26Comments
Astronaut Alan Shepard famously hit his golf ball a lousy 36 meters (118 feet) on the surface of the moon, and scientists on the International Space Station have even taken to playing baseball while in orbit, although if you’re going to play sports in space then you really should familiarize yourself with the behavior of balls across the solar system. To help us with this, planetary scientist Dr James O’Donoghue has created an animation demonstrating how long it takes a ball to freefall from a height of one kilometer (0.6 miles) on a selection of celestial bodies.
To create the video, O’Donoghue and fellow astronomer Rami Mandow referred to data published by NASA regarding the force of gravity at the equator of each planet in the solar system. This allowed them to calculate the time it would take for an object to fall to the surface of each of these worlds, assuming an absence of any wind resistance.
For example, the force of gravity on Earth causes items to fall at a rate of 9.8 meters (0.0061 miles) per second, which means a one-kilometer (0.6 mile) drop would take 14.3 seconds. Despite being much larger than our home planet, Saturn’s gravitational pull is only slightly stronger, and produces a fall speed of 10.4 meters (0.0065 miles) per second. As such, a ball would take 13.8 seconds to drop to the surface of the ringed gas giant.
“It might be surprising to see large planets have a pull comparable to smaller ones at the surface,” said O’Donoghue on Twitter. “For example Uranus pulls the ball down slower than at Earth! Why? The low average density of Uranus puts the surface far away from the majority of the mass.”
Ultimately it is the density of an object, rather than its mass, that determines the speed at which a ball falls to its surface. This results in some surprising observations across the solar system. For instance, as O’Donoghue explains, “Mars is nearly twice the mass of Mercury, but you can see the surface gravity is actually the same, this indicates that Mercury is much denser than Mars.”
As the animation indicates, ball games are likely to be particularly challenging on the sun, as items in free-fall travel at a staggering 274 meters (0.17 miles) per second on our star, taking just 2.7 seconds to drop to the surface from a height of one kilometer (0.6 miles) (assuming they don’t become vaporized). At the other end of the spectrum is the dwarf planet Ceres, the largest object in the asteroid belt between Mars and Jupiter. A game of volleyball here would likely put most spectators to sleep, given that it takes 84.3 seconds for a ball to gently make its way to the surface.
It’s worth pointing out that the size and mass of the ball is irrelevant, as in the absence of any air resistance all objects fall at the same speed. This was famously demonstrated by Apollo 15 astronaut David Scott, who dropped a hammer and a feather from an equal height on the moon in 1971, confirming that they both reached the ground at the same time.
