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I. Chapter Summary:

The chapter Gravitation explains the universal force of gravity discovered by Isaac Newton, which acts between any two bodies in the universe. It covers the Universal Law of Gravitation, free fall, acceleration due to gravity, mass and weight, and Thrust and Pressure. It also explores the buoyant force, Archimedes’ Principle, and relative density, helping students understand why objects float or sink in fluids. This chapter connects the laws of physics to real-world experiences such as falling objects, floating ships, and atmospheric pressure.

II. Key Concepts Covered:

Concept	Description
Gravity	A force of attraction between two masses.
Universal Law of Gravitation	F=Gm1m2r2F = G frac{m_1 m_2}{r^2}F=Gr2m1​m2​​; explains force between any two masses.
Free Fall	When an object falls only under the influence of gravity.
Acceleration due to Gravity (g)	g=9.8 m/s2g = 9.8 , text{m/s}^2g=9.8m/s2 on Earth; varies slightly with location.
Mass vs. Weight	Mass is constant, weight is W=mgW = mgW=mg; depends on gravity.
Thrust and Pressure	Thrust = force applied normally; Pressure = ThrustAreafrac{text{Thrust}}{text{Area}}AreaThrust​.
Buoyancy	Upward force experienced by a body immersed in fluid.
Archimedes’ Principle	Buoyant force = weight of liquid displaced.
Relative Density	RD=Density of substanceDensity of watertext{RD} = frac{text{Density of substance}}{text{Density of water}}RD=Density of waterDensity of substance​.

III. Important Questions:

(A) Multiple Choice Questions (1 Mark):

1. The SI unit of pressure is:
   a) Pascal ✅
   b) Newton
   c) Bar
   d) kg/m³
2. The value of acceleration due to gravity on Earth is:
   a) 10 m/s²
   b) 8.9 m/s²
   c) 9.8 m/s² ✅
   d) 9 m/s
3. The force of gravity acting on a body is called:
   a) Mass
   b) Weight ✅
   c) Density
   d) Thrust
4. When an object is fully immersed in water, the buoyant force is equal to:
   a) Weight of object
   b) Volume of water
   c) Weight of water displaced ✅
   d) Density of object

(B) Short Answer Questions (2/3 Marks):

1. Define buoyancy. Why does a body float or sink in a liquid?
2. Differentiate between mass and weight.
3. Why does a sharp knife cut better than a blunt one?
4. State Archimedes’ Principle and one of its applications.
   – PYQ 2020

(C) Long Answer Questions (5 Marks):

1. Derive the formula for the Universal Law of Gravitation.
2. A stone is thrown vertically upward with a velocity of 10 m/s. Calculate:
   a) Maximum height reached
   b) Total time taken to return to ground
   – PYQ 2021
3. Explain why objects appear lighter in water. Derive relation using Archimedes’ Principle.
4. A body weighs 10 N in air and 8 N when fully immersed in water. Find the buoyant force and the weight of water displaced.
   – PYQ 2022

(D) HOTS (Higher Order Thinking Skills):

1. Why does a rubber ball thrown into water come back to the surface? Explain using density and buoyancy.
2. If the radius of Earth were doubled keeping mass constant, what would be the effect on acceleration due to gravity?

IV. Key Formulas/Concepts:

Formula	Explanation
F=Gm1m2r2F = G frac{m_1 m_2}{r^2}F=Gr2m1​m2​​	Universal law of gravitation
g=GMR2g = frac{GM}{R^2}g=R2GM​	Acceleration due to gravity
W=mgW = mgW=mg	Weight of a body
P=FAP = frac{F}{A}P=AF​	Pressure on a surface
Buoyant force=Weight of fluid displacedtext{Buoyant force} = text{Weight of fluid displaced}Buoyant force=Weight of fluid displaced	Archimedes’ Principle
Relative Density=Density of objectDensity of watertext{Relative Density} = frac{text{Density of object}}{text{Density of water}}Relative Density=Density of waterDensity of object​	Determines floatation

V. Deleted Portions (CBSE 2025–2026):

 No portions have been deleted from this chapter as per the rationalized NCERT textbooks.

VI. Chapter-Wise Marks Bifurcation (Estimated – CBSE 2025–2026):

Chapter	Estimated Marks	Question Types
Gravitation	8–10 Marks	Numerical questions, derivations, concept-based reasoning, HOTS

VII. Previous Year Questions (PYQs):

Year	Marks	Question
2019	3	State Archimedes’ principle and give one use.
2020	5	Derive universal law of gravitation with explanation.
2021	3	What is buoyancy? Why do some objects float and others sink?
2022	5	A ball is thrown vertically upwards with velocity 20 m/s. Calculate maximum height and time of flight.

VIII. Real-World Application Examples to Connect with Topics:

Concept	Application
Buoyancy	Designing ships and submarines
Gravitational Force	Satellite motion, tides, planetary orbits
Pressure	Syringes, knives, hydraulic brakes
Archimedes’ Principle	Life jackets, hydrometers, gold purity testing
Relative Density	Identifying purity of substances, floatation studies

IX. Student Tips & Strategies for Success:

 Time Management:

• Allocate separate time for concepts (like buoyancy, free fall) and numerical practice.
• Use flowcharts to relate concepts.

 Exam Preparation:

• Memorize formulas with units.
• Practice numericals from previous years.
• Revise definitions and conceptual differences regularly.

 Stress Management:

• Use water-tank experiments at home to observe real-life buoyancy.
• Draw labeled diagrams to aid memory (e.g., pressure application, floatation).

X. Career Guidance & Exploration (Class-Specific):

For Classes 9–10:

Stream	Career Paths
Physics	Astrophysicist, Satellite Scientist, Geophysicist
Engineering	Civil, Mechanical, Naval, Aerospace
Applied Science	Meteorologist, Diver, Ship Designer

Foundation Platforms:

• NTSE, NSO, CBSE Science Challenge
• Participation in school science exhibitions with projects on fluid mechanics or gravity models

XI. Important Notes:

•  Use standard units: Newton (N) for force, Pascal (Pa) for pressure, m/s² for acceleration.
•  Use correct direction conventions in free fall and vertical motion.
•  Learn difference tables (mass vs. weight, density vs. relative density, thrust vs. pressure).
•  Graphs and problem-based learning will improve application skills.