Is there a name for this? i remember whn I was a kid-we would take the soft tar that oozed from cracks in the (asphalt paved0 roads, and mold it into little balls. If you threw one of these balls at the sidewalk, it would shatter like glass-despite being soft and pliable in your hands. Whay do substances behave this way? Is glass just a very hard version of a fluid like tar?
They are called viscoelastic materials. Basically, unlike simple elastic materials, like most metals (over a given range of strain,) or viscous materials, like liquids, viscoelastic materials have properties of both. How they react and deform is dependent on how fast the stress is applied. Generally, the faster the stress is applied, the more the viscous part of the material takes over.
Imagine a box filled with thick honey, with a small rod sticking out. Now, if you grab that rod and turn it very fast, the honey is going to resist that turning and you will have to give more torque to turn the rod a given amount of rotation. But, if you turn it slowly, then you can use much less torque for the same amount of rotation.
Oobleck (a mixture of water and cornstarch) is another famous viscoelastic material. If you push your hand into a bowl of it slowly, it’s like a thick liquid and you can submerge it. But if you punch it very fast, your hand will get stopped as the surface hardens. Almost all human hard and soft tissues display viscoelastic properties, too. Believe it or not, human bones are more resistant to deformation the faster the strain is applied. So if you and I both have our arms deformed the same amount, say from me falling off a bicycle and you from lifting too much weight, my bones are less likely to break.
ETA: And glass is another category entirely. Glass is considered a “super-cooled liquid” (or, if you prefer, a an amorphous solid.) Basically, it’s a material that isn’t quite a solid, but not really a liquid either. Basically, you melt down the silica, and then cool it too fast for it to form “proper” crystallization. So instead of being back to the original solid state of the silica, it’s now glass. I think. Someone else will come along and explain glass better than me.
The specific name for the property you describe is dilatant, or shear thickening. It’s the opposite of thixotropic.
If it’s a fluid you’re talking about, it’s called non-Newtonian, in all cases it’s shear hardening.
A rheologist told me about seeing some amazing very high speed photography of water droplets being hit with a projectile at very high speed, and shattering into sharp slivers before these evolved into smaller droplets. It’s hard to imagine, but this fellow is the very soul of sincerity.