Random Science

11/9/2019

Chemistry: Towering Structures and Tentacles!

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When people think of chemical reactions used for show, they normally think of those that produce explosions or fire, or solutions and gases of pretty colors. However, the chemical reactions shown in the videos below produce structures that emerge from the reaction like tentacles of a being from another dimension or alien edifices.

NileRed made a YouTube video that went viral in 2017, and which I have mentioned before in my blog. This is a video of the amalgamation reaction between mercury and aluminum. The reaction takes place slowly, so it was sped up for the video. If you want to skip ahead to the emergence of the first structure, it takes place around minute two.

In the next video, also by NileRed, the reaction is more impressive as it takes place in real time. This is the so called Pharaoh’s Serpent, which used to be sold as a firework in Germany until it was banned due to the highly toxic compounds that it generates. Below is the short version of the video. If you want the long version with all the explanations of the complex chemistry that is going on, you can find it here.

The last video is by the folks of Home Science where baking soda heated with sugar produces an entity called “The Black Fire Snake”. Unlike the two videos above, this one has the advantage that this is something that you can try at home because it doesn’t involve or generate toxic compounds (as always be mindful of safety when using fire).

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11/3/2019

The Weissenberg Effect and Other Amazing Things About Non-Newtonian Fluids

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When a spinning rod is inserted into a normal fluid like water, the spinning of the rod will introduce a rotation into the liquid that will push it outwards. When you step on water, you will sink. When you subject water to sound waves, it will cause ripples in the water surface and maybe even make it splash, but the water will remain liquid. This is because water and other such liquids are what are called Newtonian fluids. These are fluids whose viscosity always remains constant. But there are other types of liquids that are called non-Newtonian fluids which have some rather amazing properties due to the fact that they can change their viscosity in response to stresses or forces applied to them.

One property of non-Newtonian fluids is shown in the video below. When a spinning rod is inserted into the fluid, the shear stress of the spinning rod will cause the fluid to thicken and be drawn to the rod creating an inward force that will push the fluid in contact with the rod upwards. This is called the Weissenberg effect after the Austrian physicist Karl Weissenberg who studied it.

When you suddenly apply pressure to a non-Newtonian fluid such as cornstarch, the stress induced on the liquid will turn it momentarily into a solid. This property allows you to walk on the liquid or even ride a bike on it as shown in the video below.

Sound waves can also introduce shear stress into cornstarch leading to some interesting effects as shown in the video below.

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Chemistry: Towering Structures and Tentacles!

The Weissenberg Effect and Other Amazing Things About Non-Newtonian Fluids

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