When pressure is applied to a piece of chalk what happens and why?

Answer 1

When you apply pressure to a piece of chalk, it will break. This is because you are pushing, for example, on the sides of the chalk. This action normally results in the object getting thinner in the area where the pressure is greatest, like if you squeeze a piece of chewed gun or putty. But since the chalk is such a hard solid, it has no where to go and breaks in the place with the most pressure. It's just like when you draw with a crayon, if you push down with it on the paper too hard in an effort to gain a darker or stronger color, it breaks in half because you are also squeezing the middle so that your hand stays where it is and doesn't slip down the crayon. The harder you push down, the more pressure you need to apply to the middle so your hand won't slip down, until it breaks.