In a vacuum, every object accelerates toward Earth at the same rate: roughly 9.8 meters per second squared, regardless of its mass. That means after one second of free fall, something is moving at about 9.8 m/s (around 22 mph); after two seconds, about 19.6 m/s (44 mph); after three, about 29 m/s (65 mph). But almost nothing falls in a vacuum. The moment air gets involved, the answer splits into dozens of different answers depending on shape, size, density, altitude, and even which planet you are on.
The Rule That Surprised Everyone
For roughly two thousand years, the common assumption was that heavier objects fall faster than lighter ones. It feels intuitively right: drop a bowling ball and a feather, and the bowling ball wins every time. But that intuition confuses the effect of air with the effect of gravity itself. Galileo challenged the old view with a clever thought experiment. If a heavy stone falls faster than a light one, what happens when you tie them together? The combined object is heavier, so it should fall faster. But the light stone should also act as a drag on the heavy one, slowing the pair down. You get a contradiction, which means the original assumption is wrong. Modern classroom experiments using high-speed video tracking of simple paper cones have confirmed that every step of Galileo’s argument holds up.
1American Journal of Physics. Using history to foster critical scientific thinking: Aristotle and Galileo’s debate resolved through high-speed motion tracking in the classroomThe formal version of this idea is called the weak equivalence principle: all bodies fall at the same rate in a gravitational field, no matter what they are made of or how much they weigh. This has been tested to extraordinary precision, including in space, where a satellite-based experiment confirmed it with accuracy far beyond anything possible on Earth’s surface.
2Physical Review Letters. Galileo’s free-falling objects experiment passes space test further proving equivalence principleSo in the idealized case, the answer to “how fast does something fall?” is simple math. Multiply 9.8 by the number of seconds it has been falling, and you get its speed. A coin dropped from a tall building would, in a vacuum, be moving at about 140 mph after just four seconds. In practice, that coin never reaches anything close to that speed, because air gets in the way.
Why Air Changes Everything
The instant something starts falling through the atmosphere, it collides with air molecules. Those collisions push back against the object, creating drag. Drag is small at low speeds and grows rapidly as the object speeds up. At some point, the drag force pushing up equals the gravitational force pulling down, and the object stops accelerating. The speed it settles into is called terminal velocity, and it varies wildly from one object to another.
A skydiver falling belly-down reaches a terminal velocity of roughly 120 mph. The same skydiver falling headfirst, arms tucked, can exceed 150 mph because their cross-sectional area facing the wind is smaller. A golf ball’s terminal velocity is around 70 mph. A flat sheet of paper might drift down at just a few miles per hour. The key factors are the object’s weight, its frontal area, and how streamlined its shape is. A dense, compact, smooth object punches through air more easily; a light, wide, rough-surfaced object gets caught up in it.
Altitude matters too. Air is thinner at higher elevations, which means less drag. A skydiver jumping from extreme altitude initially falls through air so thin that the drag is much lower than near the ground. Modeling this realistically requires accounting for air density that changes continuously with altitude, which is why simplified textbook equations often underestimate speeds at the top of a high-altitude fall and overestimate them near the ground.
3Current Problems in Research. Nonlinear Dynamics of Skydiving with Variable Atmospheric Density and Gradual Parachute DeploymentShape Matters More Than Weight
If you had to pick one factor that most determines how fast something falls through air, it would be shape, not mass. Two objects of identical weight can have dramatically different terminal velocities depending on their geometry. A solid steel ball and a crumpled sheet of steel foil weighing exactly the same will fall at very different rates, because the crumpled foil catches far more air.
The physics community quantifies this through something called the drag coefficient, a number that captures how much a particular shape resists moving through a fluid. A smooth sphere has a relatively low drag coefficient. Anything that deviates from a sphere, especially irregular shapes with rough surfaces or protruding features, experiences more drag. Research on irregularly shaped particles has consistently shown that at any given speed, irregular objects experience higher drag than spheres, and that the difference grows as the object moves faster and as its shape departs further from a compact, rounded form.
4Powder Technology. Drag coefficients of irregularly shaped particlesThere is an interesting wrinkle for objects with non-circular cross-sections, like flat plates or elongated rods. These shapes tend to trigger turbulence at lower speeds, which means their drag behavior changes less as they speed up. A sphere’s drag can shift abruptly at certain speeds as its airflow transitions from smooth to turbulent; a flat, angular object’s drag is already dominated by turbulence, so it behaves more predictably across a wider range of speeds.
5Powder Technology. Drag of non-spherical solid particles of regular and irregular shapeRaindrops, Hailstones, and Other Natural Fallers
Rain is a useful case study because water drops come in a wide range of sizes, and their behavior while falling changes with diameter. Very small raindrops, under about one millimeter across, behave like tiny rigid spheres. They fall steadily, maintain a round shape, and reach a terminal velocity of roughly 2 m/s (about 4 mph). Larger drops are a different story. As a raindrop grows beyond one millimeter, the force of air pushing against its underside starts to flatten it, and eventually the drop oscillates and wobbles as it descends. These larger drops also experience more drag than a perfect sphere of the same size would, because of their distorted shape.
6Elsevier (ScienceDirect). Shapes and oscillations of falling raindrops — A reviewThe largest raindrops, around five to six millimeters across, top out at roughly 9 m/s (about 20 mph) before they break apart from aerodynamic stress. So contrary to the common worry that rain falling from miles up in the sky must hit you at terrifying speed, even the biggest drops are moving at a gentle jog’s pace by the time they reach the ground.
Hailstones are a different matter. They are denser than water drops, often irregularly shaped, and can be much larger. The terminal velocity of a hailstone depends heavily on whether you model it as a smooth sphere or account for its actual lumpy shape. When researchers measured natural hailstones rather than idealized spheres, they found that the terminal velocities and kinetic energies were on average lower than those predicted by a simple spherical model, though some irregular shapes could actually fall faster than a sphere of the same maximum diameter.
7Geophysical Research Letters. Terminal velocities and kinetic energies of natural hailstonesA golf-ball-sized hailstone (roughly 4 to 5 cm across) can reach terminal velocities in the neighborhood of 100 mph, which is why severe hail causes serious damage to vehicles, roofs, and anything caught outside. Grapefruit-sized hailstones, rare but documented, can exceed 100 mph and carry enough kinetic energy to crack windshields or injure people.
Seeds That Refuse to Fall Fast
Evolution has produced some of the most elegant falling objects on the planet. Maple samaras are the classic example: winged seeds that autorotate as they descend, spinning like tiny helicopters. This spinning dramatically slows their fall and allows them to be carried horizontally by even light winds, spreading the tree’s offspring far from the parent trunk.
8PubMed Central. Wind Dispersal of Natural and Biomimetic Maple SamarasA maple samara’s terminal velocity is just one to two meters per second, slow enough that a moderate breeze can carry it hundreds of meters. The autorotation creates a stable leading-edge vortex on the wing, which generates lift and keeps the seed aloft much longer than a non-spinning object of similar weight would last. Engineers have studied samaras for biomimetic applications, designing small rotating devices that descend slowly and could serve as air-dropped sensors or monitoring tools. The design principle is simple: convert gravitational energy into rotational motion rather than downward speed, and you fall much more slowly.
Dandelion seeds take a different approach. Their parachute-like pappus creates a separated vortex ring above the seed, generating drag so efficiently that the seed’s terminal velocity can be as low as 0.3 m/s, roughly the speed at which dust motes drift. These biological solutions to falling slowly are far more sophisticated than most human-designed parachutes relative to their scale.
Falling Through Liquid
Everything discussed so far involves falling through air, but objects fall through liquids too, and the physics is the same in principle but very different in practice. Water is roughly 800 times denser than air at sea level, so drag forces are enormously larger. A steel marble that reaches a terminal velocity of dozens of miles per hour in air might settle to just a few centimeters per second in thick honey.
For very small particles falling through viscous fluids, the relationship between size and settling speed is remarkably clean and predictable. Stokes’ law describes how a small sphere sinks through a fluid, and it has been verified down to particles not much larger than some viruses. Researchers confirmed this by measuring the sedimentation rate of latex particles and comparing the calculated diameter against independent measurements from electron microscopy and light scattering, finding excellent agreement.
9Journal of Polymer Science. Studies on the validity of the Einstein viscosity law and Stokes’ law of sedimentationThis principle shows up in countless everyday situations. Sediment settling in a glass of muddy water, cream separating in unhomogenized milk, blood cells settling in a test tube for a sedimentation rate test: all are governed by the same falling-through-fluid physics. The smaller and lighter the particle relative to the fluid, the slower it settles. In extremely viscous fluids like cold tar or thick silicone oil, even fairly heavy objects can take minutes to sink a few centimeters.
Where You Stand on Earth Changes the Answer Slightly
The 9.8 m/s² figure for gravitational acceleration is an average. The actual value at Earth’s surface varies by about half a percent depending on where you are. Gravity is strongest at the poles and weakest near the equator, mainly because Earth is not a perfect sphere (it bulges at the equator, putting you farther from the center) and because the planet’s rotation creates a slight outward centrifugal effect at the equator. Altitude and local geology play roles as well, with dense underground rock formations producing slightly stronger local gravity and the reduced pull at high elevations weakening it.
10Measurement. The effect of gravity acceleration on non-automatic weighing systemsHalf a percent sounds trivial, and for your everyday experience of dropping things, it is. You will never notice the difference between falling in Helsinki and falling in Quito. But it matters for precision instruments. High-accuracy scales used in trade and scientific measurement need to be calibrated to local gravity, or they will give slightly wrong readings. A kilogram of gold weighed on a scale calibrated in Norway would register slightly differently on the same scale moved to Singapore, unless the scale is recalibrated. This is why precision weighing instruments specify the gravitational zone they are calibrated for.
Falling on Other Worlds
The speed at which something falls changes dramatically on other planets and moons, because both surface gravity and atmospheric density vary enormously across the solar system. On the Moon, with about one-sixth of Earth’s gravity and essentially no atmosphere, a dropped object accelerates at roughly 1.6 m/s² and never encounters air resistance. It just keeps speeding up until it hits the ground, but it speeds up much more slowly than on Earth.
Mars has about 38 percent of Earth’s surface gravity, so objects accelerate more slowly. But Mars also has a very thin atmosphere, only about one percent as dense as Earth’s. That thin air provides almost no braking. A comparative study of planetary atmospheres found that Mars’s atmosphere is not enough by itself to slow a descending lander to safe speeds, which is why Mars missions use combinations of heat shields, parachutes, and retrorockets to land safely.
11arXiv. Comparative Study of Planetary Atmospheres and Implications for Atmospheric Entry MissionsVenus presents the opposite problem. Its surface gravity is close to Earth’s, but its atmosphere is crushingly thick, about 90 times denser than ours at the surface. An object falling through Venus’s atmosphere experiences intense deceleration and heating. Titan, Saturn’s largest moon, is perhaps the most interesting case: it has low gravity (about 14 percent of Earth’s) and an atmosphere roughly 50 percent denser than ours at the surface. Falling through Titan’s atmosphere is gentle by solar system standards, with low deceleration and low heating, which is one reason the Huygens probe was able to descend there on a relatively simple parachute system.
11arXiv. Comparative Study of Planetary Atmospheres and Implications for Atmospheric Entry MissionsThe gas giants, Jupiter and Saturn, have enormous gravity wells that accelerate incoming objects to extreme speeds. Entry into Jupiter’s atmosphere involves deceleration forces and heating rates so severe that only heavily shielded probes can survive it. The Galileo atmospheric entry probe, which plunged into Jupiter in 1995, experienced peak deceleration of roughly 230 g’s, a force that would be instantly fatal to a human and destructive to most equipment.
When Objects Fall from Space
Meteoroids entering Earth’s atmosphere represent one of the most dramatic versions of the falling question. A meteoroid does not start from rest like a dropped ball. It enters the atmosphere at speeds typically between 11 and 72 kilometers per second, which is many times faster than any bullet. At these speeds, the air in front of the object cannot move out of the way fast enough and compresses violently, heating the meteoroid’s surface to thousands of degrees and causing it to glow. This is the “shooting star” phase.
Most meteoroids burn up entirely during this fiery deceleration. Those that survive long enough to slow below about 3 km/s enter what researchers call “dark flight,” where the meteoroid is no longer glowing and is decelerating through progressively thicker air. During dark flight, the conditions shift from supersonic to subsonic, and eventually the fragment reaches terminal velocity and falls like any other rock, typically at speeds between 200 and 400 mph depending on its size and shape.
12The Planetary Science Journal. Dark-flight Estimates of Meteorite Fall Positions: Issues and a Case Study Using the Murrili Meteorite FallBy the time a surviving meteorite reaches the ground, it has often been falling slowly enough for long enough that its surface is no longer hot. Small meteorites recovered shortly after impact are sometimes barely warm to the touch, which surprises people who imagine them as glowing embers. The intense heating happens high in the atmosphere at hypersonic speeds; the final miles of descent at terminal velocity allow the fragment to cool considerably.
Microgravity and Controlled Free Fall
Scientists sometimes need to study what happens when things fall freely without air resistance, not in distant space, but right here on Earth. Drop towers are facilities where experiments are released into free fall inside evacuated or near-evacuated shafts, creating brief periods of near-weightlessness. The object and everything inside it are all falling together, so from the experiment’s perspective, gravity has effectively disappeared.
Modern drop towers have been upgraded with active drive systems capable of launching payloads upward and catching them on the way down, effectively doubling the microgravity time. Some of these facilities can handle payloads of up to 1,000 kilograms and offer high repetition rates, which makes repeated experiments affordable compared to launching something into orbit.
13ScienceDirect (Elsevier / Advances in Space Research). Novel active driven drop tower facility for microgravity experiments investigating production technologies on the example of substrate-free additive manufacturingThese controlled-fall environments have been used to study everything from combustion behavior without buoyancy-driven convection to how molten metal solidifies when it is not being pulled in any direction. They also serve as test beds for manufacturing techniques that could eventually be used in space, such as additive manufacturing in zero gravity, where understanding how materials behave without a consistent “down” direction is critical.
Braking Systems Inspired by Falling
Understanding how fast things fall has practical safety implications that go well beyond physics curiosity. Elevator safety systems, for example, must be designed to catch a falling car and bring it to a stop without injuring passengers. One approach uses eddy-current magnetic brakes, which generate a braking force proportional to the speed of the falling object. These systems work without physical contact between braking surfaces, which means they do not wear out the way friction brakes do and can serve as reliable backup deceleration systems for elevators and guided rail transportation.
14Transactions of the Canadian Society for Mechanical Engineering. THE DESIGN OF EDDY-CURRENT MAGNET BRAKESThe engineering challenge is that a falling elevator accelerates at nearly 9.8 m/s² if its cables snap, meaning it can reach dangerous speeds within seconds. A car in a 30-story building could theoretically reach roughly 50 mph in less than four seconds of free fall. Magnetic braking systems that engage automatically based on speed provide a failsafe layer that works even if mechanical systems fail, precisely because the braking force increases as the fall gets faster. The same principle has been adapted for amusement park rides, industrial lifting equipment, and experimental rail systems where reliable, maintenance-free deceleration matters.