Fluid Dynamics
Density and specific gravity, the Cat A fluid-dynamics scope.
Fluid dynamics (Cat A), summary notes
- Density is how much mass is packed into a given volume, it's why a small lead weight is heavier than a large block of foam.
- Specific gravity (SG) compares a substance's density to that of water (1,000 kg/m³). Water has an SG of 1; anything with SG < 1 floats on water, SG > 1 sinks.
- Density and SG are used constantly in maintenance to identify fluids and check fuel and hydraulic fluid specifications.
- Density
- ρ = m / V (kg/m³)
- Specific gravity
- SG = ρ(substance) / ρ(water)
A block has a mass of 2 kg and a volume of 0.001 m³. What is its density?
ρ = m / V = 2 / 0.001 = 2,000 kg/m³.
A fuel has a density of 800 kg/m³. What is its specific gravity?
SG = 800 / 1,000 = 0.8, less than 1, so it floats on water.
Density, specific gravity & buoyancy
Pressure & hydraulics
Fluid-flow concept map
Fluid Flow
Density & SG quiz
Fluids, Density & Specific Gravity (Cat A)
1. Density is defined as:
Mass per unit volumeVolume per massForce per area2. The SI unit of density is:
kg/m³kgm³3. Density equals mass divided by:
VolumeAreaTime4. A 200 kg object of volume 0.1 m³ has a density of:
2000 kg/m³20 kg/m³0.0005 kg/m³5. The density of pure water is about:
1000 kg/m³100 kg/m³1 kg/m³6. Specific gravity compares a substance's density to that of:
WaterAirMercury7. Specific gravity has units of:
None (it is a ratio)kg/m³N8. A substance with SG 2 is how many times as dense as water?
20.5209. An object with SG less than 1 will:
Float on waterSink in waterDissolve10. An object with SG greater than 1 will:
Sink in waterFloatEvaporate11. The specific gravity of water is:
101012. A liquid of density 800 kg/m³ has a specific gravity of:
0.888013. Mass equals density multiplied by:
VolumeAreaTime14. Volume equals mass divided by:
DensityAreaForce15. A 2 m³ tank of fuel (density 750 kg/m³) holds a mass of:
1500 kg375 kg1502 kg