Definition of Gravity
Gravity in physics is a fundamental force of attraction that acts between all objects with mass. It is the force responsible for keeping planets in orbit around stars, causing objects to fall toward Earth, and governing the large-scale structure of the universe. Unlike other forces, gravity is always attractive and acts over infinite distances, though its strength diminishes with distance.
Key Principles of Gravity
The principles of gravity are encapsulated in Newton's law of universal gravitation, which states that every particle attracts every other particle with a force proportional to the product of their masses and inversely proportional to the square of the distance between them. Einstein's general theory of relativity further refines this by describing gravity not as a force but as the curvature of spacetime caused by mass and energy.
Practical Example: Falling Objects
A practical example is an apple falling from a tree. On Earth, gravity accelerates the apple toward the ground at approximately 9.8 m/s², independent of its mass (as per Galileo's insight). This same principle explains why a feather falls slower in air due to air resistance but would fall at the same rate as a hammer in a vacuum, as demonstrated in Apollo 15 experiments on the Moon.
Importance and Applications
Gravity is crucial for life on Earth, enabling stable orbits that prevent extreme temperature swings and holding atmospheres in place. In applications, it underpins technologies like GPS satellites, which account for relativistic gravitational effects, and space exploration, where understanding orbital mechanics allows precise mission trajectories to other planets.