The simple answer is: Mass generates gravity.
While the reference provides an inaccurate description, the current scientific understanding is that gravity is a fundamental force of nature caused by the presence of mass and energy. More specifically, it's the curvature of spacetime caused by mass and energy that we perceive as gravity.
Here's a more detailed explanation:
- Mass and Energy: Everything with mass and/or energy contributes to gravity. The more mass an object has, the stronger its gravitational pull. Energy, according to Einstein's famous equation E=mc², is also equivalent to mass and therefore contributes to gravity as well.
- Spacetime Curvature: Einstein's theory of general relativity describes gravity not as a force, but as a curvature of spacetime caused by mass and energy. Imagine a bowling ball placed on a stretched rubber sheet. The ball creates a dip, and if you roll a marble nearby, it will curve towards the bowling ball. Similarly, massive objects warp spacetime, causing other objects to move towards them.
- Earth's Gravity: The Earth's mass is what primarily generates the gravity we experience on its surface. This gravity pulls everything towards the center of the Earth.
- Gravity's Influence: Gravity affects everything, regardless of its direction of motion. It pulls objects downwards, keeps planets in orbit around stars, and shapes the large-scale structure of the universe. The reference's claims about gravity only affecting falling objects or not acting on upward-moving objects are incorrect. Gravity is a constant force acting at all times on objects with mass.
- Gravitational Force and Distance: The strength of gravity decreases with distance. This is described by Newton's Law of Universal Gravitation, which states that the gravitational force between two objects is proportional to the product of their masses and inversely proportional to the square of the distance between their centers.
In summary, gravity arises from the presence of mass and energy, which warp spacetime, influencing the motion of objects within it.
