Why is it that if you put glass that is very hot into cold water it shatters?

Question

thanks

Answer 1

The glass breaks becuase of uneven expansion on all sides.

When you put a hot glass in a cold water, the glass in contact with water contracts, but the coldness takes time to spread uniformly around the glass. Thus while one hot side remains in the same position, other cold side (exposed to water) shrinks, creating differential expansion and the resulting stress, which breaks the glass.

Glass is essentially an amorphous sodium silicate and brittle. The same effect is seen in cast (pig) iron.

Answer 2

Very hot glass will have a high energy content. The molecular structure of the glass will have absorbed enough power to cause some individual molecules to vibrate further from their stable, original position than normal. This re-radiation of energy is what causes the glass to feel "hot"

Upon immersion into cold water, a large percentage of these high energy molecular structures will radiate their excess energy into the water, and attempt to drop back into a stable structure. Unfortunately, this happens too quickly for the underlying surface, i.e. the part of the glass where structures are in a normal energy state. The normal structure is not strong enough to resist the sudden change. As a result, the molecular bonds are sheared and broken at this critial boundary point between high energy and low energy.

Break time.

Answer 3

It is amazing how many of the answers stomp all over the facts and get things half right. Doug's answer is going great until the BTW where he goes all wrong.
Glass is brittle and changes size considerably with temperature. If it is heated it expands like most materials and when part of it is cooled quickly, its brittle (rigid) nature prevents adjustments and strain builds up until cracks form which shatter the glass.
One way to lower the strain is to use glass which expands and contracts less. THAT is what Pyrex is - not tempered. Regular glass expands about 3 times as much as Pyrex (COE is 90-106 compared to 30 for Pyrex if you want to get technical.)

Answer 4

Heat causes expansion, an increase in volume. Cooling is the removal of heat and causes contraction a decrease in volume.

The glass is hot all the way through and is expanded so its volume has increased.

When you drop the glass into cold water. This causes a rapid transfer of heat from the surface area of the glass to the water. This causes an equally rapid contraction at the surface area of the glass. however the glass does not conduct the heat from its central volume as quickly. The result of this is the surface area tries to contract while its volume is remaining almost the same. because the contraction is only occurring at the surface. It can not fit its still expanded volume into its now contracted surface area and it pushes itself apart.

Answer 5

The glass is not tempered. Heat makes it expand and being placed into water abruptly causes shattering because cold makes things shrink, the glass starts to shrink too fast and shatters.

Answer 6

The thermal conduction coefficients are low enough that a large thermal gradient can exist over a short distance. Then, if the thermal coefficient of expansion/contraction is great enough, the force generated over a short distance is enough to cause shearing of the crystaline matrix.

BTW, you -can- get tempered glass (the very first was brand-named 'Pyrex' and it's still synonomous with tempered glass) which doesn' have that problem. Pretty much all labware is made of tempered glass these days.

Doug

Answer 7

expansion and contraction. The glass is expanded due to heat. Placing it in cold water causes it to contract rapidly. The glass, being contracted so quickly, then breaks because it cannot cope with the rapid temperature change.

Answer 8

heat and cold expansion: heat it up and it expands, put it in cold water without cooling, it shrinks to fast and shatters

Answer 9

because of the temperature....when its hot this get bigger and when its cold they shrink so i guess the pressure breaks it