The CBSE Class 9 Science chapter "Gravitation" pulls students into the fundamental force that governs the motion of objects in the universe. This engaging chapter explains how gravity not only keeps us grounded but also orchestrates the celestial dance of planets, stars, and galaxies.
Introduction to CBSE Class 9 Science Chapter "Gravitation"
In “Gravitation,” Class 9 students are introduced to the invisible force that holds the universe together. The chapter starts by defining gravitation as the force of attraction between any two bodies in the universe. It discusses the universal law of gravitation proposed by Sir Isaac Newton, which quantifies this force and explains 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.
The chapter then takes a closer look at the gravitational force on Earth, which gives us the phenomenon of weight. It differentiates between mass and weight, emphasizing that mass is invariant while weight is the force of gravity acting on that mass. Students explore the concept of free fall and the acceleration due to gravity, understanding that all objects fall towards the Earth at the same rate when air resistance is negligible.
It also covers important concepts like the significance of ‘g’, the acceleration due to gravity, and how it varies from one celestial body to another, as well as from place to place on the Earth. The chapter ends with an examination of buoyancy, the thrust of a liquid, and Archimedes’ principle, which explains why objects float or sink when placed in a fluid.
Assignments for CBSE Class 9 Science Chapter “Gravitation”
- Calculate ‘g’: Using the formula �=��1�2�2, calculate the force of gravity between two objects.
- Mass vs. Weight: List household objects, their estimated masses, and calculate their weight on Earth (assuming �=9.8�/�2).
- Free Fall Experiment: Drop two different objects of varying masses from a height and record the time taken to hit the ground.
- Buoyancy Exploration: Place objects of different densities in water to explore buoyancy and determine whether they float or sink.
- Archimedes’ Principle Application: Experiment with objects submerged in liquids to measure displaced water and relate it to the objects’ buoyancy.
Conclusion
“Gravitation” is a pivotal chapter that offers a glimpse into the universal law that affects every aspect of our lives and the cosmos. Understanding this fundamental force equips students with a perspective that transcends their everyday experience, enabling them to appreciate the grandeur of the cosmos and the scientific principles that underpin it.
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Questions and Answers for CBSE Class 9 Science Chapter "Gravitation"
- Q1: What is the universal law of gravitation?
ANS: 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. - Q2: How does gravity affect the motion of celestial bodies?
ANS: Gravity causes celestial bodies to attract each other, which results in the orbiting of planets around stars, moons around planets, and the formation of galaxies. - Q3: What is the difference between mass and weight?
ANS: Mass is the measure of the amount of matter in an object and is constant, whereas weight is the force exerted by gravity on that object and can change depending on the gravitational pull. - Q4: Why do all objects fall at the same rate in a vacuum?
ANS: In a vacuum, there is no air resistance to slow down objects, so the only force acting on them is gravity, which causes them to accelerate at the same rate. - Q5: How does the value of ‘g’ vary on Earth?
ANS: The value of ‘g’ varies slightly due to Earth’s rotation, its elliptical shape, and altitude differences – it’s less at the equator than at the poles and decreases with altitude. - Q6: What is Archimedes’ principle?
ANS: Archimedes’ principle states that when a body is partially or completely submerged in a fluid, it experiences an upward force equal to the weight of the fluid displaced by it. - Q7: What role does density play in the sinking or floating of an object?
ANS: An object will float if it is less dense than the fluid it is placed in and sink if it is denser than the fluid. - Q8: How do astronauts experience weightlessness in space?
ANS: Astronauts experience weightlessness in space because they are in free fall around the Earth, and the gravitational force is the only force acting on them, eliminating the support force that we feel as weight on the surface. - Q9: What is free fall?
ANS: Free fall is the motion of an object where gravity is the only force acting upon it, with air resistance being negligible or absent. - Q10: Why is understanding gravitation important in science?
ANS: Understanding gravitation is important in science for explaining the motions of objects on Earth and in space, understanding tides, planetary orbits, and for various technologies that depend on gravitational calculations.
