51. The International System of Units, or SI units, (which is actually short for "Système International d'Unités") is a very widely accepted system for units of physical quantities. What is the SI unit of the physical quantity "weight"?
From Quiz A Science Mixture
Answer:
Newton
A very common misconception among people is that 'weight' and 'mass' are one and the same thing. This is, however, not true! When we ask somebody what their "weight" is, we usually expect an answer in either pounds or kilograms. What we mean, however, is to ask what their *mass* is, not their weight, without knowing it! By convention, however, we now accept weight and mass to be "the same" quantities. 'Kilogram' is the SI unit of mass, and so it's not that my "weight" is 50 kilograms, but that my *mass* is 50 kilograms.
HOWEVER -- there is a big difference between the two, While mass is defined as "the amount of matter contained in a body", weight is "the product of the mass of the body and the acceleration do to gravity", and is actually a type of force! The acceleration due to gravity varies, depending on where in the universe you happen to be, but on earth it is equal to approximately 10 m/s^2. And so on the earth, a body of mass 50 kilograms would "weigh":
50 kg * 10 m/s^2
= 500
And the unit of weight is 'newtons' and so a body of 50 kg "weighs" 500 newtons!
While we all would have the same mass wherever in the universe we are, our weight would change, depending on our location. While my mass will remain 50 kg, wherever in the universe I am in (that is, unless I overdo the junk-food!), but my weight, in newtons would vary. I would, for example, weigh 1/6th of my weight (not mass) on earth, if on the moon.