« October 28, 2017 | Main | October 30, 2017 »

October 29, 2017

Egyptian Cat-Shaped Coffins


Circa 664 B.C.E., they were used to bury venerated felines.

From "Soulful Creatures: Animal Mummies in Ancient Egypt," at the Brooklyn Museum through January 21, 2018.

October 29, 2017 at 12:01 PM | Permalink | Comments (0)

Experts' Experts: Why do pens have rubbery grips?


I've wanted to know the answer to this question since forever; it's kept me up at night.

The significance of this research, published in the August 22, 2017 issue of the Proceedings of the National Academy of Sciences:


Why does gripping a pen, tool, or handle feel more secure when it is coated with a rubbery material? The keratin of the skin outer layer is stiff and rough at a small scale. When encountering a smooth, stiff, and impermeable surface, such as polished metal or glass, the actual contact area is initially small as is the friction. Because the keratin softens when it is hydrated by the moisture secreted from the sweat pores, it requires many seconds for the contact area to increase to the value reached almost instantaneously with a soft material, such as a rubber. This mechanism might be used by our tactile sense to identify materials and has implications for the design of tactile displays.



Below, the abstract of the paper that finally put paid to my ignorance.


The process by which human fingers gives rise to stable contacts with smooth, hard objects is surprisingly slow. Using high-resolution imaging, we found that, when pressed against glass, the actual contact made by finger pad ridges evolved over time following a first-order kinetics relationship. This evolution was the result of a two-stage coalescence process of microscopic junctions made between the keratin of the stratum corneum of the skin and the glass surface. This process was driven by the secretion of moisture from the sweat glands, since increased hydration in stratum corneum causes it to become softer. Saturation was typically reached within 20 s of loading the contact, regardless of the initial moisture state of the finger and of the normal force applied. Hence, the gross contact area, frequently used as a benchmark quantity in grip and perceptual studies, is a poor reflection of the actual contact mechanics that take place between human fingers and smooth, impermeable surfaces. In contrast, the formation of a steady-state contact area is almost instantaneous if the counter surface is soft relative to keratin in a dry state. It is for this reason that elastomers are commonly used to coat grip surfaces.

October 29, 2017 at 10:01 AM | Permalink | Comments (0)

Rocket Moon Clock — "Watch time fly"


• Steel and thermoplastic elastomer

• Requires 2 AA batteries (not included)



October 29, 2017 at 08:01 AM | Permalink | Comments (0)

« October 28, 2017 | Main | October 30, 2017 »