Class 11 Physics - CBSE
Gravitation
The chapter Gravitation in Class 11 Physics explores the universal force of attraction acting between all matter in the universe. Building upon Johannes Kepler's laws of planetary motion, Sir Isaac Newton formulated the Universal Law of Gravitation. Students will study the variation of acceleration due to gravity with altitude, depth, and the earth's rotation. The chapter also covers gravitational potential energy, escape velocity, and the orbital motion of satellites. This is a high-scoring and conceptually vital chapter for CBSE board exams as well as competitive entrance tests like NEET and JEE.
Start Learning FreeKey Concepts
Newton's Law of Gravitation
Every particle attracts every other particle in the universe with a force proportional to the product of their masses and inversely proportional to the square of the distance between them.
Acceleration Due to Gravity (g)
The acceleration produced in a freely falling body due to the earth's gravitational pull, which varies with altitude, depth, shape of the earth, and latitude.
Gravitational Potential Energy
The work done in bringing a mass from infinity to a point in the gravitational field, given by the expression U = -GMm/r.
Escape Velocity
The minimum velocity required for an object to break free from the gravitational pull of a planet or celestial body and escape into space.
Kepler's Laws of Planetary Motion
Three empirical laws describing planetary orbits: the law of orbits (ellipses), the law of areas (equal areas in equal times), and the law of periods (T squared proportional to a cubed).
Important Formulas
Board Exam Info
In the CBSE Class 11 Physics board/school examinations, Gravitation typically carries around 5 to 7 marks. Common question types include numerical problems on the variation of 'g' with height and depth, derivations of escape velocity and orbital velocity, statements and conceptual applications of Kepler's laws, and questions regarding gravitational potential energy.
Frequently Asked Questions
Why is gravitational potential energy always negative?
It is negative because the reference point is chosen at infinity where potential energy is zero, and as the body moves closer to the source of gravity, work is done by the field, making the energy decrease below zero.
Does the escape velocity of an object depend on its mass?
No, the mass of the escaping object cancels out in the escape velocity formula (v_e = sqrt(2GM/R)), meaning a feather and a rocket require the same initial speed to escape Earth's gravity.
What is the difference between g (acceleration due to gravity) and G (universal gravitational constant)?
G is a universal constant with a fixed value everywhere in the universe, whereas g is an acceleration whose value changes depending on the mass, radius, and location on a planet.
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