Cornell professor Andy Ruina showed how two falling chain ladders behave differently in a viral physics experiment. While one ladder falls freely, the other hits a table, causing its rungs to pull down in a strange way. The video explained that contact forces and torque change how objects move.
Physics has long held the power to challenge what appears obvious to the human eye. A falling object, for instance, ought to follow the familiar course of gravity. Yet a demonstration by Andy Ruina, former professor of mechanical engineering at Cornell University and currently a Visiting Professor at Plaksha University, offers a reason to look twice.
The experiment, featured in a video published by Veritasium, places two chain ladders in motion at precisely the same time. What follows is a demonstration of mechanics that turns an ordinary fall into a question worth examining.
THE FALLING LADDER EXPERIMENT
The arrangement is simple. Two chain ladders are suspended side by side and released together. On one side, the ladder is allowed to fall freely towards the ground. On the other, a table is placed in its path, so that the falling ladder strikes its surface before reaching the ground.
At first, one might expect the two to behave alike. Both are released at the same moment, and gravity acts upon them. But the moment the first ladder meets the table, the experiment takes a different course.
The ladder striking the table does not simply stop as a single rigid object would. Its individual rungs make contact with the surface in succession. As each rung strikes, the contact produces a force that acts upon the remaining portion of the chain. The upper rungs are pulled down as the lower ones meet the table.
This is the source of the curious motion. The chain ladder continues to change its shape as it falls, and the interaction between its rungs and the table alters the movement of the sections still in the air.
THE PHYSICS BEHIND THE FALL
The demonstration concerns the principles of Newtonian mechanics, particularly force, torque and rotational motion. It is not a simple illustration of one isolated law of gravity.
When a rung strikes the table, the contact force can produce a turning effect, known as torque. This affects the motion of the rung and the chain connected to it. The successive contacts make the ladder behave differently from an object in uninterrupted free fall.
Ruina's experiment thus brings attention to a point often overlooked in elementary explanations of falling bodies: the manner in which an object is connected, supported and brought into contact with another surface matters.
The video, titled Falling Ladders – Why Does This Happen?, was published on Veritasium's YouTube channel in January 2023. Its central question is a plain one: which ladder falls faster, the one in free fall or the one that strikes the table?
The answer lies not in gravity alone, but in the mechanics of the falling chain.
A table, two ladders and a moment of observation are enough to show that even a familiar law of nature may have more to teach when examined with care.