The Reverse-Threaded Pedals

Cyclists who work on their bikes will eventually notice that removing both pedals is frustrating and weird. It turns out the left pedal on a bicycle has a reverse (left-hand) thread. This means you have to screw it “backwards”. WTF, WHY? Turns out, the pedals are designed to stay tight because of a phenomenon called mechanical precession.

Why One Pedal is Reverse-Threaded (Mechanical Precession)

Mechanical precession is the effect that keeps your pedals secured. In simple terms, when a round object (like a pedal spindle) is forced against the threads in a rotating manner, it will tend to slowly roll around in the opposite direction of that rotation. This means that even though the left pedal rotates forward (which would normally unscrew a right-hand thread), the precession effect makes it tighten instead. In fact, the torque from mechanical precession is much greater than any loosening force from the pedal’s bearings. In nearly all bikes since the 1930s, manufacturers solved loose pedals by using a left-hand thread on the left side.

Pressure Cookers: Sealed Chambers That Harness Physics for Faster Cooking

Introduction

In kitchens around the world, a hissing pot on the stove signals something magical. Pressure cookers—whether classic stovetop models or modern multi‑cookers—promise to transform tough cuts of meat into tender stews and dried beans into velvety soups in a fraction of the time. But how do they do it? The answer combines thermodynamics, the ideal gas law and a centuries‑old invention that turned steam into a household tool. This article peels back the lid on pressure cookers, explaining how they raise the boiling point of water, tracing their history from Denis Papin’s “steam digester” to the Instant Pot, and exploring modern innovations that extend their capabilities beyond cooking.