CBSE Class 11 Physics Notes Chapter 8 Gravitation
Here, we have provided Chapter 8 Gravitation Notes. Students can view these CBSE Class 11 Physics Notes Chapter 8 Gravitation before exams for better understanding of the chapter.
Ananya Gupta21 Apr, 2024
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CBSE Class 11 Physics Notes Chapter 8: In Chapter 8 of CBSE Class 11 Physics, called "Gravitation," you'll learn about gravity, the force that pulls things towards each other. This chapter talks about how gravity works, especially in space with planets, stars, and galaxies.
You'll understand how gravity affects the movement of planets around the Sun and other celestial bodies. Also, you'll explore concepts like gravitational energy and how it relates to gravity. Plus, you'll learn about Kepler's laws, which explain how planets move around the Sun. Overall, this chapter helps you understand how gravity shapes the universe we live in.CBSE Class 11 Physics Notes Chapter 8 Gravitation PDF
The purpose of CBSE class 11 physics notes Chapter 8 Gravitation in a straight line is to present comprehensive, easy-to-understand material on the subject, step by step. It provide concise, easily legible notes to aid students in rapidly recalling the main ideas prior to the test.CBSE Class 11 Physics Notes Chapter 8 Gravitation PDF
CBSE Class 11 Physics Notes Chapter 8 Gravitation
What is Gravitation?
Gravity is a fundamental force present in the universe, where every object attracts every other object. It's part of the four types of interactions found in nature, including gravitational force, electromagnetic force, strong nuclear force, and weak nuclear forces. Despite being of negligible significance in interactions at the particle level, gravity plays a crucial role in interactions among objects, essentially holding the universe together.Newton’s Law of Gravitation
Newton's Law of Gravitation states that every particle in the universe attracts every other particle 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.
Important Points about Gravitation Force
(i) Gravitational force is a central as well as conservative force. It acts along the line joining the centers of the two masses and conserves mechanical energy. (ii) Despite being fundamental, gravitational force is the weakest force in nature. It is significantly weaker than electrostatic force and nuclear force. (iii) Gravitational force is remarkably weaker than other fundamental forces. It's about 1036 times weaker than the electrostatic force and 1018 times weaker than the nuclear force. (iv) Newton's law of gravitation is applicable to all bodies regardless of their size, shape, or position. It governs the gravitational interaction between any two objects with mass. (v) The gravitational force between the Sun and a planet provides the centripetal force necessary for the planet's orbital motion around the Sun. (vi) The gravitational pull exerted by the Earth on objects near its surface is commonly referred to as gravity. (vii) Newton's third law of motion applies to the force of gravitation, stating that for every action, there's an equal and opposite reaction. Thus, the gravitational forces between two bodies form action-reaction pairs. These points highlight some important aspects of gravitational force: (i) Unlike electrostatic force, gravitational force is independent of the medium between the particles. (ii) Gravitational force is conservative, meaning it conserves mechanical energy. (iii) While Newton's law of gravitation describes the force between point masses, for external points of spherical bodies, the entire mass can be assumed to be concentrated at its center of mass.Acceleration Due to Gravity
The uniform acceleration experienced by a freely falling object due to the gravitational force of the Earth is termed as acceleration due to gravity. Its unit is meters per second squared ( m/s2 ). Being a vector quantity, its direction points towards the center of the Earth. Importantly, the value remains constant regardless of the mass of the object in free fall. Though it may vary slightly from one location to another due to factors like altitude and local geology, for practical purposes, it's commonly considered as 9.8 m/s2 . Comparatively, the acceleration due to gravity on celestial bodies differs significantly. For instance, on the Moon, it's approximately one-sixth of that on Earth, while on the Sun, it's about 27 times greater than that on Earth. These variations values have significant implications for understanding celestial mechanics and space exploration.Factors Affecting Acceleration Due to Gravity
Several factors influence the acceleration due to gravity:Altitude : As altitude increases, the distance from the Earth's center also increases. Consequently, the gravitational force weakens slightly, causing a decrease in the acceleration due to gravity.
Latitude : The Earth is not a perfect sphere; it bulges slightly at the equator due to its rotation. Hence, gravity is slightly weaker at the equator compared to the poles. This variation is due to differences in centrifugal force caused by Earth's rotation.
Depth : Gravity weakens as you move deeper underground. This is because the mass above you exerts less gravitational force.
Mass of the Earth : While not changing significantly over short periods, any change in the mass of the Earth would directly affect the acceleration due to gravity.
Local Geology : Variations in the density and distribution of materials within the Earth's crust can cause local variations in gravitational acceleration.
Centrifugal Force : The Earth's rotation causes a centrifugal force that slightly reduces the effective gravitational force at the equator compared to the poles.
Shape of the Earth : If the Earth were a perfect sphere, the acceleration due to gravity would be uniform everywhere. However, its slightly oblate shape causes small deviations.
Gravitational Field
The gravitational field is a concept in physics that describes the influence of gravity on the space surrounding a massive object. It represents the force exerted on a mass placed at any point in space due to the presence of another mass. In simpler terms, the gravitational field around an object is like an invisible force field that pulls other objects towards it. The strength of the gravitational field at any point depends on the mass of the object creating the field and the distance from that object.Important Points
(i) When a missile is launched with a velocity lower than the escape velocity, the sum of its kinetic energy and potential energy is negative. This indicates that the total mechanical energy of the missile is less than zero, meaning it does not have enough energy to escape the gravitational pull of the Earth. (ii) Jupiter's orbital speed is lower than that of Earth. This is because Jupiter is much larger and has a stronger gravitational pull, requiring less speed for its moons to maintain stable orbits compared to the speed required by objects orbiting Earth. (iii) If a bomb explodes on the Moon, the sound waves produced by the explosion cannot be heard on Earth. This is because sound requires a medium, such as air, to travel through, and the vacuum of space between the Moon and Earth prevents sound from propagating. (iv) If a bottle filled with water at 30°C and sealed with a cork is taken to the Moon and the cork is opened at the Moon's surface, the water will boil. This is because the boiling point of water decreases with decreasing atmospheric pressure, and the Moon has virtually no atmosphere to exert pressure on the water. (v) Inertial mass and gravitational mass are equal to each other in magnitude: (a) Inertial mass is determined by the ratio of force to acceleration. (b) Gravitational mass is calculated by dividing the weight of an object by the acceleration due to gravity. (c) They remain equal to each other in magnitude. (d) Gravitational mass is influenced by the presence of other nearby bodies, while inertial mass remains unaffected by external factors.Kepler’s laws of Planetary Motion
First Law (Law of Ellipses):
- Description: Planets orbit the Sun in elliptical paths, with the Sun at one focus of the ellipse.
- Illustration: Imagine a planet moving around the Sun in an oval-shaped orbit, where the Sun isn't exactly in the center but at one of the focal points.
Second Law (Law of Equal Areas):
- Description: A line joining a planet and the Sun sweeps out equal areas in equal intervals of time.
- Illustration: As the planet moves around its elliptical orbit, it sweeps out areas that are equal in size over equal periods of time. This means the planet moves faster when it's closer to the Sun and slower when it's farther away.
Third Law (Law of Harmonies):
- Description: The square of a planet's orbital period (time it takes to orbit the Sun) is proportional to the cube of the semi-major axis of its orbit (average distance from the Sun).
- Illustration: For all planets, the ratio of the square of their orbital periods to the cube of their average distances from the Sun (P^2/M^3) is the same. This relationship applies universally across all planetary orbits.
Benefits of CBSE Class 11 Physics Notes Chapter 8 Gravitation
Here are some benefits of using CBSE Class 11 Physics Notes Chapter 8 on Gravitation:Comprehensive Coverage : The notes provide a detailed overview of the topic of gravitation, covering key concepts, laws, and principles related to gravitational force.
Clear Explanations : Complex concepts are explained in a clear and concise manner, making it easier for students to understand the principles of gravitation.
Example Problems : The notes often include example problems and solutions, allowing students to practice applying the concepts learned and reinforcing their understanding.
Structured Format : The notes follow a structured format, making it easy for students to organize their study materials and review specific topics as needed.
CBSE Class 11 Physics Notes Chapter 8 FAQs
What is Gravitation?
Gravitation is the force of attraction that exists between any two masses in the universe. It's responsible for phenomena like the Earth's gravitational pull on objects and the motion of planets around the Sun.
What is Newton's Law of Gravitation?
Newton's Law of Gravitation states that every particle in the universe attracts every other particle 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.
How does Gravitational Force Change with Distance?
Gravitational force decreases as the distance between two objects increases. According to Newton's Law of Gravitation, it follows an inverse square law, meaning it decreases with the square of the distance between the objects.
What is Escape Velocity?
Escape velocity is the minimum velocity required for an object to escape the gravitational pull of a massive body without any additional propulsion. It depends on the mass of the body and the distance from its center.
How does Gravitation Impact Planetary Motion?
Gravitation governs the motion of planets around the Sun and satellites around planets. It provides the centripetal force required to keep these objects in their orbits.
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