Complete Guide For Class 9 Science Chapter 9 – Gravitation

Welcome to iPrep, your Learning Super App. Our learning resources for Chapter 9, “Gravitation,” in Class 9 are designed to ensure students grasp this fundamental concept with clarity and precision. We provide a range of tools to facilitate a deep understanding of the principles of gravitation, including interactive diagrams, engaging explanations, and practical examples. Students will explore the laws of gravitation, the concept of gravitational force, and its implications in everyday life. Our resources aim to make complex concepts accessible and relatable, helping students build a strong foundation in gravitation essential for further studies in physics and beyond.

The concept of “Gravitation” in Class 9 delves into the foundational principles of how gravitational forces influence the behavior of objects and celestial bodies. It introduces students to the fundamental idea that every object in the universe attracts every other object with a force known as gravity. The chapter explores how this force explains the falling of objects, the orbits of planets and moons, and the variations in weight depending on location. By studying Newton’s laws of motion and the universal law of gravitation, students gain a comprehensive understanding of how gravity impacts both terrestrial and celestial phenomena, setting the stage for more advanced concepts in physics.

What is Gravitation?

Gravity is the force that attracts every object towards every other object. This universal force is responsible for:

• Objects falling towards Earth.
• Planets orbiting the Sun.
• The Moon orbiting the Earth.
• Variations in weight depending on location.

Key Concepts of Gravitation

• Gravitational Attraction: Every object exerts an attractive force on every other object. For example, an apple falls to the ground due to Earth’s gravitational pull. This same force also attracts the Moon towards Earth.
• Sir Isaac Newton: The great scientist who formulated the laws of motion and universal gravitation. According to Newton:
  • An object will remain at rest or in uniform motion unless acted upon by an external force.
  • The force acting on an object is proportional to the rate of change of momentum.
  • For every action, there is an equal and opposite reaction.

Newton’s Laws of Motion

1. First Law: An object remains in a state of rest or uniform motion unless acted upon by an external force.
2. Second Law: The rate of change of momentum is proportional to the applied force.
3. Third Law: Every action has an equal and opposite reaction.

Gravitational Force

The gravitational force between two objects is given by:

Where F is the gravitational force, G is the universal gravity constant, m1 and m2 are the masses of the objects, and d is the distance between their centers. This force is proportional to the product of the masses and inversely proportional to the square of the distance between them.

• Universal Gravity Constant: Denoted by G

Effects of Gravitation

• Orbital Motion: Planets orbit the Sun due to gravitational attraction, and the Moon orbits the Earth.
• Weight Variations: The weight of an object varies depending on its location due to changes in gravitational pull.
• Tides: The gravitational interaction between the Earth, Moon, and Sun causes ocean tides.

Free Fall and Acceleration Due to Gravity

• Free Fall: When an object falls solely under the influence of gravity, it is said to be in free fall. During this process, the object’s velocity increases, while its direction remains unchanged.
• Acceleration Due to Gravity (g): The acceleration experienced by an object –

• Equations of Motion for Free Fall:

• Where u is the initial velocity, v is the final velocity, h is the height, t is the time, and g is the acceleration due to gravity.

Mass and Weight

• Mass: The amount of matter in an object, measured in kilograms, which remains constant regardless of location.
• Weight: The force exerted by gravity on an object, calculated as –

W=m×g

W =Weight of Object

m=Mass of Object

g = the acceleration due to gravity

The weight of the object always remains fixed

Weight varies according to position  

Thrust and Upthrust

• Thrust: The force applied perpendicular to a surface, affecting pressure and area.

• Upthrust: The upward force exerted by a fluid on an object. This force is crucial for objects floating or rising in fluids, such as hot air balloons.

Pressure and Buoyancy

• Pressure: The force exerted per unit area. Solids, liquids, and gases exert pressure on surfaces and container walls.

• Buoyancy: The upward force exerted by a fluid, which helps objects float. This force depends on the volume of displaced fluid, the density of the fluid, and the acceleration due to gravity.

Archimedes’ Principle

Archimedes’ Principle states that a body immersed in a fluid experiences an upward force equal to the weight of the fluid it displaces. This principle is used in designing ships, lactometers, and hydrometers.

Relative Density and Instruments

• Relative Density: The density of a substance compared to the density of water. It helps determine purity and density.

• Hydrometer: Measures fluid density by floating in the liquid.

• Lactometer: Determines the amount of water in milk.

• Submarine: Demonstrates buoyancy by adjusting ballast tanks to float or sink.

This comprehensive guide on “Gravitation” provides a foundational understanding of how the force of gravity governs the interactions between objects and celestial bodies. From the simple act of an apple falling to the ground to the complex orbits of planets and moons, this guide explores the fundamental principles behind gravitational forces. It delves into Newton’s laws of motion, the universal law of gravity, and the role of the gravitational constant, offering insights into how these forces shape our universe. By examining concepts like weight variation, free fall, and buoyancy, readers gain a deeper appreciation for the pivotal role gravity plays in both everyday phenomena and astronomical events.

In conclusion, Class 9 Science Chapter 9 – Gravitation provides a crucial foundation for understanding the forces that govern both our planet and the universe. Through this chapter, students are introduced to the laws of gravity and their applications in daily life, from explaining the orbits of planets to the concept of weight and buoyancy. By mastering these concepts, learners will be well-prepared for more advanced studies in physics and other scientific disciplines.

With iPrep’s engaging resources, including interactive diagrams and detailed explanations, students can fully grasp the importance of gravity. Whether it’s the falling of objects or the movement of celestial bodies, the principles learned in Class 9 Science Chapter 9 – Gravitation offer a comprehensive guide to one of the most fundamental forces in nature. Explore more with iPrep as you dive deeper into the fascinating world of gravitation, ensuring a strong academic foundation for future learning.