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등록자	운영자	날짜	2015-06-15
E-mail	info@pes21.com	홈페이지	http://www.pes21.com
		조회수 : 7971
제 목 : 차원과 단위(Dimension and Unit)
차원과 단위는 간혹 혼돈을 불려 오는 밀접한 관계로 물질적인 기준을 질량(M : Mass), 길이(L: Length), 시간 (T: Time), 온도(K: Kelvin)를 기본차원(Basic Dimension)이라고 정의한다. 또한, 이러한 기본 차원에서 유도된 차원을 유도차원이라고 한다.(속도, 가속도 등등) 여기에 사용되는 단위(Unit)는 이러한 물리적인 차원의 크기를 나타내기 위해 사용하는 것을 단위라고 하며, 종류에는 절대단위와 힘의 단위(F,L,T)를 사용하는데, 절대단위에는 M,K,S 단위와 C,G,S를 사용하며, 힘의 단위에는 SI 단위(N)와 공학단위(Kgf)를 사용한다. 하지만, 간혹, 우리는 단위 사용에 있어 절대 단위와 중력 단위의 상호간에 혼돈을 가지고 있으며, 중량=질량중력가속도 공식에서 질량은 중량/중력가속도로 단위를 환산할 경우 중량(힘)의 단위와 질량 관계에서 착각하는 경우가 더러 있어 아래와 같이 개념을 정리하고자 한다. Sometimes, We are confused to find the matter which used unit is correct after or before transforming the physical analysis in Mechanical calculation. For example, Especially, between an absolute unit and Force unit, either consists of combined unit or transformed unit from which to final mechanical calculation. Generally, we do know that force(F) is equal to Mass by Acceleration, ie F=ma as per Newton"s 2nd law, we can put "g" (Gravity acceleration) as of acceleration velocity here, in this case, can we say that 70Kg is equal to 70Kgf, Obviously 70Kg is Mass unit, on the contrary, 70Kgf is of Force unit using formula of W(Weight)=m(Mass)g(Gravity acceleration), the answer this question is correct, however, we can think about that m(Mass) can be calculated by W(Weight) divided by "g"(Gravity acceleration), 9.8 m/s^2 simply, This would be really to make us confused without corrective comprehension of relative concept between Unit and Force. Corrective answer is 70Kgf of weight that is equal to 70Kg of Mass because the different thing is only unit but 70kgf is of force(70Kg of mass to Gravity acceleration) and then divided by Gravity acceleration(9.8 m/^2), the result of this calculation will be of 70kg (70Kg 9.8 m/s^2 / 9.8 m/s^2). For more explanation, in the density of Air, we can put either about 1.2 kgf/m^3 or 1.2kg/m^3, In this way, for water, either 1,000kg/m^3 or 1,000kgf/m^3, the first one is of mass unit, second one is of force unit, the correct figure is will not be changed as same 1,000 regardless of used unit and, we can use either 1,000kg or 1,000kgf because all of the mass over affected by same Gravity acceleration (9.8m/s^2) or we can put simply Gravity acceleration. In this regard, we can use either mass unit or force unit as same as mechanical calculation, ie we can express that my weight is of 70kgf or 70kg regardless of corrective unit usage. FInally, we can do say 70kgf=70kg as refering to numerical formula, F=mg=70kgf, m=F/g=70kgf/9.8m/s^2, here, f=9.8m/s^2 70kg9.8m/s^2 / 9.8m/s^2 = 70kg so hereby, when we induce force unit by Newton (N), for 70kgf will be equal to 70kg9.8m/s^2 = 686N (N=1kg1m/s^2) and how about 70kg of mass, thereby F=mg, 70kg 9.8m/s^2 = 686N "The End" 2015.06.15. Ryu ChangMyong / P.E

No.		제 목	등록자	날짜	조회
21		차원과 단위(Dimension and Un...	운영자	2015-06-15	7971