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The strange behaviour of the oobleck can now be predicted by researchers

The strange behavior of the Oobleck can now be predicted by researchers

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


Blueberry pancake

Researchers explain the unique movement of Pancake when swirled

When a glass filled with wine is swirled clockwise, the wine will also spin in the clockwise direction, however, while making a blueberry pancake, if it is swirled in the clockwise direction, the pancake spins in an anticlockwise direction.

The same is the case with a glass of beads. A few beads will rotate clockwise when the glass is swirled clockwise. However, a lot of beads in a glass when swirled clockwise will rotate counterclockwise.

Lisa Lee, a graduate student of Applied Physics at School of Engineering and Applied Sciences, Harvard said she was surprised at the behaviour of these exact same objects under the same situations.

The research team set about to understand the physics behind these actions and it turns out that friction is responsible for this. Beads are a part of a class of material called granular media, which means a collection of macroscopic particles such as sand or snow. The work appears in the Physical Review E journal.

Wine rotates clockwise when moved clockwise due to wine being a liquid-like granular media in low friction, while pancakes rotate in an anticlockwise direction when rotated clockwise which is similar to granular media under high friction.

Macroscopic particles are very interesting as they can move like a liquid or a solid depending on the conditions. Sand flows like a liquid in an hourglass but acts like a solid to support your weight on beaches. The object transition from liquid to solid has been an open question for decades.

Lee and the researchers found out that smaller groups of beads will have lower effective friction than larger pairs of beads which results in the transition from liquid to solid. When one particle rolls in one direction it experiences little friction however if many particles which are in contact with each other roll in the same direction, then they experience a large amount of friction which causes the group to solidify and thus change the behavior.

Using computer simulations, Lee and co-authors, John Paul Ryan and Miranda Holmes-Cerfon showed that in the absence of friction, the particles never solidified, no matter the quantity in which they were present. The rougher the particles were, the quicker was the transition from liquid to solid.

Shmuel Rubinstein, Associate Professor of Applied Physics at SEAS and senior author of the study said that this is an interesting case of system-size behaviors emerging from local interactions. The emergence of coherent circulations is an exciting subject for study like the case of 2D turbulence and active spinners. It is quite interesting that daily objects such as marbles and dishes can demonstrate similar physics.

Journal Reference: Physical Review E.