Lecture Notes: Specific Gravity

Definition of Specific Gravity

• Specific Gravity: Ratio of the density of an object to the density of water.
  • Formula: [ \text{Specific gravity} = \frac{\text{Density of object}}{\text{Density of water}} ]
• Density of Water: 1,000 kilograms per meter cubed (kg/m³).
• Example:
  • Gold: Density = 19,300 kg/m³, Specific Gravity = 19.3
  • Ketchup: Density = 1,400 kg/m³, Specific Gravity = 1.4
• Units: No units for specific gravity as they cancel out in the ratio.

Importance of Specific Gravity

• Floating Objects:
  • Specific gravity indicates the fraction of an object submerged when floating.
  • Example:
    • Wood with specific gravity of 0.2: 20% submerged.
    • Wood with specific gravity of 0.6: 60% submerged.
• Icebergs:
  • Ice density = 920 kg/m³, Specific Gravity = 0.92
  • 92% of an iceberg's volume is underwater.

Sinking Objects

• Objects with a specific gravity > 1 sink in water.
• 100% of the object's volume will be submerged if it sinks.
• Example:
  • A cube with density 2,700 kg/m³, Specific Gravity = 2.7, will sink.

Specific Gravity with Other Liquids

• Specific gravity can be with respect to liquids other than water.
• Example with Oil:
  • Wood density = 638 kg/m³
  • Oil density = 850 kg/m³
  • Specific gravity with oil = 0.75
  • 75% of the wood's volume is submerged when floating in oil.