Buoyant Force പ്ലവക്ഷമബലം
The chapter opens with INS Vikrant, the giant aircraft carrier built at Cochin Shipyard, sailing past the Chinese fishing nets of Kochi. A boy wonders: “Even a very light iron nail sinks in water. So how does a ship that weighs thousands of tonnes float on the sea?” By the end of this chapter you will answer him. You will discover the upward push that every liquid and gas gives to things in it (the buoyant force) and learn to measure it with a spring balance. You will find out what makes it bigger, and meet Archimedes' principle and the principle of floatation. You will also see how a lactometer at the milk society catches milk mixed with water. This interactive, animated self-study guide starts from the basics – mass and weight, volume, density and pressure. It explains every idea with Kerala examples, answers every textbook question, and ends with a revision sheet and a model test.
The chapter in one picture
Left: the sea pushes the ship up with the buoyant force (പ്ലവക്ഷമബലം, green arrow). As containers are loaded, the ship's weight (ഭാരം, red arrow) grows, and the ship sinks a little deeper. The deeper it sits, the more water it pushes aside, and the bigger the buoyant force becomes. It settles where the buoyant force is exactly equal to its weight – the two arrows are always the same length. This is the principle of floatation (പ്ലവനതത്വം, page 8). Right: a 5 g iron nail can push aside only a tiny amount of water (less than 1 cm³), so the buoyant force on it is only about one-eighth of its weight. It sinks (മുങ്ങുക). The ship is made of iron too, but its hollow shape pushes aside a huge volume of water. (Numbers: a box-shaped hull 200 m × 30 m in sea water of density ≈ 1025 kg/m³; the vertical scale of the ship is stretched so that you can see the change.)
How to use this guide
🎬 Watch the animations
Ships settle, stones sink, water overflows into beakers and hydrometers bob up and down, one step at a time. Press Next ▶ or ▶▶ Auto play.
🧪 Do the virtual experiments
Lower objects into different liquids on a spring balance, load a boat and test a lactometer in milk. Every reading is worked out with real physics (F = ρ V g, W = m g). The textbook activities have no fixed numbers, so these are sample readings. Your own readings will differ slightly.
✍️ Try before you see
Every numerical is laid out the exam way: Given → Formula → Substitution → Answer. Use 💡 Show a hint first and work in your notebook. Then open ✅ Show final answer.
📖 Textbook words
Purple മലയാളം words are the exact terms used in your textbook (pages 95–106), so you can match this guide with your book and write answers in either language.
Learning path
Follow the pages in order. If you are already confident with mass and weight, the newton and kgwt, volume, density and pressure, you can skim pages 1–4. Still try their quizzes, because the chapter uses these ideas on every page.
Quick glossary (Malayalam ↔ English)
| Textbook term | English | Meaning |
|---|---|---|
| പ്ലവക്ഷമബലം | Buoyant force | The chapter title: the upward force a fluid exerts on an object fully or partly immersed in it |
| ദ്രവങ്ങൾ | Fluids | Liquids and gases together – anything that can flow |
| ദ്രാവകങ്ങൾ / ദ്രാവകം | Liquids / liquid | Water, oil, glycerine, kerosene, milk… |
| വാതകങ്ങൾ | Gases | Air, helium, carbon dioxide… (air also gives a buoyant force) |
| ജലോപരിതലം | Water surface | The top surface of the water |
| ഭാരം | Weight | The force with which the Earth pulls an object: W = m g, in newtons |
| മാസ് | Mass | The amount of matter in an object, in kilograms |
| കിലോഗ്രാം ഭാരം (kgwt) | Kilogram weight | The weight of a 1 kg mass: 1 kgwt = 9.8 N |
| സ്പ്രിങ് ബാലൻസ് | Spring balance | An instrument whose spring stretches to show a force (weight) in newtons |
| തൂക്കക്കട്ടി | Standard weight (mass piece) | A metal piece of known mass, such as 100 g |
| വായുവിലെ ഭാരം (W₁) | Weight in air | Spring-balance reading with the object hanging in air |
| ജലത്തിലെ ഭാരം (W₂) | Weight in water | Spring-balance reading with the object fully immersed in water |
| ഭാരക്കുറവ് / ഭാരനഷ്ടം | Apparent loss of weight | W₁ − W₂: how much lighter the object seems in the liquid; it equals the buoyant force |
| പൂരിത ഉപ്പുലായനി | Saturated salt solution | Water in which no more salt will dissolve; denser than water |
| ഗ്ലിസറിൻ · മണ്ണെണ്ണ · വെളിച്ചെണ്ണ | Glycerine · kerosene · coconut oil | The liquids in Table 5.3 (1260, 810 and 920 kg/m³) |
| സാന്ദ്രത | Density | Mass per unit volume, ρ = m/V, in kg/m³ |
| വ്യാപ്തം | Volume | The space an object occupies, in m³ or cm³ |
| ആദേശം ചെയ്ത ജലം | Displaced water | The water pushed aside by the part of an object that is under water |
| കവിഞ്ഞൊഴുകിയ ജലം | Overflowing water | The water that flows out of a full overflow jar when an object is lowered in |
| ആർക്കിമിഡീസ് തത്വം | Archimedes' principle | The buoyant force on an object in a fluid equals the weight of the fluid it displaces |
| പ്ലവനതത്വം | Principle of floatation | A floating object displaces fluid whose weight equals its own weight |
| പൊങ്ങിക്കിടക്കുക / മുങ്ങുക | Float / sink | Stay at the surface with part above it / go down to the bottom |
| ആപേക്ഷികസാന്ദ്രത | Relative density | Density of a substance ÷ density of water; a number with no unit |
| ഹൈഡ്രോമീറ്റർ | Hydrometer | A floating instrument that measures the relative density of liquids |
| ലാക്ടോമീറ്റർ | Lactometer | A hydrometer for milk; detects added water |
| മായം ചേർക്കൽ | Adulteration | Mixing a cheaper substance into food (such as water into milk) – an offence |
| ചാവുകടൽ | Dead Sea | A very salty lake between Israel and Jordan; so dense that people float easily |
| ലൈഫ് ജാക്കറ്റ് | Life jacket | A light jacket filled with foam or air that keeps a person afloat |
| പ്രവർത്തനം · സയൻസ് ഡയറി | Activity · science diary | Things to do, and the notebook where you write what you observed |
| വിലയിരുത്താം · തുടർപ്രവർത്തനങ്ങൾ | Let us assess · extended activities | The end-of-chapter questions and projects (solved on page 11) |
🌐 Explore online (optional)
Everything in this guide works offline: each page is a single file with no internet needed. Some pages also have blue “🌐 Explore online” boxes. They link to free websites and interactive simulations, including the PhET “Buoyancy” and “Density” simulations, like the Buoyant Force simulation your textbook mentions. Those links need internet and open in a new tab. All of them are collected in the resources hub on page 12.
- 📄 Building Science Concepts: Floating and sinking Science Learning Hub, New Zealand
Big-picture guide to density, displacement and floating, with common mistakes explained. - 📄 Science Snacks: buoyancy Exploratorium
A collection of easy home experiments on buoyancy and floating.
Made for self-learning. Works offline – every page is a single file. Study material prepared by Claude for Madhu's family study folder, October 2026.