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📘 Form One Physics Notes – Density and Relative Density: Concept of Density, Formula, Units, Floating & Sinking, Relative Density Calculations | NECTA-Aligned Study Guide PDF
Master density the simple, exam-ready way — from the density formula and water displacement to relative density and why ships float.

Written specifically for Tanzanian Form One students, this Physics study guide covers the Density and Relative Density topic in clear, structured notes. From the concept of density and its formula to units, worked examples, floating and sinking, and relative density calculations — every concept is explained with practical examples drawn from Tanzanian daily life, including why a wooden log floats on a river, why cooking oil sits on top of water, and why a huge steel ship floats.

✨ What’s Inside
✅ Concept of Density:

Clear definition — mass per unit volume

Formula for Density: ρ = m/V

Memory Triangle — find Density, Mass, or Volume easily

SI Unit: kg/m³ | Common Unit: g/cm³

Conversion Factor: 1 g/cm³ = 1000 kg/m³ (with examples)

Density as a Characteristic Property — unique to each pure substance, used to identify materials and test purity (real gold vs. fake gold)

✅ Worked Examples (3 fully solved):

Example 1: Density of a Regular Solid (wooden block, 5 cm × 4 cm × 2 cm, 32 g) → 0.8 g/cm³

Example 2: Density of an Irregular Solid (stone, 150 g, water displacement 50 cm³ → 110 cm³) → 2.5 g/cm³

Example 3: Density of a Liquid (cooking oil, cylinder 80 g → 172 g, 100 cm³) → 0.92 g/cm³

Diagrams: Rectangular block, before and after submerging

✅ Floating and Sinking in Terms of Density:

Rules of Floating and Sinking — full comparison:

Sinking: ρ_object > ρ_fluid (iron nail in water)

Floating: ρ_object < ρ_fluid (wood on water) Suspended: ρ_object = ρ_fluid Diagram: Density comparison flow chart ✅ Relative Density of a Substance: Clear definition — ratio of density of substance to density of pure water at 4°C Also called Specific Gravity Two Formulas for Relative Density: Using Densities: R.D. = Density of substance / Density of water Using Masses: R.D. = Mass of substance / Mass of equal volume of water Important Characteristics: No Units (ratio of identical quantities) R.D. of Pure Water = 1 Worked Examples (2 fully solved): Example 1: R.D. of copper from density values (8900 kg/m³ ÷ 1000 kg/m³) → 8.9 Example 2: R.D. of liquid Y using masses of equal volumes (40 g ÷ 50 g) → 0.8 Relationship Between Relative Density and Floating/Sinking — full table: R.D. < 1: Floats (ice, cooking oil, wood) R.D. > 1: Sinks (iron, aluminium, stone)

R.D. = 1: Suspends

✅ Revision Exercise 4 — full practice set:

Part A: Multiple-Choice Questions (5)

Part B: Short-Answer Questions (5)

Part C: Calculation Questions (4 — regular solid, irregular solid, liquid, relative density)

Part D: Application & Discussion Questions (2 — Floating Ship Paradox, Ice Floating on Water)

✅ Diagrams — Memory triangle, density comparison chart, water displacement

🎯 Perfect For
Form One students studying Physics

NECTA exam preparation and revision

Teachers looking for ready-made teaching material

Parents helping their children study at home

Anyone who wants to understand density, floating, sinking, and relative density

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🔑 Keywords
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