Gravity is the fundamental mechanism that governs the universe, dictating everything from the orbits of planets to the simple act of standing on a surface. This invisible pull is universal, yet its strength varies dramatically between celestial bodies. Comparing the gravitational pull of Earth with that of the Moon reveals a profound difference in physical experience. This disparity is a direct consequence of their distinct physical properties, requiring a look at the underlying physics that determines how strongly any object attracts another.
Understanding the Mechanics of Gravity
The strength of gravity is determined by Sir Isaac Newton’s Law of Universal Gravitation. This law states that every particle of matter attracts every other particle with a force dependent on two primary factors. The first is the mass of the objects involved; the more massive an object is, the greater its gravitational influence.
The second factor is the distance separating the objects, measured from their centers. Gravitational force weakens rapidly as this distance increases, following an inverse square law. For a person standing on a planet’s surface, this distance is essentially the planet’s radius. The final gravitational force felt on the surface combines these two variables: the total mass of the planet and the distance from the center to the surface.
Calculating the Gravitational Disparity
The difference in gravity between Earth and the Moon results from a massive imbalance in both mass and radius. Earth is significantly more massive than the Moon, holding approximately 81 times more matter. This tremendous difference in mass is the main reason Earth’s gravity is far stronger.
The Moon is also much smaller in size, having a radius about 3.7 times less than Earth’s. This smaller radius means a person standing on the lunar surface is much closer to the Moon’s center of mass. Since gravity increases with the inverse square of the distance, this smaller radius serves to slightly increase the Moon’s surface gravity.
The combined effect of the Moon’s much smaller mass and its modestly smaller radius results in a surface gravity that is approximately 16.6% of Earth’s. This ratio is often simplified to state that the Moon’s gravity is roughly one-sixth that of Earth’s. Specifically, the acceleration due to gravity on Earth’s surface is about 9.8 meters per second squared, while the Moon’s surface gravity is only around 1.625 meters per second squared.
Real-World Effects of Lunar Gravity
The difference in gravitational strength has immediate and observable consequences for objects and humans on the Moon. One noticeable effect is the change in weight, which is the measure of the gravitational force exerted on an object’s mass. A person’s mass remains constant whether on Earth or the Moon. However, since the gravitational pull is only one-sixth as strong, a person who weighs 180 pounds on Earth would register only about 30 pounds on the Moon.
This lower force dramatically alters movement, allowing astronauts to move with a distinct bounding or hopping gait. The reduced gravity allows for higher jumps and longer hang times. Specialized studies have been conducted to understand how the human body adapts to this environment over time.
The Moon’s weak gravitational field also explains its lack of a substantial atmosphere. Unlike Earth, whose strong gravity holds onto a thick blanket of gas molecules, the Moon’s low gravitational pull is insufficient to retain an atmosphere over long periods. Gas molecules easily reach the low escape velocity necessary to drift away into space. This results in the Moon’s airless environment, requiring astronauts to wear pressurized suits for survival.