밀도 단위 실수 (g/cm³ vs kg/m³)
ρ = m/V is simple — until 단위 disagree. These traps cost marks in 밀도 and buoyancy questions.
ρ = m / V — 1 g/cm³ = 1000 kg/m³ · 1 L = 0.001 m³
함정 1: Mixing grams with cubic metres
틀림: m = 250 g, V = 0.00025 m³ → ρ = 250 / 0.00025 without converting 질량.
맞음: 변환하세요 m = 0.250 kg first → ρ = 0.250 / 0.00025 = 1000 kg/m³.
수정: Pair g with cm³ (→ g/cm³) or kg with m³ (→ kg/m³).
함정 2: Treating liters as cubic metres
틀림: V = 2 L into ρ = m/V with m kg 단위로 as if V were 2 m³.
맞음: 2 L = 0.002 m³. Off-by-1000 errors are almost always liters vs m³.
수정: 1 L = 0.001 m³ = 1000 cm³.
함정 3: Forgetting 1 g/cm³ = 1000 kg/m³
틀림: Aluminum 2.7 g/cm³ reported as 2.7 kg/m³ in an SI buoyancy 공식.
맞음: 2.7 g/cm³ = 2700 kg/m³.
수정: Water is about 1 g/cm³ or 1000 kg/m³ — use that as a sanity 확인.
함정 4: Putting 물체 밀도 into Fb = ρVg
틀림: Using steel 밀도 for ρ when finding buoyant 힘 in water.
맞음: ρ in Fb = ρVg is the fluid 밀도. Object 밀도 is for float/sink comparison.
수정: Fresh water ≈ 1000 kg/m³ unless the problem gives salt water or another fluid.
함정 5: Comparing 밀도 to 무게
틀림: “밀도 800 kg/m³ is less than 무게 20 N so it floats.”
맞음: 비교 densities (물체 vs fluid) or 힘s (W vs Fb) — never 밀도 to newtons.
수정: Same kind of quantity on both sides of a comparison.
결론
Match 질량 and volume 단위 나누기 전에, convert g/cm³ ↔ kg/m³ with ×1000, and put fluid 밀도 — not 물체 밀도 — into Fb = ρVg.
FAQ
무엇인가요 the 밀도 공식?
ρ = m / V. 식 변형 to m = ρV or V = m/ρ with matching 단위.
어떻게 하나요 convert g/cm³ to kg/m³?
곱하세요 by 1000. 예제: 2.7 g/cm³ → 2700 kg/m³.
연습 ρ = m/V · 밀도 계산기 · 부력 계산기 · 무게 계산기 · 단위 변환하세요er