If There Is No Gravity In Space, Why Don’t Things Bump Into Each Other?

In space, there is a thing called microgravity, which is a very weak gravitational force. Every object that has mass generates gravity, and gravity causes every object to pull every other object towards it. However, as you travel further away from an object in space, the force decreases. This is why things in space don’t bump into each other.

If you take any two objects, let’s say a shoe and a ball, and release them from a certain height, what will happen? No, this is not a trick question. They will both fall to the ground. Now, you might think that was a dumb question, but be patient. Instead of being on Earth, imagine doing the same thing in space… what will be the outcome? The two objects will float, right? Can you think of a reason for that?

If you answered that on Earth the objects fall due to gravity, but in space they don’t because there is no gravity, then I’m afraid your answer is far from the truth. Every nook and cranny of the universe is filled with myths and mysteries, and the absence of gravity in space is no exception. It is true that space is a partial vacuum devoid of what we commonly call “atmosphere”, but the belief that it is also devoid of forces is a fallacy. In the absence of gravity, how can celestial bodies have defined orbits?

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Space Has Microgravity

In space, gravitational forces do exist. Space has microgravity which is very weak gravitational force. Any object that has mass generates gravity, and gravity causes every object to pull every other object towards it. Space contains massive objects that exert a gravitational force on everything around them. For example, the gravitational pull exerted by the Sun on the entire solar system is what keeps them in orbit, just as Earth’s gravity keeps the moon in orbit. However, as you travel further away from an object in space, the force decreases. This can be explained by Newton’s Universal Law of Gravitation, which states that the G-force between two objects is directly proportional to the combined mass of the objects and inversely proportional to the squared distance between the objects.

Hence, as we move away from the Earth and further into space, the distance increases so the force decreases.

However, if objects in space attract each other, such as the earth and the moon, then how do they not crash into each other? Also, microgravity does not explain astronauts floating in space.

Free Falling In Space

Well, the reason that celestial bodies and our international space station do not suddenly fall out of the sky is because all objects are actually falling. In the case of planets and moons, they have momentum that drives them horizontally, but the gravitational pull is what gives them their curved orbits. Similarly, in the case of an individual astronaut in space or an international space station, they are falling AROUND Earth. What that means is that the space station, all its equipment and astronauts are constantly falling towards Earth.

However, don’t worry, because the space station is also traveling at a speed of 28 thousand km/hr, which roughly matches the way the Earth’s surface curves. When you throw a ball, it does not fall immediately to the ground, right? It follows a trajectory that gradually slopes towards the ground.

Similarly, the space station keeps falling towards the ground, but as it reaches close, the Earth curves beneath it. The ISS falls in a curved path, and the Earth’s surface is curved too, so the former never actually reaches the latter. Also, in space, heavy objects and light objects will fall at equal speeds, irrespective of their mass. Therefore, an astronaut and a spacecraft would both fall at the same speed. This falling without huge amounts of gravity make the astronauts feel weightless and appear to us as though they are floating around.

Isn’t our universe full of surprises? And all this time you thought that science wasn’t magic!

Why Astronauts On The ISS Float Around Weightless

If you’ve ever watched footage of astronauts on the International Space Station, you’ve probably wondered the same thing most people do: have they somehow climbed high enough to escape Earth’s gravity? In a recent ScienceABC poll, more than a third of readers picked exactly that answer — that the ISS crew floats because they’ve flown beyond gravity’s reach. It’s an intuitive guess, and it’s also wrong.

Here’s the surprising truth: the astronauts on the ISS are not weightless because gravity isn’t there. Gravity is very much there, and it’s very nearly as strong up there as it is in your living room. They float because they — along with the entire 420-tonne space station around them — are continuously falling toward Earth. They simply never hit the ground, because the station is also moving sideways fast enough to keep missing it.

That single idea — that the ISS and its crew are in a state of perpetual free fall rather than a state of no gravity — is the key. Everything strange about weightlessness in orbit follows from it.

How Strong Is Gravity At 400 km? (Spoiler: Almost As Strong As Here)

The ISS orbits at an average altitude of about 400 km (250 miles) above Earth’s surface. That sounds like a long way up — and it is, by airliner standards — but it’s peanuts compared to the size of the Earth itself, which has a radius of roughly 6,371 km.

Newton’s universal law of gravitation tells us that the strength of gravity drops off with the square of distance from the center of a massive body. Plug the numbers in: at 400 km up, you are at a distance of 6,771 km from Earth’s center instead of 6,371. The ratio of gravitational pull there to the pull at Earth’s surface works out to (6371 / 6771)² ≈ 0.886 — about 89 percent.

In plain English: according to NASA, a 100-pound person on Earth would weigh about 90 pounds at the altitude of the ISS — if you could stand them on a scale up there. So the astronauts aren’t somewhere gravity-free. They’re only about ten percent lighter than they’d be on the ground. The reason they appear weightless on a scale is that the scale is falling at exactly the same rate they are, so it never has anything to push against.

This is why scientists call the environment on the ISS microgravity, not zero gravity. The “micro” doesn’t refer to the gravitational pull from Earth (which is huge), but to the tiny apparent forces between objects that happen to be falling together inside a falling spacecraft.

Newton's Cannon: The Thought Experiment That Explains Orbits

If gravity is still pulling the ISS down hard, why doesn’t it crash? The cleanest answer was sketched out by Isaac Newton more than three centuries ago, and it remains the easiest way to wrap your head around what an orbit really is.

In a book published posthumously in 1728, A Treatise of the System of the World, Newton imagined standing on top of a very tall mountain and firing a cannonball horizontally. Forget air resistance for the moment. What happens?

• Fire the cannonball gently and it curves downward and lands a few hundred meters away.
• Fire it harder and it lands much farther — its curving trajectory matches more of Earth’s curvature before hitting the ground.
• Fire it hard enough, and as it falls, the Earth’s surface curves away beneath it at exactly the same rate. The cannonball never reaches the ground. It’s in orbit.

This is precisely the situation the ISS is in. The station is going about 28,000 km/h (17,500 mph) sideways relative to Earth’s surface — roughly five miles every second. At that speed, the distance the ISS falls in any given second is matched by how much the curved Earth drops away beneath it. It is literally falling around the planet, completing one full orbit every 90 minutes and racking up sixteen sunrises and sunsets every day.

The same idea explains the moon, communications satellites, GPS satellites, and — taken to a larger scale — even the Earth’s orbit around the Sun. Everything in orbit is just something that has been thrown sideways fast enough to keep missing what it’s falling toward. A peer-reviewed analysis of the cannonball thought experiment, published in the American Journal of Physics, walks through the math in considerably more depth, but the geometric intuition is exactly the one Newton gave us in 1728.

Does The ISS Spin To Cancel Gravity? (Myth-Bust)

There is one final misconception worth dismantling: the idea that the ISS spins fast enough to “cancel” gravity. About one in eight readers in our poll picked that answer. It’s a reasonable guess if you’ve seen sci-fi space habitats from 2001: A Space Odyssey, Interstellar, or The Expanse, where giant ring-shaped stations rotate to give their crews a feeling of weight. The ISS doesn’t do this. Spinning isn’t how it manages microgravity — orbital free fall is.

The mix-up is understandable, because rotation can create artificial gravity, just in the opposite way. If you spin a space station fast enough, the floor of the ring pushes outward against your feet (centripetal force), and that push feels indistinguishable from real gravity. This is the principle behind every proposed rotating space habitat. The ISS, however, is far too small and structurally unsuited to spin for this purpose; the centripetal force on a station that small would be negligible even at high spin rates, and the whole structure would tear itself apart long before reaching a useful figure.

What the ISS does do is maintain a fixed orientation relative to Earth — its “floor” always faces the planet — which means that over the course of one 90-minute orbit, the station completes one slow rotation as seen from the stars. That rotation has nothing to do with weightlessness, though. It’s for keeping antennas pointed at ground stations, solar panels angled at the Sun, and the radiator panels working efficiently. The astronauts inside would still float around weightlessly whether the station rotated or not, because the deciding factor is the free fall, not the spin.

If you’d like to feel a tiny taste of this on Earth, you can — momentarily. The same effect is reproduced by NASA’s parabolic flights (the famous “Vomit Comet”) and even by a free-falling elevator, as Einstein realized in his happiest thought. For the few seconds the aircraft is on the falling arc of its parabola, everyone inside is in free fall — and gravity, while undiminished, becomes invisible.