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TOPIC: Negative Nose Loads

Negative Nose Loads 3 weeks 2 days ago #460954

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GD485 wrote:
Hi Prof,
Surely a bag sugar can only have a weight of 1Kg if it's on Earth!
As you stated force exerted by earth's mass on the sugar that results in a force of 1Kg can only be on this planet.

No. the bag of sugar can have a weight of 1Kg anywhere it is subjected to an acceleration of 1G along the axis of acceleration. It just so happens that on earth we do experience an acceleration of 1G due to the mass of the Earth, any other body with the same mass as the Earth would produce an attraction or gravity of 1G
GD485 wrote:
If it is elsewhere (or on Earth) it is mass will be 0.981 Newtons. On the moon it weight would equivalent to 600g but still have a mass of 0.981N.

No. Mass is measured in kg, a Newton is a force. And what I actually wrote was
ProfJohnL wrote:
Humans have decided that the acceleration due to earth gravity has a value of 1 and we compare all other gravitational systems to our own. So for example the gravity of the moon is approx 0.6 that of Earths, so your 1kg bag of sugar on earth will only weigh 600gm on the moon, but its Mass is still 1kg
.
GD485 wrote:
Also the bag of sugar needs to be stationary if it has a velocity (not speed) then the mass will gain energy and therefore mass.

No it doesn't gain mass if it moves. In Newtonian physics the mas remains constant, however its velocity will affect its kinetic energy.

The bag of sugar on the surface of the Earth is following a circular path around the axis of the earth, so it maintains its position relative to the centre of the earth which attracts it, but the surface of the earth opposes the attraction with an equal and opposite force, and the resultant force is measured as its weight. But as it is rotating its velocity is constantly changing, thus it is experiencing a constant acceleration towards the centre of the earth.
GD485 wrote:
Also where are you observing the bag of sugar, are you on the same intertial plane.
In making these observations the properties of the sugar is altered by the observation itself? Heisenberg wasn't too sure or was he!!!
Assuming that gravity is a force but a bloke called Albert postulated that gravity is a distortion of time/space caused by the presence of a massive body. Which came first?

Neither General or Special Relativity changes the physical effects we believe we can practically see or measure.
Unless I use quotes, All advice and opinions given are my own and are given in good faith. Never act on anything you read on a forum unless you can validate and verify its source and content.
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Negative Nose Loads 3 weeks 2 days ago #460955

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ProfJohnL wrote:
GD485 wrote:
Hi Prof,
Surely a bag sugar can only have a weight of 1Kg if it's on Earth!
As you stated force exerted by earth's mass on the sugar that results in a force of 1Kg can only be on this planet.

No. the bag of sugar can have a weight of 1Kg anywhere it is subjected to an acceleration of 1G along the axis of acceleration. It just so happens that on earth we do experience an acceleration of 1G due to the mass of the Earth, any other body with the same mass as the Earth would produce an attraction or gravity of 1G
GD485 wrote:
If it is elsewhere (or on Earth) it is mass will be 0.981 Newtons. On the moon it weight would equivalent to 600g but still have a mass of 0.981N.

No. Mass is measured in kg, a Newton is a force. And what I actually wrote was
ProfJohnL wrote:
Humans have decided that the acceleration due to earth gravity has a value of 1 and we compare all other gravitational systems to our own. So for example the gravity of the moon is approx 0.6 that of Earths, so your 1kg bag of sugar on earth will only weigh 600gm on the moon, but its Mass is still 1kg
.
GD485 wrote:
Also the bag of sugar needs to be stationary if it has a velocity (not speed) then the mass will gain energy and therefore mass.

No it doesn't gain mass if it moves. In Newtonian physics the mas remains constant, however its velocity will affect its kinetic energy.

The bag of sugar on the surface of the Earth is following a circular path around the axis of the earth, so it maintains its position relative to the centre of the earth which attracts it, but the surface of the earth opposes the attraction with an equal and opposite force, and the resultant force is measured as its weight. But as it is rotating its velocity is constantly changing, thus it is experiencing a constant acceleration towards the centre of the earth.
GD485 wrote:
Also where are you observing the bag of sugar, are you on the same intertial plane.
In making these observations the properties of the sugar is altered by the observation itself? Heisenberg wasn't too sure or was he!!!
Assuming that gravity is a force but a bloke called Albert postulated that gravity is a distortion of time/space caused by the presence of a massive body. Which came first?

Neither General or Special Relativity changes the physical effects we believe we can practically see or measure.

Sorry, but your opening statement is incorrect Prof.

Nothing weighs 1KG. Weight is a force, the SI unit of which is Newtons, NOT Kilograms.

A body that has a MASS of 1KG has a mass of 1KG irrespective of the gravitational force to which it is subjected.

On the moon, that same body would be subject to a gravitational force of only 0.16G, but it would still have a mass of 1KG.
Last Edit: 3 weeks 2 days ago by Icaru5.
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Negative Nose Loads 3 weeks 1 day ago #460960

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Icaru5 wrote:
Sorry, but your opening statement is incorrect Prof.

Nothing weighs 1KG. Weight is a force, the SI unit of which is Newtons, NOT Kilograms.

A body that has a MASS of 1KG has a mass of 1KG irrespective of the gravitational force to which it is subjected.

On the moon, that same body would be subject to a gravitational force of only 0.16G, but it would still have a mass of 1KG.

I agree the SI unit of force is the Newton, but Weight is a perfectly legitimate way of expressing the reaction force when a mass is acted on by gravity which is the specific point I was making.

Where I have suggested that a mass of an object would change under different gravitational circumstances. ?

The gravitational attraction on the surface of the moon is approximately 0.6G not as you state 0.16G.
Unless I use quotes, All advice and opinions given are my own and are given in good faith. Never act on anything you read on a forum unless you can validate and verify its source and content.
Last Edit: 3 weeks 1 day ago by ProfJohnL.
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Negative Nose Loads 3 weeks 1 day ago #460961

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Before I hasten up into the loft and retrieve my books by S Timoshenko, or Beer and Johnston, does the recent redefinition of the "kilogram" affect this erudite debate? Studying in the era of mixed units which included "slugs" and "poundals", "Newtons" etc I always had difficulty figuring out the various relationships. Even my wheel bolt torque wrench serves to further confuse me with its mixed units. Perhaps I should take the dogs a walk. :evil:
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Negative Nose Loads 3 weeks 1 day ago #460962

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ProfJohnL wrote:
Icaru5 wrote:
Sorry, but your opening statement is incorrect Prof.

Nothing weighs 1KG. Weight is a force, the SI unit of which is Newtons, NOT Kilograms.

A body that has a MASS of 1KG has a mass of 1KG irrespective of the gravitational force to which it is subjected.

On the moon, that same body would be subject to a gravitational force of only 0.16G, but it would still have a mass of 1KG.

I agree the SI unit of force is the Newton, but Weight is a perfectly legitimate way of expressing the reaction force when a mass is acted on by gravity which is the specific point I was making.

Where I have suggested that a mass of an object would change under different gravitational circumstances. ?

The gravitational attraction on the surface of the moon is approximately 0.6G not as you state 0.16G.

I’m not being drawn into an argument here Prof, as it has happened too many times, on reflection, regrettably, but your opening statement made reference to a condition under which the 1KG would remain.

Regarding your figure for the gravitational force on the moon, I’m afraid it is wrong, and is indeed 0.16G as I correctly said.

If it was 0.6, we would be in serious trouble for many reasons ! - Not least unimaginable tidal forces.
Last Edit: 3 weeks 1 day ago by Icaru5.
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Negative Nose Loads 3 weeks 1 day ago #460980

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In view of the fact that we are all on the same planet where the gravitational forces on the whole vary negligibly, it is fairly irrelevant whether we talk about mass or the gravitational force acting on that same mass. So long as we remain consistent, the relationship between any two values, whether mass or force, will remain constant.
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Negative Nose Loads 3 weeks 1 day ago #460982

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My mistake.

I acknowledge that my reference to the moons gravitational force was wrong. it is 0.166 that of Earths or 1/6th.

Edited addition
All my other references to weight in KG are correct as I referenced them to a gravitational value of 1.

It is a long and accepted tradition that in non scientific circles the force exerted by gravity on a Mass is commonly referred to as weight.
Unless I use quotes, All advice and opinions given are my own and are given in good faith. Never act on anything you read on a forum unless you can validate and verify its source and content.
Last Edit: 3 weeks 22 hours ago by ProfJohnL. Reason: Additional comment
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Negative Nose Loads 3 weeks 17 hours ago #461020

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ProfJohnL wrote:
My mistake.

I acknowledge that my reference to the moons gravitational force was wrong. it is 0.166 that of Earths or 1/6th.

Edited addition
All my other references to weight in KG are correct as I referenced them to a gravitational value of 1.

It is a long and accepted tradition that in non scientific circles the force exerted by gravity on a Mass is commonly referred to as weight.

I entirely agree Prof, and on a Caravan forum, I wouldn’t normally dwell on the difference between mass and weight, but in this case, the OP (Don’t quite remember who it was ! :P ) made a point of distinguishing between the two and it continued on from there !

As is often the case Prof, we have once again found ourselves needlessly debating the same irrelevant point, long after the majority of those more sane than ourselves have disappeared due to lack of interest and rightly so ! :P
Last Edit: 3 weeks 17 hours ago by Icaru5.
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Negative Nose Loads 3 weeks 17 hours ago #461021

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You's should write a book you's two ! ;)
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the round table some day !!
Sorry !!
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Negative Nose Loads 3 weeks 17 hours ago #461022

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Craigyoung wrote:
You's should write a book you's two ! ;)

I’ve no doubt the Prof has already written several Craig, he doesn't need my input !
Last Edit: 3 weeks 17 hours ago by Icaru5.
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