The deep ocean holds many mysteries, and one striking demonstration of its unique environment is the transformation of a common Styrofoam cup. Scientists often attach these objects to deep-sea equipment, only for them to return to the surface dramatically shrunken. This phenomenon offers a tangible glimpse into the immense forces at play in the ocean’s depths, revealing fundamental principles of physics and material science.
The Nature of Styrofoam
Styrofoam, commonly used for disposable cups and packaging, is a foam plastic known formally as expanded polystyrene (EPS). It begins as tiny beads of polystyrene, a plastic derived from petroleum, which are then expanded using a blowing agent. This process creates a material that is remarkably lightweight, composed of approximately 95% to 98% air trapped within a solid plastic matrix. This extensive air content makes it an excellent insulator and gives it its characteristic buoyancy.
While often referred to generically as “Styrofoam,” the term is actually a trademarked name for a specific type of extruded polystyrene foam (XPS) made by DuPont, typically used for construction insulation. The foam used in common cups, expanded polystyrene, is less dense and has irregular gaps between its cells, making it susceptible to external forces.
The Mechanics of Deep Ocean Pressure
The primary environmental factor responsible for the Styrofoam cup’s transformation is hydrostatic pressure. This pressure is the force exerted by the weight of a water column pressing down on a submerged object due to gravity. As one descends into the ocean, the amount of water overhead increases, leading to a dramatic and linear increase in pressure.
At sea level, the air around us exerts approximately one atmosphere (atm) of pressure, which is about 14.7 pounds per square inch (psi). For every 10 meters (approximately 33 feet) of depth in the ocean, the pressure increases by roughly one additional atmosphere. Therefore, at a depth of 1,000 meters (about 3,300 feet), a submerged object experiences approximately 100 atmospheres of pressure, in addition to the one atmosphere from the surface, totaling around 101 atmospheres. This translates to about 1,470 psi, or the equivalent weight of several mid-sized cars on a single square inch. Crucially, this immense pressure acts uniformly on all surfaces of a submerged object.
The Styrofoam Cup’s Metamorphosis
When a Styrofoam cup is lowered into the deep ocean, the immense external hydrostatic pressure acts upon its porous structure. The pressure compresses the tiny air pockets trapped within the polystyrene material. As the air is compressed, the polystyrene material itself is compacted.
The cup retains its original shape because the pressure is exerted equally from all directions, preventing it from crumpling or deforming unevenly. The overall volume of the cup is significantly reduced, becoming much smaller and denser. The material does not return to its original size once the pressure is released because its internal structure is irreversibly altered; the cell walls may collapse, and the material is not perfectly elastic.
Beyond the Cup’s Shrinkage
The shrinking Styrofoam cup serves as a compelling visual aid for oceanographers and marine scientists. It effectively demonstrates the powerful effects of deep-sea pressure, a concept often difficult to grasp due to our everyday experience at atmospheric pressure. Many deep-sea expeditions incorporate this demonstration, with decorated cups becoming unique souvenirs.
Understanding how materials react to such pressures is fundamental for designing equipment used in extreme ocean environments. Submersibles, remotely operated vehicles (ROVs), and other scientific instruments must be constructed with materials capable of withstanding these forces. Unlike Styrofoam, solid objects or those with robust, sealed structures react differently to deep-sea pressure. The cup’s transformation highlights the importance of considering material properties and structural integrity when exploring the deep ocean.