Recently, in an attempt to visualize that the Gravitational pull of the planet is determined by their density rather than their mass, Japan-based planetary scientist of JAXA (Japan Aerospace Exploration Agency) 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. He previously has made many incredible educational astronomy videos like the one on relative cosmic velocity, that comprehended the speed of things moving in space, and his other famous work includes, demonstration of the rotational rate of different planets. Having to visualize our solar system is an eye-treats for many. Dr. O’Donoghue’s planetary visualizations have helped many people to understand what otherwise would be very complex to comprehend. Because of his immense experience with NASA and JAXA, you don’t have to take these visualizations with a grain of salt.
Using this information, they calculated the time it should take for a freefalling object to strike at the surface of those selected celestial bodies, considering any wind resistance is absent. In addition to major planets, solar system objects considered for the video include Sun, Moon, Ceres, and even Pluto.
According to O’Donoghue, the pull of gravity on bigger planets and earth are different, for example; a ball falling on Saturn will hit the ground in 13.8 seconds, while the one in Uranus will only take 15 seconds. While explaining his animation in a YouTube video, he said,
it might be surprising to see large planets have a pull comparable to smaller ones at the surface.
He goes on to explain the reason behind the difference in the rate of fall saying, “For example, Uranus pulls the ball down slower than at Earth! Why? Because the low average density of Uranus puts the surface far away from the majority of the mass. Similarly, Mars is near twice the mass of Mercury, but you can see the surface gravity is the same… this indicates that Mercury is much denser than Mars.” Interestingly, he also referenced the gravity experiment of Dave Scott – an astronaut, on the Moon. Apollo 15 Commander David Scott dropped a feather and a hammer on the Moon from the similar Hight, simultaneously, and surprisingly, they both landed at the same time. The main reason being, that, if there is no air resistance, all objects will fall at the same time, doesn’t matter how much they weigh.