What makes hard materials hard and soft materials soft?

What makes hard materials hard and soft materials soft?

What makes hard materials hard and soft materials soft?

examples of soft materials - Something is hard if, when the atoms are pushed, they don’t get out of the way.

An example of a hard material would be diamond.

When you push the surface atoms in a diamond crystal, the atoms try to move. But the electrical energy increases very quickly as the atoms are displaced and so it takes lots of energy to move the atoms even a tiny distance. So pushing hard doesn’t change the shape.

An example of a soft material would be rubber.

In rubber, atoms are arranged in long strings that are tangled together. However, the strings can slide past each other so when you press the surface of rubber, the electrical interactions cause the atoms to change shape.

Hardness and stiffness are often confused because many things that are hard tend to be stiff. But not rubber.
Stiffness is a measure of how much force is needed to squash or stretch something. Diamond is very stiff. Rubber is not stiff. Both will return to their original shape if they have not been deformed too much.
Hardness is a little more complicated. Different materials require a different amount of force to make the individual atoms slide past each other. Diamond atoms do not slide past each other as easily as Aluminum atoms do. If you press a diamond into aluminum, the area of damage remaining is divided by the force to calculate the hardness.
There are many ways of making things harder for instance aluminum can be made harder by alloying with other atoms such as silicon, copper or magnesium to make it harder for atoms to slide past each other.
In rubber the strings of atoms slide past each other when pressed. But because the strings are linked at various points along their length, when the force is removed the strings return to their starting place. Because rubber returns to its original shape rubber is infinitely hard.
Rubber’s stiffness is also a bit weird, as you stretch an elastic band closer to its breaking point it gets stiffer.

With the information we provide about  examples of soft materials
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