Lecture on Specific Gravity

Definition

• Specific Gravity: A measure that compares the density of an object to the density of water.
  • Formula: Specific Gravity = Density of an object / Density of water
  • Density of water: 1,000 kilograms per meter cubed.
  • No units: Because it is a ratio of two densities, the units cancel out.

Examples of Specific Gravity

• Gold:
  • Density: 19,300 kilograms per meter cubed.
  • Specific Gravity: 19.3
• Ketchup:
  • Density: 1,400 kilograms per meter cubed.
  • Specific Gravity: 1.4

Importance of Specific Gravity

• Floating Objects:
  • Specific gravity indicates the fraction of an object that will be submerged when floating.
  • Example:
    • Wood with specific gravity 0.2: 20% submerged.
    • Wood with specific gravity 0.6: 60% submerged.
  • Ice:
    • Density: 920 kilograms per meter cubed.
    • Specific Gravity: 0.92
    • 92% of an iceberg is submerged.

Sinking Objects

• Objects with specific gravity > 1:
  • Will sink in water.
  • Maximum submersion: 100% of the object's volume.

Specific Gravity with Other Liquids

• Sometimes calculated with liquids other than water.
• Example:
  • Wood density: 638 kilograms per meter cubed.
  • Oil density: 850 kilograms per meter cubed.
  • Specific gravity calculation shows 75% of the wood's volume submerged in oil.

Summary

• Specific gravity is a useful measure for determining how much of an object will be submerged in a liquid, based on the object's density compared to the liquid's density.
• While typically related to water, it can be adapted for use with other liquids.