Newtons

[emjay1707]

If the weight of a girl here was 500N, what would happen to her weight if she were in Australia?

[New Forester]

Where is "here"...?

 

If you mean the UK, she would weigh the same in Oz, but in almost exactly the opposite direction.  Except that the earth would have turned some number of times while she was on the flight, so it might be the same direction after all.

 

It also depends what she eats once she gets to Oz, and how much surfing she does.

[New Forester]

Ansteyg -

 

I think you have it the wrong way round.  Mass is measured in kg, and does not change whether one is standing on the ground, is in orbit or is standing on the moon.

 

Newtons are a measure of force, as you say.  But weight is the force exerted by a body on the ground -- so surely Newtons are indeed the correct unit for that?

 

Finally, I happen to have quite a few close friends who are "girls" of around 500 kg.  However, they are all of the bovine persuasion -- normal for them, but rather a lot for a human!  1 kg is about 9.8 Newtons, so 500 N (in UK or Oz) is around 51 kg, 112 lb or 8 stone.

 

I did read yesterday of an obese man who is 486 kg -- only 14 kg off the half-ton mark.  But the report was dated 21 September, so perhaps he's dead by now.

[dj_ajax]

The girl would still have the same force on the ground in oz because the gravitational force there is (or well should be in theory) exactly the same as it is here.

[Surgeon]

But volume is measured in cm3 and density in Kg (or g)/cm3.  Therefore mass is measured in cm3 x Kg/cm3 =Kg.  I think you should concede defeat on this one ansteyg.

[Surgeon]

The whole point is that things do not "weigh" kilograms. Kilograms are the SI unit of mass.  Weight is a force and is measured in Newtons hence the reason that 1Kg exerts a weight (force) of approximately 9.8 Newtons on Earth but approximately 1.6 Newtons on the moon where the graitational field strength is approximately 1/6th that on the earth. 

The following definitions are from Whelan and Hodgson "Essential principles of physics" Chapter 3 Newton's Laws p37:  "Mass is a scalar quantity that does not vary. It is measured in Kilograms and is a measure of inertia.  It is measured by comparison with a standard mass,  Weight is a vector force measured in Newtons.  It is a measure of the gravitational attraction of a body and is therefore variable.  It can be measured by a calibrated spring balance. " 

Hope this explains it satisfactorily.

 

[helghast]

mass is a measure of the amount of matter per cm3 in the object. it stays the same where ever you are. Density is the amount of matter the object contains. Volume is the size of the object. Weight is gravitational attraction that the bodily mass exerts on the object. it is measured in newtons.

 

 

[New Forester]

Deamo -  you've got mass and density switched.

 

Matter per cm3 is density.  "Matter" is mass, near enough, and cm3 is volume, so it's the amount of mass in a particular volume.

 

The "amount of matter an object contains" is its total mass.

 

The confusion Ansteyg was having is, I think, caused by the fact that in our constant gravitational field (whether Oz or Blighty) the weight of a kg is also constant.  Therefore we take a short cut and read our bathrooom scales in kg rather than N, pretending that kg are a measurement of weight not mass.

 

[Surgeon]

Spot on New Forester, a far more succint explanation than mine!  Has ansteyg conceded yet?! ;-)