In preparation for the Eagles NFC Championship game, Philadelphia police greased up light poles and mailboxes around the city in hopes of preventing jubilant fans from climbing on them — a celebration that could lead to injuries and property damage. Their lubricant of choice was Crisco, a thick shortening used for baking, that is also pretty slippery. But Drexel Engineering Professor Hisham Abdel-Aal, PhD, who is an expert in tribology (the study of friction) recently suggested in a Philadelphia Inquirer story that other lubricants might be better suited for this particular application.
“In theory Crisco should work, but other lubricants like motor oil, machine grease, and even lard would work better,” Abdel-Aal told The Inquirer.
To approach the challenge of making poles so slippery that they can’t be climbed, or, in tribology terms, making it not worth the mechanical effort invested to overcome the lubricant effect, Abdel-Aal breaks it into three parameters:
- The lubrication is meant to separate two rough surfaces – in this case, the clothes of the climber, his hands and feet, and the pole. So it must be thick enough to coat both of them without rubbing off, even after multiple attempts to climb the pole.
- It also needs to be thin enough to actually be slippery, but not so thin that it won’t be overcome by the griping force exerted by a climber.
- It must also be durable enough to maintain its form in cold weather, without becoming so thick that it’s no longer slick.
So, the trouble with Crisco? It’s too cold in Philadelphia right now.
“In theory, any lubricant will work, however when you factor in how many attempts would take place on the same object, and the cold environment, other options may be more feasible. For a cold metal pole in Philadelphia after an Eagles victory, one needs a chemically stable, almost temperature proof, tamper-proof, lubricant. The problem with Crisco is that it’s unstable in severe cold weather — it will act like butter in a freezer, becoming really solid with almost no gripping resistance.”
Abdel-Aal also suggests that the determination of Eagles fans would pose a problem for the cooking grease.
“Repeated attempts on the same general area of the pole will cause local melting of Crisco layers. Crisco, by default, is designed to melt at relatively moderate temperatures. When exposed to freezing temperatures it might act like a peeling layer of paint that could locally peel and drop off.”
His suggestion? Use the real stuff if you want to grease a pole.
“Industrial grade lubricants, on the other hand, are designed for higher chemical stability. They resist fluctuations in temperatures and multiple loads, this makes them better for application on the poles, given that the appropriate thickness of the lubricant is applied.”
Or, go the other route…
“The problem also may be solved based on the other extreme — prevention of free motion. One could achieve this by applying a sticky substance to the pole, such as industrial grade adhesive. In this manner the effort invested in initiation of motion might be prohibitive.”
For what it’s worth, Philly’s #CriscoCops said they’ve cooked up a different plan to keep fans on the group after the Super Bowl.
“I can’t tell you that there won’t still be attempts, but I just would suspect that some of them would be far more difficult than they were with the Crisco attempts,” Police Commissioner Richard Ross told The Inquirer.
While this question is one of the more unusual ones that might come up in tribology, its practitioners have played important roles in the development of several things we encounter on a more regular basis including makeup, chalk, fountain pens, touchscreens and automobile brake pads. At its more advanced levels, tribology research is currently helping to improve vehicle efficiency, self-healing surfaces and the technology used on space shuttles and stations.
Abdel-Aal and his collaborators in France and South America are developing ways to create engineered surfaces inspired by nature. Research that could one day be applied to make joint replacements more durable through controlling their levels of friction and rate of wear.
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