Ch 7Gravitation — Class 11 Physics, concept-first.

For most of human history, the motion of the planets, the Moon and the Sun across the sky was described only in terms of how they appeared to move, without any single physical principle explaining why…

Johannes Kepler analysed decades of the astronomer Tycho Brahe's painstakingly accurate naked-eye observations of the planet Mars and, from them, worked out three precise geometrical laws that every p…

Newton's universal law of gravitation states: every particle of matter in the universe attracts every other particle with a force whose magnitude is directly proportional to the product of their two m…

The constant appearing in Newton's law of gravitation, , is called the universal gravitational constant. Its currently accepted value is

Consider an object of mass resting at the Earth's surface, a distance (the Earth's own radius) from the Earth's centre, and treat the Earth, for this purpose, as though its entire mass were concentrat…

Variation with altitude. Consider a point at height above the Earth's surface, so that its distance from the Earth's centre is rather than . Applying at this new distance,

The Earth spins on its own axis once approximately every hours, and this rotation provides a third reason -- entirely separate from altitude or depth -- why the acceleration due to gravity actually me…

Near the Earth's surface, over small height changes , the gravitational potential energy gained by a mass is given by the familiar formula (measured relative to the ground, at ), because itself can sa…

Gravitational potential at a point in a gravitational field is defined as the gravitational potential energy PER UNIT MASS that a small test mass would have if placed at that point:

Escape velocity is defined as the minimum speed with which an object must be launched from a planet's surface, straight upward (with no further propulsion after launch, and ignoring air resistance), s…

Consider a satellite of mass moving in a circular orbit of radius (measured from the Earth's centre) around the Earth.

A satellite in a circular orbit of radius possesses both kinetic energy (from its orbital motion) and gravitational potential energy (from its position in the Earth's gravitational field); adding the…

A geostationary satellite is an Earth satellite that appears completely stationary in the sky when viewed from any fixed point on the ground -- an enormously useful property for communication and weat…

This chapter built up WBCHSE Unit 6's account of gravitation in the order the syllabus lists it. Kepler's three laws (Section 7.2) described planetary motion purely geometrically -- elliptical orbits…

Sample papers and previous-year board questions for this subject.