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TOPIC: Negative Nose Loads

Negative Nose Loads 5 months 1 week ago #460802

  • ProfJohnL
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Just returning to Icaru5's hypothetical scenario where the tow car is loaded to 20kg above its GVW limit, but the trailer has a negative nose load which lifts the ball hitch and which will reduce the cars weight when coupled so it weighs less than its GVW limit.

This is actually more interesting than it might at first seem.

If the outfit were weighed, the car would appear to be within its GVW and it might get away with it. But this is where an anomaly might begin to appear.

The EU regulations as drafted by Brussels, refers to vehicle Masses not weights, and this is where the misuse of measurement units that is so common here leads to confusion and in this case legal difficulties.

Scientifically minded readers will know there is a difference between Mass and Weight. They are related but they are not the same thing. All matter has a mass, but it will only demonstrate a weight (which is a force) when it is subjected to an acceleration. In earthly terms we are used to the acceleration caused by gravity to wards the centre of the earth, and we use that as our reference. Scientifically if we have mass of 1kg it will be attracted to the centre of the earth with a force of 1 Kilogram force. (or more accurately 9.81 NM)

Good old Sir Isaac Newton worked it all out and gave us the basic formula of

Force = Mass x Acceleration.

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

The astute roadside tester will know this and should measure the axle loads of the car and caravan as an outfit, and just as the solo car, and armed with that information they can calculate the mass of the car and the caravan and the transfer of loads, and the direction of forces. By doing so they would discover the negaive nose load and the car with its excessve Mass over its MAM.

It also worthy to note that on the VIN plate whilst the what we conventionally call GVW is officially known as Maximum Authorises Mass, but the axles values are Loads not masses. so it is permissible to measure the axle loads by weighing them.
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: 5 months 1 week ago by ProfJohnL. Reason: Added comment
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Negative Nose Loads 5 months 1 week ago #460809

  • EH52ARH
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So if you have a lorry filled with racing pigeons, and it weighs saw 20 tonnes, and they all decided to fly inside the lorry at the same time, how much does it weigh then ??
Hutch
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Sante Fe 2014, tugging a Coachman 560 VIP. 2013.
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Negative Nose Loads 5 months 1 week ago #460810

  • Craigyoung
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EH52ARH wrote:
So if you have a lorry filled with racing pigeons, and it weighs saw 20 tonnes, and they all decided to fly inside the lorry at the same time, how much does it weigh then ??

Trust you !! ;)
Ford Kuga 2.o Tdi & a Sprite Major 6TD

Sir Crying -
Will possibly get to
the round table some day !!
Sorry !!
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Negative Nose Loads 5 months 1 week ago #460818

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EH52ARH wrote:
So if you have a lorry filled with racing pigeons, and it weighs saw 20 tonnes, and they all decided to fly inside the lorry at the same time, how much does it weigh then ??

:evil: It depends ..........

Stop reading now if you are not a geek..... :cheer:

...If its "filled" there won't be any room to fly. so its a mute question :blush: - and where will the driver sit? :S

.......on, if the lorry has free air movement in and out ( which to fly they must be alive and thus able to breath) in which case any difference in the air pressure caused by wing beats will almost certainly be able to escape the lorry and thus not transfer all its thrust to the bed of the lorry so it will weigh less.... But its mass including load will remain the same!!!!

What about the change in inertial load when the pigeons push off to fly and the impact when they land can you quantify that ? How much will it change the pressure in the trucks trailer tyres? :blink:
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: 5 months 1 week ago by ProfJohnL. Reason: Add sillyness
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Negative Nose Loads 5 months 1 week ago #460819

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..... but what's to say they'll all push off together forcing a downward motion and load movement !!! :P
Ford Kuga 2.o Tdi & a Sprite Major 6TD

Sir Crying -
Will possibly get to
the round table some day !!
Sorry !!
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Negative Nose Loads 5 months 6 days ago #460855

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The Prof asked, where does the driver sit, on the drivers seat. Dooh.

Ok Prof how do you get Four elephants into a Citron, 2 CV, ;) Oh two in the front two in the back, :P

PS. Tyre pressures do not change unless the pigeons take of and land enough to raise the tyre temperature. :woohoo:
Hutch
Sir Were-Rabbit
Sante Fe 2014, tugging a Coachman 560 VIP. 2013.
Rural Milton Keynes
Last Edit: 5 months 6 days ago by EH52ARH. Reason: Correction
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Negative Nose Loads 5 months 3 days ago #460947

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Towing is more Brains than horsepower
Last Edit: 5 months 3 days ago by GD485.
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Negative Nose Loads 5 months 3 days ago #460951

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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.
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.
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.
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?

You seem to be getting Mass and Force mixed up a little GD ...

A bag of sugar that has a mass of 1KG has a mass of 1KG, whether it is on Mars, the moon, Venus or elsewhere.

What would differ if the bag of sugar was subject to a different gravitational pull is the force that the 1KG bag of sugar would exert on the ground.

Newton’s second law correctly states that F=M x A, (Force = Mass X Acceleration)

Since ...

The bag of sugar has a mass of 1KG

And, using widely accepted values, for the purposes of calculation,

Acceleration due to gravity on Earth is 9.81M/S/S
And
Acceleration due to gravity on the Moon is 1.62M/S/S

On earth, the bag of sugar exerts a downwards force of 1 x 9.81 = 9.81 Newtons.
On the moon, it exerts a force of 1 x 1.62 = 1.62 Newtons.

However, no matter where the bag of sugar is, it has a mass of 1KG.

To take it a step further, when somebody says their weight is 70KG, that is actually wrong. Their MASS is 70KG.

If they took their bathroom scales to the moon, and stood on them, the scales would read 11.56KG (70 / (9.81/1.62)) and their scales would be wrong. The reason being that everyone’s bathroom scales and other “weighing” equipment is calibrated for use on earth.

Despite being on the Moon, the person’s MASS is still 70KG, but despite displaying kilograms, the scales are not able to measure mass, only force, but because they will (most probably) only ever be used on earth, using M=F/A, they use 9.81 for A as a fairly safe bet to tell you your mass.

Unfortunately, if you want to use your bathroom scales on the Moon, you’ll need to have them (significantly) recalibrated !
Last Edit: 5 months 3 days ago by Icaru5.
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Negative Nose Loads 5 months 3 days ago #460952

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Towing is more Brains than horsepower
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Negative Nose Loads 5 months 3 days ago #460953

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GD485 wrote:
Icaru
The unit kilogram is an alternative way of expressing the force acting on a mass that only occurs on earth. The force of 9.81 N is the force applied to specific mass that earthlings call 1kg
As a planet of smaller mass has a different gravitational force then the unit kg cannot exist
This was what Newton was trying to create, a uniform unit of mass independent of gravity or was gravy:-)

Sorry, but your opening sentence is absolutely not true GD.

The Kilogram is the SI unit of MASS. The SI unit of force is the NEWTON.

Your second sentence makes sense, but to help you with the rest, please read the edited version of my previous post which uses bathroom scales as an example.
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