question: Why is glass able to bend when vibrating, as shown in those incredibly slow-motion videos, but trying to bend under any other condition merely shatters it?
comment: It depends on the thickness of the glass and if it is tempered or not. Temperd glass is a bit tougher to break.But when it does it breaks into small little squares. Instead of big shards of glass that are in the shape of a point. It also depends on the width and the way it is flexed. A small square little piece will not bend while a long rectangular piece will bend a lot more than you would imagine. 1/16 in. Glass will bend a lot more than 1/8 in. Glass. Anything after that thickness is the issue.
passages: It is this compressive stress that gives the tempered glass increased strength. This is because annealed glass, which has almost no internal stress, usually forms microscopic surface cracks, and in the absence of surface compression, any applied tension to the glass causes tension at the surface, which can drive crack propagation. Once a crack starts propagating, tension is further concentrated at the tip of the crack, causing it to propagate at the speed of sound in the material. Consequently, annealed glass is fragile and breaks into irregular and sharp pieces. 
   The strengthening mechanism depends on the fact that the compressive strength of glass is significantly higher than its tensile strength. With both surfaces of the glass already in compression, it takes a certain amount of bending before one of the surfaces can even go into tension. More bending is required to reach the tensile strength. The other surface simply experiences more and more compressive stress. But since the compressive strength is so much larger, no compressive failure is experienced.
   While glass is being moved and installed, it is easy for the glaziers to nick or chip the edges of the glass with various tools. It is also possible for fasteners such as nails or screws used to attach glass stops to nick the glass edges if these fasteners are installed at an improper angle. These small nicks or chips may not result in immediate breakage. However, over time, as the glass expands and contracts, stress concentrations can develop around the nick, leading to breakage. In the case of tempered glass the entire unit usually breaks.
  
  Section::::Binding in the frame.
   Heat-strengthened glass, or tempered glass, is glass that has been heat treated to induce surface compression, but not to the extent of causing it to "dice" on breaking in the manner of tempered glass. On breaking, heat-strengthened glass breaks into sharp pieces that are typically somewhat smaller than those found on breaking annealed glass, and is intermediate in strength between annealed and toughened glasses.
  
  Heat-strengthened glass can take a strong direct hit without shattering, but has a weak edge. By simply tapping the edge of heat-strengthened glass with a solid object, it is possible to shatter the entire sheet. 
   Chemically strengthened glass
  
  Chemically strengthened glass is a type of glass that has increased strength as a result of a post-production chemical process. When broken, it still shatters in long pointed splinters similar to float glass. For this reason, it is not considered a safety glass and must be laminated if a safety glass is required. However, chemically strengthened glass is typically six to eight times the strength of float glass.
   Section::::Chemically strengthened glass.
  
  Chemically strengthened glass is a type of glass that has increased strength. When broken it still shatters in long pointed splinters similar to float (annealed) glass. For this reason, it is not considered a safety glass and must be laminated if a safety glass is required. Chemically strengthened glass is typically six to eight times the strength of annealed glass.
   Section::::Strengthening mechanisms in amorphous materials.:Glass.
  
  Many silicate glasses are strong in compression but weak in tension. By introducing compression stress into the structure, the tensile strength of the material can be increased. This is typically done via two mechanisms: thermal treatment (tempering) or chemical bath (via ion exchange). 
   Glass expands and contracts with changes in temperature and deflects due to wind, so almost all modern glass is set on resilient blocks at the bottom and with space for expansion at the sides and top. The gaskets holding the glass in the frame are also usually resilient to cushion the glass against wind buffeting. If no space is provided at the perimeter of the unit, the glass will bind against the frame, causing internal stresses to develop in the glass which can exceed the strength of glass, resulting in breakage.
  
  Section::::Internal defects and inclusions in the glass.
   Heat strengthened laminated glass is stronger than annealed, but not as strong as tempered. It is often used where security is a concern. It has a larger break pattern than tempered, but because it holds its shape (unlike the "wet blanket" effect of tempered laminated glass) it remains in the opening and can withstand more force for a longer period of time, making it much more difficult to get through.
   where formula_2 is viscosity, "T" is the glass transition temperature, "m" is fragility, and "T" is temperature. Glass-formers with a high fragility are called "fragile"; those with a low fragility are called "strong". For example, silica has a relatively low fragility and is called "strong", whereas some polymers have relatively high fragility and are called "fragile". Fragility has no direct relationship with the colloquial meaning of the word "fragility", which more closely relates to the brittleness of a material.
   Chemical strengthening results in a strengthening similar to toughened glass. However, the process does not use extreme variations of temperature and therefore chemically strengthened glass has little or no bow or warp, optical distortion or strain pattern. This differs from toughened glass, in which slender pieces can be significantly bowed.
  
  Also unlike toughened glass, chemically strengthened glass may be cut after strengthening, but loses its added strength within the region of approximately 20 mm of the cut. Similarly, when the surface of chemically strengthened glass is deeply scratched, this area loses its additional strength.
   Section::::Physical implications.
  
  The physical origin of the non-Arrhenius behavior of fragile glass formers is an area of active investigation in glass physics. Advances over the last decade have linked this phenomenon with the presence of locally heterogeneous dynamics in fragile glass formers; i.e. the presence of distinct (if transient) slow and fast regions within the material. This effect also been connected to the breakdown of the Stokes–Einstein relation between diffusion and viscosity in fragile liquids.
   Using tempered glass can pose a security risk in some situations because of the tendency of the glass to shatter completely upon hard impact rather than leaving shards in the window frame.
  
  The surface of tempered glass does exhibit surface waves caused by contact with flattening rollers, if it has been formed using this process. This waviness is a significant problem in manufacturing of thin film solar cells. The float glass process can be used to provide low-distortion sheets with very flat and parallel surfaces as an alternative for different glazing applications.
  
  Section::::History.
   BULLET::::- Rapid heating (or cooling) may cause uneven thermal expansion putting too much mechanical stress on the surface and cause it to fracture. Fracturing is a concern when people new to laboratory become impatient and heat glassware, especially the larger pieces, too fast. Heating of glassware should be slowed using an insulating material, such as metal foil or wool, or specialized equipment such as heated baths, heating mantles or laboratory grade hot plates to avoid fracturing.
  
  BULLET::::- Hot glass looks like cold glass, so a person must be careful to avoid grabbing hot glassware.
   Thus, thermal motion in liquids can be decomposed into elementary longitudinal vibrations (or acoustic phonons) while transverse vibrations (or shear waves) were originally described only in elastic solids exhibiting the highly ordered crystalline state of matter. In other words, simple liquids cannot support an applied force in the form of a shearing stress, and will yield mechanically via macroscopic plastic deformation (or viscous flow). Furthermore, the fact that a solid deforms locally while retaining its rigidity – while a liquid yields to macroscopic viscous flow in response to the application of an applied shearing force – is accepted by many as the mechanical distinction between the two.
   Any cutting or grinding must be done prior to tempering. Cutting, grinding, and sharp impacts after tempering will cause the glass to fracture.
  
  The strain pattern resulting from tempering can be observed by viewing through an optical polarizer, such as a pair of polarizing sunglasses.
  
  Section::::Uses.
   The inadequacies of this conclusion, however, were pointed out by Frenkel in his revision of the kinetic theory of solids and the theory of elasticity in liquids. This revision follows directly from the continuous characteristic of the structural transition from the liquid state into the solid one when this transition is not accompanied by crystallization—ergo the supercooled viscous liquid. Thus we see the intimate correlation between transverse acoustic phonons (or shear waves) and the onset of rigidity upon vitrification, as described by Bartenev in his mechanical description of the vitrification process.
   Some glassware features barbs (devil's horns, Viking helmet) sticking out the sides of the tapers. Small stainless steel springs are used on these to hold the joint together. The use of springs is of particular benefit when dealing with positive pressures, as they apply enough force for the glass to operate, but will open the taper if an unexpected excursion occurs. This method is considered quite old fashioned, but is still used on some of the most well known and high-end glassware available.
   Section::::Mathematical methods.:Built-in stress (preloaded).
  
  A preloaded structure is one that has, internal forces, stresses and strains imposed within it by various means prior to application of externally applied forces. For example, a structure may have cables that are tightened, causing forces to develop in the structure, before any other loads are applied. Tempered glass is a commonly found example of a preloaded structure that has tensile forces and stresses that act on the plane of the glass and in the central plane of glass that causes compression forces to act on the external surfaces of that glass.
   BULLET::::- comment in Transactions of the Royal Scottish Society of Arts, Volume 4, pp. 255–256 link
  
  BULLET::::- (communication) Edward Sang, "Theory of free vibrations of a linear series of elastic bodies. Part 1.", Proceedings of the Royal Society of Edinburgh, volume 3, 1856–1857, p. 358 link, part 2, pp. 360–362 link
  
  BULLET::::- (communication) Edward Sang, "Proposal of experiments to determine the molecular changes which take place on glass", 1856
   Generally, kiln-glass manufacturers will rate their glasses for compatibility with other glasses they make. In order to be certain that the glasses they use will be compatible, many glass fusers will adopt one manufacturer's glasses to use exclusively.
  
  The stress in two pieces of incompatible glass that were fused can be observed by placing the item between two polarizing filters. This will show areas of tension which will develop stress and fracture over time.
  
  Section::::Techniques.
   The most accurate method of measuring the DBTT of a material is by fracture testing. Typically four point bend testing at a range of temperatures is performed on pre-cracked bars of polished material.
   Acoustic resonance is an important consideration for instrument builders, as most acoustic instruments use resonators, such as the strings and body of a violin, the length of tube in a flute, and the shape of, and tension on, a drum membrane.
  
  Like mechanical resonance, acoustic resonance can result in catastrophic failure of the object at resonance. The classic example of this is breaking a wine glass with sound at the precise resonant frequency of the glass, although this is difficult in practice.
  
  Section::::Types of resonance.:Electrical resonance.
   Because glass transitions and secondary transitions are seen in both frequency studies and temperature studies, there is interest in multidimensional studies, where temperature sweeps are conducted at a variety of frequencies or frequency sweeps are conducted at a variety of temperatures. This sort of study provides a rich characterization of the material, and can lend information about the nature of the molecular motion responsible for the transition.
   Nickel sulfide inclusions ("stones") can be present in the glass. The most common cause of these inclusions is the use of stainless-steel machinery in the glassmaking and handling process. Small shavings of stainless steel containing nickel change structure over time and grow, creating internal stresses in the glass. When these stresses exceed the strength of the glass, breakage results. This type of breakage is almost always found in tempered glass and is indicated by a distinctive "figure eight" pattern, with each "loop" of the figure eight approx. 30mm in diameter.
  
presuppositions: All glass can bend when vibrating.
corrections: Whether glass bends when vibrating depends on its thickness and whether it is tempered or not.
raw_presuppositions: All glass can bend when vibrating. All glass can bend when vibrating.
raw_corrections: Whether glass bends when vibrating depends on its thickness and whether it is tempered or not. Whether glass bends when vibrating depends on its thickness and whether it is tempered or not.