# Robot Impossibly Balances a Pencil on its Tip Like a Boss

Let’s try a little at-home science experiment. Grab a pencil–or a pen if you don’t have one handy–and try to balance its point on your fingertip. Chances are that the pencil falls well before you can finish reading this sentence out loud. Why is this feat so difficult for us to accomplish when the skittery-armed robot above seems to do so with ease?

It turns out that the laws of physics are against us. Any top-heavy item balanced on a narrow point must have its center of mass perfectly in line with the point, otherwise gravity will pull that center more and more off balance until the item topples over. A pencil on its point acts as an inverted pendulum, which is about as unsteady an object as you can get. If a perfectly balanced pencil was nudged off center by only 1/10,000th of the width of an atom, say by single air molecules colliding with it, it would fall over.

Here’s a handy visual explanation from Minute Physics:

So how is this robot able to do the seemingly impossible? As the video’s description reveals, the robot uses two Dynamic Vision Sensor (DVS) retinas as its eyes. Rather than capturing frames of redundant information like conventional cameras, the DVS retinas only transmit “the local pixel-level changes caused by movement in a scene.” This reduces the “power, data storage, and computational requirements” required to, in this case, keep the pencil upright, allowing a faster response from the robot’s quick-moving arms. Presumably there’s also integrated software that tells the robot to ignore any horizontal elements in its view or other vertical distractions that are a certain distance away from the area the pencil occupies.

If the balancing act of physics and robotics seems too intense for your DIY science projects, don’t worry; you can actually achieve a perfectly perpendicular pencil on its point by simply changing its center of gravity. There’s a number of ways you can do this, either by using wire and a ball of clay, or wire and some clothes pins. Balancing a pencil on its point is a great way to share some everyday science with the kids at home, win a bar bet, or to show off your smarts in the workplace.

Because science!

Video: Tobi Delbruck, Minute Physics