物理問題,about the newton and the metric unit of weight!!!!!

I think the point is not whether Newton is an IS unit.
Kg is also an IS unit but it is as popular as pound.
I think the point is that people are used to use mass unit (e.g. kg, pound) in
place of force unit for their body weight (a kind of force).
Newton is an unit of force. To most people, it sounds strange to relate their weight with force.

I don't agree with physics8801

First, Beijng is not at a lower altitude than Hong Kong, so the value of 'g' will not be bigger there.

Second, even if you use kg , you still won't have a constant weight.
If you measure your body weight using a bothroom scale (the marking is in kg), you will still get different measurements in different places on earth.

2008-10-25 13:08:19 補充：
So, the fact that g is not constant, although true, is not the determining factor why people don't use Newton.

The 'lb' or 'kg' that we use for measuring body weight in daily life are actually refer to respectively 'lbf (pound-force)' or 'kgf (kilogram-force)' in physics. These are units of force.

Why the unit 'Newton' is not commonly used in daily life? It is because to convert from the mass unit of 'kg' or the force unit of 'kgf' to N, the value of the acceleration due to gravity g is inevitably involved. But the value of g, in fact, is not a constant, it varies with location of the earth and decreases with altitude. Thus, if a person weights, say 700 N, at sea level in Hong Kong, he may appear to weight more than 700 N in Beijing (because the value of g in Beijing is slightly larger than that in HK). He would weight less in the highland of Tibet because of the lower value of g at high altitude. Therefore, you would not have a 'constant weight' to quote with if you choose to express your weight in the unit of N.

WEIGHT既SI UNIT係NEWTONS (N)
你係唔同既星球會有唔同既WEIGHT係因為佢地既GRAVITY唔同
F=mg

mass既si unit 係kilograms (kg)
你係邊度你既mass都係一樣

係physics既角度 人地問你既weight 你答幾多kg係好好笑 因為唔岩unit

It is because all SI units are defined to be easily put in the natural or physical equations, just like E=KE+PE, KE=1/2 mv^2, PE=mgh, if you use SI units, we don't need to add new constants.

As a result the new units will be different from those units used in old times, as people were using them for such a long period of time, it's hard to ask them to use SI units. Like pounds, feet and etc.

The metric unit of weight is one of the SI units.