Why your toothpaste refuses to move until you squeeze it
In short: Most liquids flow the moment you apply pressure. But certain materials, known as Bingham plastics, act like rigid solids until they hit a critical breaking point. From industrial drilling muds to the tube in your bathroom, understanding this threshold is essential for managing complex flows.
A Bingham plastic is a type of viscoplastic material that exhibits a unique dual nature. At low levels of shear stress, it behaves as a rigid, or even elastic, solid. However, once the applied stress exceeds a specific threshold known as the yield stress, the material begins to flow as a viscous fluid. This behavior is often driven by an internal structure—a network of interacting particles like clay or large molecules like polymers—that creates a weak solid framework. When enough force is applied, this structure breaks, allowing the particles to move within the liquid.
This mechanism is why toothpaste remains a coherent plug inside its tube rather than leaking out instantly. It also explains why certain paints can maintain textured surfaces with peaks and ridges; unlike Newtonian fluids, which settle into featureless surfaces, Bingham plastics can hold their shape under gravity once the stress is removed. In engineering, this property is vital for handling slurries and managing mud flow in drilling operations.
Mathematically, describing these flows is more complex than describing standard Newtonian fluids. Unlike Newtonian fluids, which rely only on viscosity to describe flow, Bingham plastics are characterised by both plastic viscosity and yield stress. Because calculating the friction factor for these non-Newtonian fluids is notoriously difficult, researchers use various approximations. While the Buckingham–Reiner equation provides an exact description for laminar pipe flow, its complexity often leads engineers to rely on more practical models, such as the Swamee–Agglarwal equation or empirical expressions like those developed by Darby and Melson.
Opens the Intellect+ feed with this card first. Swipe up for the next one.
Sources
- Summary by Intellect · source: Bingham plastic
To cite this card, link to https://intellectplus.co.uk/app/science-bingham-plastic.
How we source, check and correct cards: Editorial standards.
General information, not professional advice. Spotted an error? Flag the card or see corrections and complaints.
Intellect Plus is a visual educational discovery platform for exploring fascinating facts and ideas. Brain Food, Not Brain Rot. What is Intellect Plus?
Related
More in Materials · More in Science · Latest · A–Z · All topics
