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Glass has very diverse uses in the modern world

Examples of glass
You are probably quite familiar with the material known as glass. When you look out a window, you are looking through glass. When you watch something on television or a computer screen, you are looking at a glass screen. We often call something you drink out of “a glass” – even when it is made of plastic!

These are all examples glass made from silica, which you’ll learn is the main ingredient of sand. But, scientists refer to other materials as “glass,” too. Glass feels like a solid, but internally is a little bit like a liquid, because the molecules are arranged irregularly, or not in a pattern, inside. In this article we are focusing on what we normally think of as glass – the material made from silica.

Most of the examples above are probably items you think of as being fragile. If you knock a glass off a counter, it will likely break. So you might be surprised to learn that glass is also used in making things like fiberglass boats and fiber optic cables. Fiberglass boats and fiber optic cables are not fragile at all. These forms of glass have some different properties than the glass used for windows. In addition to everyday items like glasses and windows, glass has made some surprising contributions to the modern world.


Key properties of glass include transparency, non-reactivity, brittleness, and strength in compression

Properties of glass
One of the most obvious physical properties of most glass is that it is transparent. You probably know that if something is transparent you can see through it. Something that is transparent allows light to pass through it. Glass transmits, reflects, and refracts (bends) light, instead of absorbing it. Because light passes through it, we can see what is on the other side of the glass. Being transparent makes glass an ideal material for windows or anything else we need to see through.

Another important property of glass is that it is non-reactive. Something reactive can react with things it comes into contact with – like how iron can rust from exposure to air. Something that is non-reactive does not react with other things it comes into contact with. Because glass is non-reactive, if you put something in glass, like tomato sauce, the glass will not change the taste or composition of the sauce. That makes glass great for uses like storing food or chemicals.

Glass is also brittle. If something is brittle it will not bend before breaking if it experiences a large force, like getting knocked off a counter. That’s why people sometimes prefer to store food in plastic instead of glass.

Glass is strong under compression (pushing forces) and can hold a lot of weight. For example, you can stand on a floor made of thick glass, and it won’t break under your weight. Have you ever been in a glass-bottom boat? They actually exist! However, the glass used in things like drinking glasses and windows is not strong under tension (pulling forces). This type of glass would not be a useful material for making things like the chains on a swing, which get pulled when someone sits down on the seat.


Glass can be modified to change its properties

Regular and safety glass
Like other materials, glass can be modified to change its properties. A material’s properties can be changed by heating, cooling, or working (which means doing something to it, like hammering or stretching) the material. You can also change the properties of a material by adding other ingredients to it.

One example of glass with modified properties is safety glass. If you have ever broken a drinking glass, you know that it breaks into lots of different sized pieces, some of which can be very large and sharp. You can image how dangerous that kind of glass would be in a car accident. Instead, car windows are made from safety glass. Both thermal (heat) and chemical treatments are used to make safety glass. The result is that the outer surfaces of the safety glass are in compression (being pushed in) and its inner surfaces are in tension (being pulled out). The stress is balanced between the molecules, causing the glass to shatter evenly. This makes the glass harder and causes it to shatter into very small pieces. So, if your car’s front windshield is broken in accident, it will shatter evenly into small pieces instead of large dangerous shards. That makes safety glass a much safer material for a car windshield.


Glass fibers are a glass-based material with an additional key property: tensile strength

Fiberglass and glass wool
Glass fibers are long, thin strands of glass. Glass fibers are made by heating and stretching glass into very thin strands, or “fibers”. Unlike regular glass, glass fibers have a lot of tensile strength. A material with high tensile strength can withstand being pulled really hard before breaking.

One use of glass fibers is as a material for insulating buildings. Insulating materials help to slow heat from moving. A home that is insulated will stay cooler in the summer and warmer in the winter. For insulating materials, flexible glass fibers are intertwined into a form sometimes called “glass wool”. If you have ever seen insulating material, it does kind of look like fabric, doesn’t it? The glass fibers trap blocks of air. Gases like air do not conduct heat easily. Glass wool insulation traps air, which makes it an excellent heat insulator.

Another material made with glass fibers is fiberglass. Fiberglass is plastic reinforced with glass fibers. Fiberglass is widely used as a reinforcement material because of its strength. Items reinforced with fiberglass include circuit boards for televisions, radios, and computers. It is also used to reinforce the shells of pools, bathtubs, and boats – not things we typically think of as being made with glass! Although fiberglass contains glass, it has different properties than what we normally think of when we think of glass. Glass fibers used for reinforcement material or insulation do not require transparency, unlike so many other uses of glass.


Optical fibers are glass fibers used to transmit light

Fiber optic cable graphic
Glass fibers that do utilize the transparency property of glass are called optical fibers. Optical fibers are long, thin glass threads that are used to transmit light. Each thread is as thin as human hair. Threads that are grouped into bundles are called fiber optic cables. These cables are used to transmit light, just like a window transmits light. The light that is transmitted represents data that is moving through the wire as a series of light signals. That data might be a conversation you are having on the phone, a text message you are sending, or a video you are streaming online.

Light travels through the center of the fiber optic cable by bouncing off the insides of the cable. Light can travel great distances through fiber optics because the inside of the cable does not absorb any light. Only impurities in the glass cause the light signal to degrade.

Fiber optic cables are replacing the copper wires that were historically used for transmitting data. Fiber optic cables are cheaper, thinner, more flexible, and more lightweight than copper. They also transmit data faster than copper can. Not all communications data is sent over optical fibers. However where optical fibers are used, there is a significant improvement in the capacity and speed of transmitting that data.


The main ingredient of glass is the main ingredient in sand

Sand castle
Glass is used for many things in the modern world from windows to insulation and communication cables. Part of the success of glass has to do with the fact that it is inexpensive to make. It is inexpensive to make because the ingredients for glass are so abundant. The main ingredient in most glass is a compound called silicon dioxide, also known as silica. If you have ever been to the beach or played in a sandbox, you are actually pretty familiar with silica, because it is also the main ingredient in sand. Sand and glass look nothing alike, but sand heated up to very high temperatures forms glass!

To make glass, other ingredients are added to the silica sand. These ingredients are added to change and improve the properties of the glass. For example, something called sodium carbonate lowers the temperature required to make glass. Lead oxide makes glass softer so it is easier to cut, and is also what causes crystal glassware to sparkle. Chemicals can also be added to change the color of glass. The mixture is then heated to high temperatures to melt and become glass.


Glass is found in nature

Obsidian samples
Before people began making glass, they used glass that was made naturally. Because glass is sand heated to very high temperatures, glass can found in nature near very hot sources. One example of naturally occurring glass comes from lightning striking sand. Another source is volcanoes. Obsidian is one type of volcanic glass that was used in ancient times to make arrowheads, knives, and jewelry. Obsidian is still used in jewelry today. Although transparency is one of the key properties of much of the glass we use today, glass does not have to be transparent. For example, obsidian is often black and might look more like a shiny rock than a type of glass.


Glass is a critical material for building and communicating

Glass has very diverse uses. We have relied on glass windows to bring natural light into our homes, schools, and businesses for centuries. More recently, we have also come to rely on glass fibers to move massive amounts of data around the world. Sometimes the use of glass is obvious. When you use a drinking glass or look out a window, you know that you are using glass. Other times, glass is hidden in fiberglass insulation or in the fiber optic cables we use to communicate. Now that you know its many uses, you may never see (or see through) glass the same way again!


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