; have weight; lift, carry, support, sustain, bear; move," from Proto-Germanic *wegan (source also of Old Saxon wegan, Old Frisian wega, Dutch wegen "to weigh;" Old Norse vega, Old High German wegan "to move, carry, weigh;" German wiegen "to weigh," bewegen "to move, stir"), from PIE root *wegh- "to go, move, transport in a vehicle." And "wagon" is from the same source.

 

It's pretty obvious that if you tell a non-physicist that your plane has a mass of 60 kgs, they will imagine that you are flying something like the Gossamer Albatross.

[APenNameAndThatA]

So you are saying that an average light sport aircraft has a mass of about 40 kg? 

[APenNameAndThatA]

OME, are you saying that a litre of water has a weight of 1 kg and a mass of 100 grams? 

[pmccarthy]

This is a silly discussion. I learned in high school that mass is a property of the object and weight is the force it exerts due to the gravitational field it is in. What is hard or confusing about that?

[old man emu]

4 hours ago, APenNameAndThatA said:

So you are saying that an average light sport aircraft has a mass of about 40 kg? 

 

3 hours ago, APenNameAndThatA said:

OME, are you saying that a litre of water has a weight of 1 kg and a mass of 100 grams? 

 

Yes and Yes. 

 

For the last time. "weight" is something that matter has if it is influenced by the gravitational attraction of another bit of matter. We use that word in our day-to-day lives to refer to the resultant force caused by the effect of the gravitational attraction of the Earth. In round figures that resultant force is found by multiplying the amount of mass by approximately 10.

 

Mass is simply the number of atoms that compose the sample of matter. Think of mass as the number of bricks in a wall. 

 

This picture shows a spring scale. The face is divided with marks that indicate how far the the spring has been stretched. The distance stretched is related to the resultant force which is equal to the product of the mass and acceleration due to gravity is applied to the spring. The markings on the scale reflect the use to which the spring scale is to be put.

This scale is used to tell the "weight" of objects. 

 

This scale is used to show the number of Newtons of Force applied to the spring. 

[Thruster88]

So teacher you want us to believe you were using an obsolete system of units all along? Sorry not buying it. If you can prove the a litre of water has a mass of 100grams using any system of measurement I will come back to class.  

 

The CGS system goes back to a proposal in 1832 by the German mathematician Carl Friedrich Gauss to base a system of absolute units on the three fundamental units of length, mass and time.^[4] Gauss chose the units of millimetre, milligram and second.^[5] In 1873, a committee of the British Association for the Advancement of Science, including physicists James Clerk Maxwell and William Thomson recommended the general adoption of centimetre, gram and second as fundamental units, and to express all derived electromagnetic units in these fundamental units, using the prefix "C.G.S. unit of ...".^[6]

The sizes of many CGS units turned out to be inconvenient for practical purposes. For example, many everyday objects are hundreds or thousands of centimetres long, such as humans, rooms and buildings. Thus the CGS system never gained wide general use outside the field of science. Starting in the 1880s, and more significantly by the mid-20th century, CGS was gradually superseded internationally for scientific purposes by the MKS (metre–kilogram–second) system, which in turn developed into the modern SI standard.

Since the international adoption of the MKS standard in the 1940s and the SI standard in the 1960s, the technical use of CGS units has gradually declined worldwide. SI units are predominantly used in engineering applications and physics education, while Gaussian CGS units are commonly used in theoretical physics, describing microscopic systems, relativistic electrodynamics, and astrophysics.^[7][8] CGS units are today no longer accepted by the house styles of most scientific journals,^{[citation needed]} textbook publishers,^{[citation needed]} or standards bodies, although they are commonly used in astronomical journals such as The Astrophysical Journal. The continued usage of CGS units is prevalent in magnetism and related fields because the B and H fields have the same units in free space and there is a lot of potential for confusion when converting published measurements from CGS to MKS.^[9]

The units gram and centimetre remain useful as noncoherent units within the SI system, as with any other prefixed SI units.

[old man emu]

4 hours ago, Thruster88 said:

So teacher you want us to believe you were using an obsolete system of units all along?

Obsolete in the eyes of the SI unit system, but for distance and mass the units are simply 1/1000th of those of the SI system.

 

5 hours ago, Thruster88 said:

If you can prove the a litre of water has a mass of 100grams using any system of measurement I will come back to class.  

Measuring scales that tell us the "weight" of an object are actually scales that tell us the force required to stop the object from falling further towards the Earth. They measure the equal and opposite force to the force of gravity. If their indicator scales were marked in SI units, they would show this force in Newtons.  In 1948, the 9th Conférence Générale des Poids et Mesures (CGPM) Resolution 7 adopted the name Newton for this force. Thus the word "Newton" in this usage is new to the vocabulary. Since it is a new term, it is not likely to displace each language's word for "weight" in the vernacular. So scales continued to be marked with the words kilogram or pound, depending on the local common term.

 

When we talk about the weight of an aircraft, we are talking about the number of Newtons of force it applies to a measuring device. 

[APenNameAndThatA]

It’s really funny knowing every brick but being clueless whether you have a cathedral or a pile of rubble. 

[Thruster88]

OME we are all very aware of the difference between mass and weight. You are claiming the an object here on earth with a weight of 1 kilogram has a mass of only 100g, it is bullshit.

[old man emu]

I can tell you that according to the scientists working in the area of chemistry, one litre of water contains 55.55 mols of water, therefore contains

55.55 x 6.02214076 × 10²³. water molecules ( mols x Avogadro's Number). 

 

In Norse mythology, Gram (Old Norse Gramr, meaning "Wrath") is the sword that Sigurd used to kill the dragon Fafnir. It is primarily used by the Volsungs in the Volsunga Saga. Nowhere in the Volsunga Saga is a clear description of Gram given. And I can't find a satisfactory definition of "gram" in the places I can find a definition of "second" and "metre". Currently the kilogram is defined as 6.62607015 × 10⁻³⁴  joule x second.

 

The joule (symbol: J) is a derived unit of energy in the International System of Units. It is equal to the work done on an object when a force of one newton acts on that object in the direction of the force's motion through a distance of one metre. The units that the joule is derived from are:

As an aside, if you multiply joules by seconds, as the this  6.62607015 × 10⁻³⁴  joule x second says to do them you get kg x velocity, which is momentum.

 

The problem that I have is that the kilogram is being defined by itself.

 

 

 

 

[old man emu]

I fear that this topic has become an Oozlum bird. 

 

It would be churlish of me to use my Moderator's authority to lock this thread, so another moderator might like to. In all good faith I can't see this discussion reaching agreement. The only consensus that I can see is that we agree to disagree. 

 

 

[Jabiru7252]

I think one or two are deliberately antagonizing some others and those others should not take the bait. We all know there are clever folks among our ranks and there's possibly a few dummies. Let's put this to rest now and move on. 🙉

[APenNameAndThatA]

I’ll have one last go at straightening this out. See the spring scale you posted a pic of? 10 N = 1000 g = 1 kg. 

 

F = ma

 

10 = 1 x 10

 

with units 

 

10 N = 1 kg x 10 m/s/s

 

If we look sub in the spring scale, we see 

 

1000g weight = 1 kg weight = 10 N weight = 1 kg mass times 10 m/s/s acceleration due to gravity on Earth. 

 

I am so sad to see this end. The sooner it does, the sooner we can move onto angle of attack meters. 

 

Once again, look at the scale *you* posted. 1 x 10 = 10 N, not 10 kg. 

 

☹️

 

Apart from anything else, can you imagine if there were two meanings of kg that were an order of magnitude apart? There would be so many accidents. And, OME, if you are trolling, you really shouldn’t because some people listen to you. But if you are trolling, you won and gave me a laugh. 

[APenNameAndThatA]

 

And OME, I have a confession. I said I read the link you posted. I didn’t. I lied. Can you let us know your real name in case we meet you one day? I’m Andrew Nielsen. 

 

Edited April 3, 2021 by APenNameAndThatA

[old man emu]

 

50 minutes ago, APenNameAndThatA said:

I said I read the link you posted. I didn’t. I lied

 

And that's been the problem all along. You don't read anything and are able understand it. Then you go and pick the nits out of it and twist them around in order to antagonise. I have been saying that mass refers to the number of molecules, while weight refers to the force that mass would exert if it was accelerated at ~ 10 m/s/s.

 

In introducing those pictures I was illustrating that The markings on the scale reflect the use to which the spring scale is to be put, and I said that plain and clear. A scale marked in kilograms could be found in everyman's fishing tackle box, but a scale marked in newtons is likely only to be found in a physics classroom.

 

There is only one crime that I abhor, and that is lying. I can forgive any other crime from littering to murder, but I can't forgive lying. So if we ever met, face-to-face, the next thing you would see is my back. 

1 hour ago, APenNameAndThatA said:

 The sooner it does, the sooner we can move onto angle of attack meters. 

What's the point, you wouldn't read any part of the discussion to understand what is being said. 

 

1 hour ago, APenNameAndThatA said:

if you are trolling,

I'm not the one sitting under a bridge waiting for the Billy Goats Gruff.

 

[APenNameAndThatA]

I read it in the end, OME. It is best to forgive liars when they confess, otherwise there is no motivation to fess up. 

 

Riddle me this, OME, with the second scale you posted, if you hung a litre of water off the scale, would it show 10 N and 1000 g, or would it show 1 N and 100 g? 

 

Just to be clear, the Shinco scale has newtons on the left and grams on the right. (Newtons and kg seem to be in the Grade 7 curriculum in Australia, so there will be lots of spring scales marked with both.) 

Edited April 3, 2021 by APenNameAndThatA

[Admin]

Enough, we are here to discuss between us good people, not inflame. A Pen Name 2 weeks cooling off

[Jase T]

Is this where I throw in a quantum physics discussion about the fact that gravity does not exist? That its an interpretation of the impact on space/time of a body with a significant mass? Gravity is relative to your frame of reference!!! 

Perhaps the Best Lay explaination  i have ever seen is here.. 

 

 

 

 

 

Edited April 3, 2021 by Jase T

[Peter Piper]

Judging by this thread, old man emu was ruder than APenNameAndThatA, if that is who A Pen name is. 

 

 "aro, I am crying tears of blood. You keep saying that I know f-all about physics. I cry because you know f-nothing." 

 

"Sorry that I didn't jump to reply to your demand for a reply, but I've wasted too much time trying to show someone who has no understanding of the manipulation of algebraic equations and a complete lack of primary school arithmetic ability to know that three divided by ten is the decimal fraction 0.3 .

 

How you are ever going to be able to do the simple calculations required for aerial navigation has me stumped." 

 

Especially when Mr Emu seems to be saying that a litre of water has a mass of 100 g. Maybe Pen Name said something rude and I missed it. Unless the problem was the zinger about the cathedral. I hope I don't get banned for standing up for Mr Pen. I only just got here! Can someone explain what is going on? 

[old man emu]

3 hours ago, Peter Piper said:

Can someone explain what is going on? 

In a number of threads, APenNameAndThatA has been provoking me. You would have to go back through a lot of posts in a number of threads to see all that has been done. I've offered a lot of stuff and links where possible, but instead of making positive contributions or sensible rebuttals he has simply sought to enrage me.

 

I'm sorry that your introduction to this fine and very useful forum has been marred by the antics of one person. Don't think that the standards of the forum are in the gutter. It is a very useful resource and I look forward to your contributions in the future.

[Yenn]

The provocation seems to be by more than one person. Isn’t it time to change the subject.

[old man emu]

Yeah. I think it's been done to death. 

[Admin]

Thread closed