What is the difference between Weight and Mass?

I totally understand what you mean. Its a pretty good question. Mass is an inertial property; that is, the tendency of an object to remain at constant velocity unless acted upon by an external force. Weight is the force created when a mass is acted upon by a gravitational field. Now, you might have heard of that a million times but that is really what it boils down to . So why on Earth do we have the same unit for them both??? Notice I said Earth. It is because in everyday situations, the mass and weight of an object are directly proportional to each other, which usually makes it unproblematic to use the same word for both concepts. The same word and hence the same unit is used in daily life for the sake of convenience, apart from the fact that you cant actually go tell everyone on the planet that the units they used since childhood was all wrong. It is simply not practical.

Ok. I read all of the other answers, and they are all good answers. Yes, the unit of force is the Newton, and yes the unit of mass is the Kilogram. Your weight, as everyone has pointed out, is dependant on both, but generally stated in terms of kilograms. On Earth, the acceleration of gravity (the force) is 9.81m/s^2 On the moon, the acceleration of gravity is less - 1.62 m/s^2 Your weight, being dependant upon this force, would be less on the moon. The ratio is 1 : 6.055555555 I'd like to address the last part of your blurb, there. Weight is measured on a scale, like the one most people have in their bathroom, which are usually spring loaded. Mass, however, is measured on a balance, like the one your doctor probably uses to "weigh" you, at your appointment. The counter-weights are slid back and forth to create more or less leverage at different distances from the pivot, balancing out your body. On the moon, these counter-weights, like your body, would be effected by 1/6 the gravity and would weigh less, just like your body. If you were to use the bathroom scale to measure your weight on the moon, you would find that it reads 1/6 of what your weight is on Earth. If you use the beam balance from the doctor's office to measure your mass on the moon (because this is what it truly measures), you would find that the reading is identical to what it read back on Earth.

because your weight on earth is equal to your mass therefor we use mass and weight as interchangable units of measure on earth

First, the IS unit for weight is Newtons,not kilograms. Second, kilograms is the IS unit for mass. Weight is equal to the mass of the person multiplied by the acceleration due to gravity. The acceleration due to gravity of the earth is approximately 9.8m/s so your weight on earth is your mass multiplied by 9.8m/s. You see, your weight on earth varies with your weight on the moon since the acceleration due to gravity of the moon is different from that of the earth. Acceleration due to gravity in common term is the pull of gravity.

mass is the amount of stuff a thing is made from. kgs Slightly different from density, in that density is the mass within a specific volume. kg/cm³ Weight is the effect of gravity on the thing. and is mesured in kg force. which is different to kgs. however, we just use kg in our ignorance. i.e. the attractive force exerted on the thing by gravity. Gravity is dependant on the mass of the attractive thing. i.e. Earth gravity is approx 9.81 The moon is much less as it has less mass. So you would weigh less on the moon. you could hold a pendulum next to a massive object such as an air craft carrier or some thing and notice a slight swing towards it. Hope that clarifies, but just in case you could always visit wikipedia who already have most of the standard questions here.

mass is a scalar quantity while weight is a vector quantity. weight is the force by which earth attracts a body towards itself (not only earth but everything in the universe attracts other things). weight is mass x g {g=acceleration due to gravity(for earth it is approx 9.8 m/s).} and the correct unit of weight is N (newton i.e. unit of force.) for common use unit of weight is Kgf (kilogram force i.e. 1/10 th of (m * g)) or gf (gram force). on earth 1 kgf = 1 kg.

yes, weight is a function of mass and gravity. so we "should" be using units like newtons, but the reason we don't is because, it everyday use, were not going to be in space, the moon, another planet, etc. and the difference in gravity due to elevation (and density of the mass beneath you) isn't going to make enough difference to matter to 99.9% of you people in the world. Its just simplifing stuff...in chemistry...reaction are "assumed" to occur at STP unless noted otherwise, because it simplifies things... think about it like this...you how understands...would have to explain to my grandfatherhow much cheese he's buyng, because it wasn't measured in the units he's used to otherwise...and that'd suck.

Mass is how much space something takes up, and weight is how much gravity affects you. Like how much pulling power gravity has on you.

unit of wt. is newton not kg!!!!!