Class 11 Physics - PUNJAB
Gravitation
The chapter Gravitation in Class 11 Physics under PSEB explores the fundamental force of attraction between any two objects in the universe. Students learn about Newton's Universal Law of Gravitation, acceleration due to gravity (g) and its variation with height, depth, and shape of the Earth. The chapter also covers Kepler's planetary motion laws, gravitational potential energy, escape velocity, and the mechanics of orbital motion of satellites. This is a high-yield chapter for Punjab Board exams as numerical problems based on escape velocity, orbital velocity, and variation of 'g' frequently appear in both short and long-answer formats.
Start Learning FreeKey Concepts
Newton's Law of Gravitation
Every particle attracts every other particle with a force directly proportional to the product of their masses and inversely proportional to the square of the distance between them.
Acceleration Due to Gravity (g)
The uniform acceleration produced in a freely falling body due to the Earth's gravitational pull, whose value changes with altitude, depth, and latitude.
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).
Gravitational Potential Energy
The work done in bringing a mass from infinity to a point in gravitational field, given by U = -GMm/r, representing bound systems with negative energy.
Escape Velocity
The minimum velocity required for an object to break free from the gravitational pull of a planet permanently, independent of the mass of the escaping body.
Important Formulas
Board Exam Info
In the Punjab School Education Board (PSEB) Class 11 Physics exam, Gravitation typically carries around 4 to 6 marks. Questions usually include derivations for the variation of 'g' with height and depth, definition of escape velocity and orbital velocity, and numerical problems based on Kepler's laws or gravitational potential energy.
Frequently Asked Questions
Why is gravitational potential energy always negative?
It is negative because the reference point (zero potential energy) is chosen at infinity, and as an object moves closer to the source mass, attractive forces do positive work, reducing the total potential energy below zero.
Does escape velocity depend on the mass of the body?
No, escape velocity is independent of the mass of the escaping object because mass appears on both sides of the energy conservation equation and cancels out (v_e = sqrt(2GM/R)).
How does acceleration due to gravity change from the equator to the poles?
The value of 'g' is minimum at the equator due to the centrifugal force caused by the Earth's rotation and the equatorial bulge, and maximum at the poles.
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