The Universal Law of Gravitation

Isaac Newton deduced that every object in the universe attracts every other object with a force proportional to the product of their masses and inversely proportional to the square of the distance between them. This explains planetary orbits and falling apples alike.

Free Fall, Mass, and Weight

Objects falling under gravity alone are in free fall, experiencing constant acceleration (g = 9.8 m/s²). While an object's mass remains constant everywhere, its weight (the gravitational force acting on it) changes depending on location. For instance, your weight on the moon is about 1/6th of your weight on Earth.

Thrust, Pressure, and Buoyancy

Thrust is force acting perpendicular to a surface, and pressure is thrust per unit area. In fluids, objects experience an upward buoyant force. According to Archimedes' Principle, an immersed object experiences an upward force equal to the weight of the fluid it displaces.