Brittle materials


When a hammer hits a brick it shatters. The pieces of shattered brick have sharp edges. Glass, chocolate and other brittle materials shatter in a similar way to brick.

Why doesn't brick shatter in a wall?
You may think that the bricks at the bottom of a wall would crush under the weight of the bricks above them. This doesn't happen because the weight of the wall is not enough to break the brick apart. Brittle doesn't mean weak. Most brittle materials are very strong, especially when squashed and when the weight is increased slowly, such as happens when a wall is built.
If, however, you want to knock down a wall, you can easily do so just by striking it with a large weight because the sudden shock will shatter the brick.

Are shells made by animals brittle?
Yes they are. Nevertheless, they are strong enough to keep out most attackers. Only a very few animals have found ways to break shells, and then, only some kinds of shell. For example, snails are not safe from the song thrush because it has learned to hit them on a stone. The sea otter uses a stone in a similar way. When it catches a crab or mussel or other shellfish it lies on its back in the water, puts a stone on its chest and hits the shellfish against the stone with its paws. The Egyptian vulture breaks open ostrich eggs by picking up a stone in its beak and hurling it at the shell.
Are bones brittle?
Yes. There is no difference between a leg bone, for example, and a tube of any other brittle material. If it is struck a sharp blow it will shatter inside the leg and the sharp edges of the shattered bones can cut muscles and skin. However, bones are surrounded by padding made up of muscles and skin, so they do not break very often.


Can we make a playground safer?
Yes we can. We can use cushioning materials on the ground. Sand and wood chips are cushioning materials and help to stop a fall resulting in a broken bone. However, you can't cover a playground entirely in cushioning materials or you will not be able to play ball games, so there is a sensible limit as to what can be done.

Can the place where a material shatters be controlled?
Yes it can, and this property is used to cut tiles and glass. If a piece of tile has to be cut, a line can be scratched into the surface. This weakens the tile along the scratch line. As a result, the tile may be snapped along the line. Glass is scratched with a diamond-tipped blade and then snapped in just the same way as the tile.
A block of slate has natural lines of weakness in it. As a result, it can be broken into thin sheets by driving a chisel into it with a hammer. The sheets are used for roofing materials.
Flint is a rock that was used by Stone Age people. When it is struck, small pieces are chipped off. By carefully striking a flint, a process called flint napping, the places where the breakage occurs can be controlled so that the flint can be shaped into an axe, arrow head or knife.
How are brittle materials transported?
They are packed in cases and surrounded by cushioning materials so that they do not receive sudden knocks. The packing materials may be paper, cloth, straw, plastic balls, plastic foam or a many other kinds of flexible or elastic material.