Oobleck is a strange material that is also referred to as a non-Newtonian fluid. This weird substance behaves sometimes as a liquid and a solid the other times. It is made of water and corn-starch entertaining children for many hours. If it is punched it appears to be solid but if picked up it flows away.
Scientists at MIT have studied the magic substance and published a 3D mathematical model that can predict when the oobleck can change from solid to a liquid and vice versa. The findings are published in the PNAS journal.
The scientists explain that the fine particle suspensions demonstrate drastic changes in viscosity on shear which produces interesting behavior. This is captivating to both children and rheologists. In the model, researchers have introduced a 3D continuum model with the help of mixture theory coupling the particle and fluid phases.
The term oobleck is derived from a green substance in the book Bartholomew and the Oobleck authored by Dr. Seuss. This has fascinated researchers for a long period of time as its behavior depends on the way it is interacted with.
The size of the particles plays an important role in this ability of the non-Newtonian fluids. The particles of corn starch are a fraction of the size of a sand grain, so due to their small size, they can be influenced by the temperature and electric charges around them. On moving slowly through the oobleck, the grains repel each other however on hitting it fast, the particles touch giving the feel of a solid. According to Ken Kamrin, mechanical engineer, MIT although this can be created very easily the rules governing it are complex.
This research can be mostly considered as a recreational work, scientists think that this modeling can be used to test oobleck for several materials such as bulletproof vests. Although it is an important question if it can stop a bullet.
Researchers had been working on a model for wet sand but had to change it to obtain the desired oobleck variables. They ran experiments to check if the model was perfect, such as squeezing it between plates and shooting a projectile to a tank having the substance. An X shaped wheel ran through the material at different speeds to help understand the behavior. The model was able to predict the change of oobleck from liquid to solid substance and vice versa as the wheel rolled back.
Journal Reference: PNAS