While an object’s fundamental properties remain constant across different celestial bodies, its apparent heaviness, or weight, varies significantly. This difference is due to the varying gravitational forces on each planet. Understanding this distinction requires defining mass and weight.
What Mass Really Is
Mass represents a fundamental property of matter, quantifying the amount of material an object comprises. It is an intrinsic characteristic, meaning it does not change based on an object’s location or gravitational pull. For instance, a rock contains the same amount of matter whether on Earth, the Moon, or floating in space. Mass also measures an object’s resistance to acceleration, known as inertia; more mass requires more force to change motion.
What Weight Really Is
Weight is a measure of the force exerted on an object due to gravity. This force pulls an object towards the center of a celestial body. Because weight depends directly on the strength of the gravitational field, it changes with location. For example, an object weighs less on the Moon than on Earth because the Moon’s gravitational field is weaker. Weight is expressed in units of force, such as Newtons.
How Gravity Affects Weight
Gravitational force, which determines an object’s weight, is influenced by two primary factors: the mass of the celestial body and the distance from its center. Planets with greater mass generally exert a stronger gravitational pull. However, density and radius also play roles, as gravity weakens exponentially with increased distance from the center of mass. This means a very large but less dense planet might have a surface gravity similar to a smaller, denser one. Gravitational acceleration varies significantly across different planets, directly impacting an object’s weight.
Weight on Other Worlds
An individual weighing 150 pounds (68 kilograms) on Earth would experience significantly different weights across the solar system. On the Moon, with roughly one-sixth of Earth’s gravity, that person would weigh about 25 pounds (11.3 kg). Traveling to Mars, where gravity is about 38% of Earth’s, the same individual would weigh around 57 pounds (26 kg).
On more massive planets, weight increases considerably. On Jupiter, the largest planet, an Earth-bound 150-pound person would weigh approximately 351 pounds (159 kg), experiencing gravity about 2.34 times stronger than Earth’s. Venus, often called Earth’s twin due to its similar size, has a gravitational force about 90% of Earth’s, meaning a 150-pound person would weigh around 135 pounds (61 kg). Even Uranus, despite its large size, has a surface gravity slightly less than Earth’s, resulting in a weight of about 132 pounds (60 kg).