Lecture Notes: Determining Densities of Solid Objects

Overview

• Goal: Understand how to calculate the densities of regular and irregular solid objects.
• Importance: This is a required practical and can appear in exams.
• Key Concept: Density = mass/volume, measured in kg/m³.

Density Calculation Equation

• Equation: Density = Mass (kg) / Volume (m³)
• Units: kg/m³
• Note: Equation is not provided in exams.

Categories of Objects

• Regular Objects: Easy to measure dimensions (e.g., a cube).
• Irregular Objects: Difficult to measure dimensions directly (e.g., a vase).

Determining Density of Regular Objects

1. Measuring Mass:
   • Use a balance to determine the mass.
   • Example: Mass of a cube = 0.5 kg.
2. Measuring Volume:
   • Use a ruler to measure dimensions.
   • For a cube: Measure length of one side.
   • Example:
     • Side length = 120 mm = 0.12 m
     • Volume = side³ = 0.12 m × 0.12 m × 0.12 m = 0.001728 m³
3. Calculating Density:
   • Put mass and volume into the density equation.
   • Example: Density = 0.5 kg / 0.001728 m³ = 289.35 kg/m³ (to two decimal places)

Determining Density of Irregular Objects

1. Measuring Mass:
   • Use a balance as with regular objects.
2. Measuring Volume (Displacement Method):
   • Use a Eureka can filled with water.
   • As the object is submerged, water is displaced.
   • Measure the displaced water using a measuring cylinder.
   • The volume of displaced water = volume of the object.

Conclusion

• You should now be able to describe the methods to determine densities of both regular and irregular solid objects.
• Additional resources and practice questions are available in the revision workbook linked in the video.