What if gravity doubled?

When you let go of a ball, it falls. Gravity pulls it down.

What if gravity pulled twice as hard? Would the ball fall twice as fast?

Every time you drop something, gravity pulls it toward the ground. On Earth that pull is the same for a spoon, a shoe or a pumpkin, as long as the air doesn't get in the way.

Now imagine the pull were twice as strong. Would a dropped ball land in half the time? Would it hit the ground twice as hard? In this lab you can double gravity in a model and measure what really changes.

Near Earth's surface, gravity gives every falling object the same acceleration, g ≈ 9.81 m/s², whatever its mass, as long as air resistance is negligible.

This lab asks a deceptively simple question: if g were doubled to 19.62 m/s², how would the fall time and the landing speed change? The tempting answer, "everything doubles or halves", turns out to be wrong, and the reason is hidden in the equations of motion.

On Earth, a falling ball goes faster and faster.

Dropped from 10 meters up, it lands in about one and a half seconds.

On Earth, a dropped ball gains about 9.8 meters per second of speed every second it falls. That steady speeding up is called acceleration.

In our model, with no air in the way, a ball dropped from 10 meters lands after about 1.4 seconds. By then it is moving at about 14 meters per second.

With air resistance neglected, a ball dropped from rest at height h lands after t = √(2h/g) at speed v = √(2gh). From 10 m on Earth that gives t ≈ 1.43 s and v ≈ 14.0 m/s.

The ball's speed grows linearly with time (v = g·t) while the distance fallen grows with the square of time (½g·t²). That square is why the last part of the drop goes by so quickly.

Olly makes gravity twice as strong. The ball drops again.

Now it zooms down faster and lands sooner. It hits the ground harder too!

Set gravity to 19.62 in the model: twice Earth's pull. The same 10-meter drop now takes only about 1 second instead of 1.4, and the ball lands at about 20 meters per second instead of 14.

Notice something surprising. The ball does not land in half the time, and it does not hit twice as fast. Both numbers change by a smaller amount, about 1.4 times. Try other heights and see if that pattern holds.

With g = 19.62 m/s², the 10 m drop takes t = √(2·10/19.62) ≈ 1.01 s and ends at v = √(2·19.62·10) ≈ 19.8 m/s. Because t ∝ 1/√g and v ∝ √g, doubling g shortens the fall by a factor of √2 ≈ 1.41 and raises the impact speed by the same factor.

A neat consequence: landing at 19.8 m/s from 10 m in double gravity is exactly what a 20 m drop gives on Earth. Doubling g has the same effect on impact speed as doubling the height.

A stronger pull speeds the ball up faster.

But the ball spends less time falling. So it does not get twice as fast.

Gravity's pull decides how quickly a falling ball speeds up. Double the pull and the ball gains speed twice as fast every second.

But there is a catch: because it speeds up so quickly, the ball reaches the ground sooner, so it has less time to keep speeding up. The two effects partly cancel, which is why the landing speed grows by about 1.4 times instead of 2.

Our model keeps things simple: no air, no bounce, and a ball that doesn't spin.

Newton's second law gives a = F/m = mg/m = g, so g sets the acceleration directly. The kinematics then fix the rest: a larger acceleration acts for a shorter time, and t = √(2h/g) and v = g·t = √(2gh) carry the square roots.

An energy view gives the same result: the ball's kinetic energy ½mv² equals the work done by gravity, mgh, so v² ∝ g. The model assumes uniform gravity, no drag (switch air on to explore drag), a rigid non-spinning ball and no bounce. It says nothing about how living things or planets would cope with stronger gravity.

Some planets pull harder than Earth. Jupiter is a giant planet.

At Jupiter's cloud tops, the pull is more than twice as strong as on Earth.

Gravity is not the same everywhere in our solar system. The Moon pulls about one sixth as hard as Earth. Giant Jupiter pulls much harder: at the level of its cloud tops, its gravity is about two and a half times Earth's, though Jupiter has no solid ground to stand on.

In a world with double gravity, everything would weigh twice as much. Lifting your backpack would feel like lifting two backpacks. How plants, animals and people would cope is an idea to think about, not something our model shows.

NASA's Jupiter fact sheet gives a mean gravity of 25.92 m/s² at the 1-bar pressure level, about 2.6 times Earth's 9.82 m/s², falling to an effective 23.12 m/s² at the equator because of Jupiter's rapid spin. The Moon's surface gravity is about 1.62 m/s².

A doubled g would double every weight (W = mg). The wider consequences, for muscles, hearts, trees, the atmosphere's thickness or the shape of mountains, are ideas that scientists can reason about but that this simple fall model cannot calculate.