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Important Points: Gravitation | Science Class 9 PDF Download

Introduction

  • Gravitation is a fundamental natural force that attracts all objects with mass towards each other.
  • This chapter delves into the concepts of gravitation, universal law of gravitation, free fall, mass, weight, thrust, pressure, and Archimedes’ principle.

Universal Law of Gravitation

  • Every object in the universe attracts every other object with a force directly proportional to the product of their masses and inversely proportional to the square of the distance between them.
  • This force acts along the line joining the centers of the two objects.

Gravitational Force and Motion

  • Gravitational force influences the motion of planets and natural satellites, as well as objects on Earth.
  • Objects fall towards the Earth due to Earth’s gravitational pull.

Free Fall

  • Free fall occurs when objects fall towards Earth only under the influence of gravity, without any other forces acting on them (like air resistance).
  • All objects experience the same acceleration due to gravity, denoted by 'g', close to the Earth’s surface.

Mass and Weight

  • Mass is a measure of an object's inertia and remains constant regardless of location.
  • Weight is the force exerted by gravity on an object. It varies depending on the location due to changes in gravitational force.

Thrust and Pressure

  • Thrust is the force acting on an object in a particular direction.
  • Pressure is defined as thrust per unit area and varies based on the area over which a force is distributed.

Buoyancy and Archimedes’ Principle

  • Buoyancy is the upward force exerted by fluids (liquids and gases) on immersed objects.
  • Archimedes’ Principle states that when a body is fully or partially submerged in a fluid, it experiences an upward force equal to the weight of the fluid displaced by it.
  • Objects float or sink in fluids based on their density relative to the fluid.

Applications

  • The principles of gravitation and buoyancy are crucial in various fields, including aerospace, marine engineering, and fluid mechanics.
  • These concepts help in understanding phenomena like tides, orbital motion of celestial bodies, and the behavior of objects in different fluids.

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FAQs on Important Points: Gravitation - Science Class 9

1. What is the Universal Law of Gravitation?
The Universal Law of Gravitation states that every object in the universe attracts every other object with a force that is directly proportional to the product of their masses and inversely proportional to the square of the distance between their centers. This force of attraction is known as gravitational force.
2. How does the Universal Law of Gravitation apply to celestial bodies?
The Universal Law of Gravitation applies to celestial bodies such as planets, moons, and stars. It explains why these objects orbit around each other in our solar system and beyond. The gravitational force between these celestial bodies keeps them in their respective orbits and governs their motion.
3. What is buoyancy and how does it relate to Archimedes' Principle?
Buoyancy is the upward force exerted by a fluid (liquid or gas) on an object submerged in it. Archimedes' Principle states that the buoyant force experienced by an object submerged in a fluid is equal to the weight of the fluid displaced by the object. In simpler terms, it means that an object will float in a fluid if its weight is less than the weight of the fluid it displaces.
4. How does the density of an object affect its buoyancy?
The density of an object determines its buoyancy. If the density of an object is less than the density of the fluid it is submerged in, it will float. If the density of an object is greater than the density of the fluid, it will sink. The buoyant force acting on an object is directly proportional to the density of the fluid and the volume of the fluid displaced.
5. How is Archimedes' Principle used in real-life applications?
Archimedes' Principle is used in various real-life applications. Some examples include the design of ships and submarines, hot air balloons, and the determination of purity in precious metals. It is also used in understanding the behavior of objects in water, such as why some objects float while others sink.
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