What if you tried to swing in space?

Wheee! You swing up high. Then you swing back down.

Something pulls you back every time. What if that pull was gone? Could you still swing?

Pull a swing back and let go, and it swoops down, rises up the other side, and comes back again. Physicists call anything that swings like this a pendulum: OpenStax, a physics textbook, even uses a child's swing as an example.

But what keeps it going back and forth? And what would a swing do with no pull at all? NASA says small amounts of gravity are everywhere in space, but in this lab you can switch gravity off in a model and find out.

A playground swing is a pendulum: a mass hanging from a pivot that oscillates about its lowest point. For small swings, OpenStax notes, a pendulum is a simple harmonic oscillator whose period depends only on its length and the acceleration due to gravity.

This lab asks what supplies the restoring force, and what happens when it is removed. The model swings a seat on 2 m ropes, released from rest at 20°, on Earth, on the Moon, on Mars, at Jupiter's cloud-top gravity, and in an imaginary world with no gravity at all.

On Earth, the swing goes down, up, down, up.

It goes there and back in about three seconds. Then it does it again!

In the model, a swing with ropes 2 meters long, pulled back and let go, takes about 2.9 seconds to swing over and back. That is about 21 swings every minute, and the seat zooms through the bottom at about 1.5 meters per second.

On the way down it speeds up. On the way up the other side it slows down, stops for a moment at the top, and then falls back. Gravity is doing all of that.

With L = 2 m, a 20° release and g = 9.81 m/s², the model's exact undamped period is 2.859 s (the small-swing formula gives 2.837 s), with 21.0 swings per minute and a bottom speed of √(2gL(1 − cos θ₀)) = 1.54 m/s.

At every point gravity's pull along the arc points back toward the bottom, accelerating the seat down and decelerating it on the way up. With no damping, energy simply swaps between height and speed, and the swing repeats forever.

Olly turns gravity off in the pretend lab. He pulls the swing back and lets go.

The swing does not move! Nothing pulls it down. It just stays there.

Now set gravity to zero and let the seat go from the same spot. In the model, nothing happens at all. The seat stays exactly where you let it go, tipped to one side, because nothing pulls it toward the bottom.

Try the other worlds too. On the Moon, the same swing takes about 7 seconds to go over and back, a slow, floaty ride. On Mars it takes about 4.6 seconds. At Jupiter's strong pull it takes only about 1.8 seconds.

With g = 0 the model's equation reduces to θ″ = 0. Released from rest, the seat stays at 20° indefinitely; the period is undefined (no restoring force) and the bottom speed is zero. The model ends such runs after 6 s.

Across real gravities, T scales as g^(−1/2): 7.035 s on the Moon (1.62 m/s²), 4.649 s on Mars (the model's 3.71; NASA's fact sheet gives a mean of 3.73), 2.859 s on Earth and 1.759 s at Jupiter's 1 bar level (25.92, NASA's mean). Sixteen times Jupiter's pull over the Moon's gives a period ratio of about four.

Gravity always pulls the seat down toward the bottom.

So the seat falls, then swings up, then falls again. No pull means no falling, and no swinging.

A swing is always trying to fall. Pulled to one side, gravity tugs the seat toward the lowest point. It overshoots, rises up the other side, and gravity tugs it back again. That back-and-forth tug is what makes the swinging.

Weaker gravity tugs more gently, so the seat speeds up more slowly and each swing takes longer. With no gravity there is no tug, so a still seat stays still. Our model is simple: the ropes are a stiff, weightless rod and the seat is a single point.

The net force along the arc, −mg sin θ, is a restoring force: it always points toward equilibrium and grows with displacement, which is what makes oscillation possible. The angular frequency √(g/L) comes directly from g, so g = 0 removes oscillation entirely, not just slows it.

Model limits: a point mass on a rigid weightless rod (real ropes go slack when the seat rises above the pivot, and a rider is not a point), damping only if you add it, and released from rest only, so the model cannot show what a push would do without gravity.

Astronauts float in their space station. Gravity is still there! They float because everything is falling around Earth together.

So a swing might not swing back down there either.

NASA explains that the International Space Station orbits about 200 to 250 miles above Earth, where gravity is still strong: someone who weighs 100 pounds on the ground would weigh 90 pounds there. Astronauts float because the station and everything in it are falling around Earth together.

That gives scientists an idea: if a swing were set up inside the station, the seat and its frame would be falling together, so the seat might not be pulled toward the bottom at all. Like our no-gravity model, it might not swing back. NASA adds that a spacecraft far enough from Earth would feel very little gravity at all.

NASA's microgravity explainer notes that at the station's 200–250 mile altitude, gravity is still about 90% of its surface value; the crew float because the station and its contents are in free fall together. Relative to the cabin, nothing accelerates toward the floor.

It follows, as an idea rather than a measurement, that a pendulum attached to the station might have no restoring force relative to its frame: released from rest, its bob might stay put, much as in this lab's g = 0 world. NASA also notes that gravity weakens with distance, so a craft far from Earth would feel very little; there, gravity would be weak, not switched off.