Physics 2A Practical — Mass vs Volume (Wooden Blocks)

Objectives: Physics 2A Practical — Mass vs Volume (Wooden Blocks)

Physics 2A Practical 2025

PHYSICS 2A PRACTICAL 2025

Experiment: Mass and Volume of Wooden Blocks

Apparatus Provided:

  • Five wooden blocks (B1, B2, B3, B4, B5)
  • Beam balance
  • Meter rule
  • Beaker with liquid L
  • Vernier caliper

Procedure:

  1. Using a beam balance measure the mass of block B1.
  2. Using Vernier caliper measure the dimensions (L × W × t) of the block B1 and calculate its volume.
  3. Repeat steps for blocks B2, B3, B4, B5.
  4. Tabulate the results as shown below:
Block Mass (g) Length (cm) Width (cm) Thickness (cm) Volume (cm³)
B1...............
B2...............
B3...............
B4...............
B5...............

Questions & Answers:

(i) Plot the graph of Mass (g) against Volume (cm³)
The graph is a straight line passing through the origin because mass is directly proportional to volume for uniform material.

Volume (cm³) Mass (g)
(ii) Find the slope of your graph
Slope = ΔMass / ΔVolume Example: If (M2, V2) = (120 g, 100 cm³) and (M1, V1) = (60 g, 50 cm³), then slope = (120 - 60) / (100 - 50) = 60 / 50 = 1.2 g/cm³.
(iii) State the physical meaning of the slope
The slope represents the density of the wooden material (ρ). That is, ρ = Mass / Volume in g/cm³.
(iv) State what happens if block B5 is immersed in liquid L
If the density of block B5 is less than the density of liquid L, it will float. If the density of block B5 is greater than the density of liquid L, it will sink.
(v) State three sources of error and their precautions
  1. Error: Parallax error when reading Vernier caliper. Precaution: Ensure eye is at the same level with scale.
  2. Error: Zero error in Vernier caliper or beam balance. Precaution: Check and correct zero error before measurements.
  3. Error: Irregular shape or rough edges of blocks. Precaution: Take several measurements and average them.
Physics 2A Practical — Mass vs Volume (Wooden Blocks)

PHYSICS 2A PRACTICAL (2025)

Topic: Relationship between Mass and Volume for wooden blocks (density from a graph)

Apparatus

Five wooden blocks B1–B5, beam balance, meter rule, beaker with liquid L (water unless stated), Vernier caliper.

Measured Data

Dimensions measured with a Vernier caliper. Volumes computed as V = L × W × t.
Block Mass (g) Length L (cm) Width W (cm) Thickness t (cm) Volume V (cm³)
B137.5104280
B282.61253180
B3118.81363234
B4162.51574420
B5430.6201051000

(i) Graph of Mass (g) against Volume (cm³)

0 500 1000 0 200 400 600 Volume, V (cm³) Mass, M (g)

The points lie close to a straight line through the origin ⇒ mass ∝ volume.

(ii) Slope of the Graph

Using slope formula:

Slope m = ΔM / ΔV
Take two far points: (1000, 430.6) and (80, 37.5)

m = (430.6 - 37.5) / (1000 - 80)
  = 393.1 / 920
  ≈ 0.428 g·cm⁻³

(iii) Physical Meaning of the Slope

The slope represents density (ρ) of the wood.
From formula: Mass = Density × Volume → M = ρV. The line equation is M = mV ⇒ m = ρ. So density of the wood is about 0.429 g/cm³.

(iv) Floating Test

If the block is placed in water (ρ = 1.0 g/cm³), wood has density 0.429 g/cm³, which is less. Therefore, the block floats on water but only partly submerged.

(v) Errors and Precautions

  1. Zero error of balance and Vernier caliper. → Precaution: reset zero before each measurement.
  2. Parallax error when reading scales. → Precaution: observe at eye level.
  3. Block not perfectly rectangular. → Precaution: measure at several positions and take average.
  4. Mass may change due to moisture. → Precaution: keep block dry and weigh immediately.

Conclusion

Mass is directly proportional to volume. The slope of the graph equals density ≈ 0.429 g/cm³. Wooden block floats in water.

Detailed Study Notes

1. Formulae to Remember

  • Volume of block: V = Length × Width × Thickness.
  • Density: ρ = Mass / Volume.
  • Slope of M–V graph = Density.

2. Real-Life Examples

  • A log of wood floats in river water because its density is lower than water.
  • Iron nails sink in water because density of iron (≈7.8 g/cm³) is greater than water.
  • Ships are made of steel but float due to hollow design that increases total volume and reduces average density.

3. Common Mistakes to Avoid

  • Forgetting to convert units (e.g., cm³ to m³ when using SI).
  • Drawing graph with mass on x-axis instead of volume. (Correct: Volume on x, Mass on y).
  • Using one reading to calculate slope. (Correct: choose two far-apart points on best-fit line).
  • Assuming density depends on size of block. (It is a property of material, not size).

4. Graph Interpretation Tips

  • A straight line through origin shows direct proportionality.
  • The steeper the line, the higher the density.
  • If line does not pass through origin, there is systematic error.

Reference Book: N/A

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