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The Myth of No Gravity in Space

The idea that there's "no gravity in space" is a pervasive misconception that many people hold. It's likely fueled by images of astronauts floating freely in space stations and spacecraft, seemingly uninhibited by gravity.


This image is both awe-inspiring and misleading. When people see astronauts floating around in the International Space Station (ISS), the first thought is often that they are in a "zero-gravity" environment. It looks like a convincing argument for the absence of gravity, doesn't it?

The Truth About Gravity

Contrary to popular belief, gravity is not just a phenomenon confined to Earth or other celestial bodies. In fact, gravity is the force that governs the motion of all objects in the universe. It is the reason why planets orbit around stars, and why moons orbit around planets. According to Newton's law of universal gravitation, every mass attracts every other mass in the universe, and this force of attraction is what we call gravity. The formula for gravitational force is F = G (m1*m2) / (r^2), where F is the gravitational force, G is the gravitational constant, m1 and m2 are the masses of the objects, and r is the distance between their centers.

Zero-Gravity Experience

The Fallacy of "Zero Gravity"

When astronauts are floating in a spacecraft orbiting Earth, they are not devoid of gravity. In fact, the gravitational pull at the altitude of the ISS is about 90% of what it is on the Earth's surface. So why do astronauts float?

The answer is simple: they are in freefall, just like the spacecraft they are in. Imagine you're in a falling elevator; you would feel weightless because both you and the elevator are accelerating towards the Earth at the same rate due to gravity. In the case of the ISS, it's moving forward at a high speed while also being pulled towards Earth by gravity. The result is a stable orbit, where the spacecraft's forward motion balances out the gravitational pull, leading to a state of continuous freefall for both the ISS and its occupants.

Thought Experiments

To help understand this complex topic, let's delve into some thought experiments and real-world examples.

Newton's Cannonball

Thought Experiment 1: Newton's Cannonball

Imagine firing a cannonball horizontally from a tall mountain. If you fire it with a low initial speed, it will land some distance away. Increase the speed, and it lands farther away. Now, if you fire the cannonball with sufficient speed (ignoring air resistance), it would circle the Earth indefinitely. This is essentially what an orbit is—a continuous fall around Earth.

Thought Experiment 2: The Car on a Curved Road

Picture a car driving at high speed on a circular track that suddenly becomes frictionless. The car would naturally tend to move in a straight line (Newton’s First Law), but gravity pulls it towards the center of the circle. The car doesn't crash or fly off but stays on the curved path, continuously "falling" around the curve. This mimics what happens in orbit but in a more relatable, two-dimensional scenario.


Example: Satellites

Satellites are prime examples of how gravity works in space. They are launched at high speeds, typically at velocities of about 28,000 km/h for geostationary orbits, to counterbalance Earth's gravity. This velocity ensures that their inward gravitational pull is balanced by their outward inertia, thus sustaining an orbit.

The Role of Gravity in Cosmic Structures

Gravity is also responsible for the formation and stability of galaxies, star systems, and even the clusters of galaxies. Its influence extends over vast distances in space, holding celestial objects together. The gravity from our Sun holds Earth in orbit, just as the mutual gravitational attraction between galaxies in a cluster keeps them from flying apart.

The Influence of Gravity Beyond Earth Gravity isn’t just a localized Earth phenomenon; its effects stretch across the entire universe. Let’s consider some real-world examples that extend beyond our planet.


Black Holes: Extreme Gravity

Black holes are extreme examples of how gravity works at cosmic scales. They are formed when a massive star collapses under its own gravity, creating a region in space where gravity is so intense that not even light can escape. This demonstrates the universality and potency of gravitational forces, acting across different scales and conditions.

Gravitational Waves: A New Perspective

The discovery of gravitational waves has provided a novel way to observe the universe. These are ripples in spacetime created by the acceleration of massive objects, like merging black holes or neutron stars. Einstein predicted them over a century ago, and their recent detection confirms that gravity has far-reaching implications, affecting the very fabric of spacetime.

The Solar System: A Balancing Act

Our own solar system is a textbook example of gravity at work. The Sun's gravity holds the planets in their orbits, while each planet’s gravity affects its moons. It’s a complex interplay of gravitational forces that has been stable for billions of years. Take Jupiter and its moon Io, for example. Io experiences massive tidal forces due to Jupiter’s gravity, which make it the most geologically active body in the solar system. This demonstrates how the same force responsible for an apple falling from a tree on Earth can influence moons and planets millions of miles away.

Implications for Space Exploration

The Role of Gravity in Space Missions

Understanding gravity is essential for space exploration. For example, spacecraft use “gravity assists” from planets to gain speed or change direction without using fuel. This involves flying close to a planet and “borrowing” some of its orbital energy. Engineers and scientists, especially those specializing in spacecraft dynamics and control systems, use complex algorithms to calculate these maneuvers accurately.

The Challenge of Artificial Gravity

Creating a stable artificial gravity environment in a spacecraft remains a challenge. Research into rotating habitats and other novel solutions aims to tackle the health issues astronauts face in microgravity, such as muscle atrophy and bone density loss. This research hinges on a deep understanding of how gravity works.

Future Research

The ongoing study of gravitational interactions, both at quantum levels and cosmic scales, may pave the way for groundbreaking technologies and a deeper understanding of the universe. Research into gravity is not just an academic exercise but has practical implications ranging from satellite design to potential interstellar travel.

Gravity is an all-encompassing force that acts not only on Earth but also throughout the universe. The idea that there's no gravity in space is a simplification that does a disservice to this fundamental force and its complexity. By understanding how gravity really works, we can better appreciate the natural phenomena around us, make advancements in space technology, and deepen our knowledge of the universe. Whether it's keeping satellites in orbit or governing the dynamics of distant galaxies, gravity is everywhere, making its presence known in both subtle and profound ways.

Cite this article as: Kumar, Yajur “The Myth of No Gravity in Space” Space Navigators, 2 September 2023, ""


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