Glass

June 10, 2022

I made a quick run to the market yesterday and when I got back to the car, I noticed a grasshopper hanging onto the outside of the passenger side window.  This is hardly a rarity and I paid it no mind as I sped off for home.  When I got up to speed, I glanced over and even though the wind was blowing the hopper to one side, it was still clinging tenaciously to the glass.  The hopper held on for half a mile (0.8 km) as I drove through town.  It was not until I stopped to turn that the hopper finally jumped off the glass.  While I could not blow him off in the wind, I guess he decided the free ride was over.

When I looked online, I found glass is a non-crystalline, often transparent amorphous solid, that has widespread practical, technological, and decorative uses.  Glass is most often formed by rapid cooling (quenching) of the molten form.  While most glass is manufactured, volcanic glass occurs naturally.  The most familiar type of manufactured glass is “silicate glass”, which is based on the chemical compound silica (silicon dioxide, or quartz), which is the primary element of sand. Archaeological evidence suggests glass-making dates to at least 3,600 BCE in Mesopotamia, Egypt, or Syria.  The earliest known glass objects were beads.  Due to its ease of formability into any shape, glass has been traditionally used for bowls, vases, bottles, jars and drinking vessels.  Glass can be colored by adding metal salts or painted and printed as enameled glass.  The refractive, reflective and transmission properties make glass suitable for manufacturing optical lenses, prisms, and optoelectronics materials.  Extruded glass fibers have are employed as optical fibers in communications networks, thermal insulating material when matted as glass wool, or in glass-fiber reinforced plastic (fiberglass).  I have learned the hard way that glass wool cuts.

Numerous insects and certain amphibians and reptiles (tree frogs and geckos) can walk on and cling to smooth surfaces, including glass doors and windows.  In most insects, this is done by the large number of tiny bristles or hairs on the bottom of their feet.  Electron microscopes have shown “smooth” glass surfaces have microscopic bumps and fissures which serve as footholds for the tiny hairs.  The foot segments, or tarsi, at the end of insect legs also possess claw-like structures that help the insect hold on to different types of surfaces.  The tarsal claws grip the tiny irregularities of the surfaces.  Grasshoppers also make use of adhesion.  On a smooth glass, the insect hold on using the adhesive action of hairs located on sticky pads (known as the arolia or pulvilli) on the tarsi.  Grasshoppers have pads on each of their tarsal segments that contain numerous hairs that secrete an oily substance that causes the tips of the hairs to adhere to the surface.  The substance provides the traction and stickiness that allows hopper to hold on to the glass.  The combination of hairs, claws, sticky pads, and microscopic footholds let the hopper ride.

THOUGHTS:  While most see a window as a solid pane of glass, physicists looking at the glass on a molecular level have questioned whether glass is a solid or merely an extremely slow-moving liquid.  In physics, glass is a solid, but glass lacks the first order phase transition, meaning it does not have a volume (size), entropy (randomness), and enthalpy (heat content) throughout its transition range from sand to glass.  This sets glass apart from typical solids, and in this respect, glass resembles a liquid.  The atomic structure of glass is like that of a supercooled liquid and glass behaves like a solid when it is cooled below its glass transition temperature.  That means only the right questions can address (let alone find) the right answer.  When we deal with people, we often find the same is true.  We need to take time to learn the questions before we can expect to hear the answers.  Act for all.  Change is coming and it starts with you.