Slime has captivated people for generations with its unique texture and playful properties. This substance can stretch, ooze, and break, making its classification a common point of curiosity. The question often arises: is slime a solid or a liquid?
Defining States of Matter
Matter exists in three states: solid, liquid, and gas. A solid possesses a definite shape and a fixed volume, with its particles tightly packed and vibrating in place. An ice cube maintains its form unless an external force changes it.
Conversely, a liquid has a definite volume but lacks a fixed shape, conforming to its container. Its particles are more loosely packed, allowing them to move and slide. A gas, by contrast, has neither a definite shape nor a fixed volume, expanding to fill any container.
How Slime Behaves
Slime exhibits characteristics that challenge traditional classifications. It can be stretched slowly like a liquid, yet it will snap if pulled quickly, similar to a solid. When left undisturbed, slime will gradually spread out and take the shape of its container, much like a liquid. However, if a sudden force is applied, such as punching it, slime can feel firm and resist the impact.
Slime’s behavior stems from its polymer chains. Slime is made by cross-linking polymer molecules with a borate ion solution. These cross-links act like temporary bonds. When a gentle, slow force is applied, these bonds can gradually break and reform, allowing the slime to flow. Under rapid stress, the bonds do not have enough time to rearrange, causing the material to resist the force and behave more rigidly.
Slime’s Unique Classification
Given its dual nature, slime is not a traditional solid or liquid. Instead, it is classified as a non-Newtonian fluid. A non-Newtonian fluid’s viscosity, or resistance to flow, changes depending on the stress or force applied. This differs from Newtonian fluids, like water, whose viscosity remains constant.
For slime, more force or stress applied increases its apparent viscosity. This property is known as shear thickening. When gently poured, low shear stress allows polymer chains to slide, flowing like a liquid. However, under high shear stress, such as rolling or hitting it, the polymer chains entangle and resist movement, causing the slime to temporarily act like a solid.
Common Non-Newtonian Fluids
Slime is not the only substance that behaves as a non-Newtonian fluid. Many familiar items exhibit similar properties. Ketchup is a shear-thinning non-Newtonian fluid, meaning its viscosity decreases with increased shear stress. This is why shaking a bottle of ketchup makes it easier to pour.
Another example is a mixture of cornstarch and water, called oobleck. This mixture is a classic shear-thickening fluid, much like slime. If you slowly dip your hand into oobleck, it feels like a liquid. However, if you punch it, it becomes firm and resists the impact.