Getting a Grip on Gravity Aboard a Ship

From The Wall Street Journal:

There’s an endless stream of advice about things that will stop you sleeping well: bright screens before bedtime, too much caffeine, the wrong pillows and so on. Let me add one to the list. It’s almost impossible to get any decent sleep while you’re constantly sliding across the bedsheets down to the end of the bed, and then a few seconds later sliding back the other way.

This sounds extreme, but it’s been a regular feature of my life over the past month. I spent some of November and all of December on a scientific research ship in the middle of the Labrador Sea, as part of an international project to measure stormy seas and how they help the ocean breathe. It was a great opportunity from a scientific point of view, but it came with a built-in challenge—the middle of the ocean during a big storm is a very difficult place to work, because gravity becomes a fickle trickster.

Gravity is incredibly useful, most of all because it’s reliable. We put things on shelves knowing that they’re going to stay there. Faucets point downward because the water will come out and keep going down. But if you need a ship to go in specific directions for scientific reasons, it can’t sit in the most stable orientation amid the wind and the waves. The ship will roll much more than normal and gravity effectively becomes changeable.

You find yourself chasing the water around the shower cubicle because the direction that it’s falling relative to you keeps shifting. Every corridor has handrails that you need to hold onto as you zigzag along. The default assumption is that everything will move, so you have to strap everything down as soon as you move it and if you don’t, it certainly won’t be there when you get back. After one particularly violent night, I got down to my lab to find that a large, heavy instruction manual that I left on a shelf had been thrown onto the top of the printer 3 yards away.

But there is one exception to all this motion. There’s a type of nonslip rubbery mesh table mat that I’ve never seen outside a ship, and anything that’s placed on that will just stay put. The night that the manual took flight, I had left a laptop sitting on a grippy tabletop mat, not strapped down, and I really should have been punished for that mistake by finding the laptop smashed in a corner. But it hadn’t moved.

My savior was friction, and this type of mat is exceptional at creating it. Surfaces are all rough at tiny scales, and so when one object is placed on top of another they only really touch at a small number of tiny points. It’s like one mountain range being placed upside down on top of another one, so that only the biggest peaks actually poke into the other surface, and those points take all the weight.

But the soft rubber is easily squashed, increasing the contact area as the mat molds itself to the underside of the object on top. That makes it much harder for the upper object to slide. When there’s a sideways force, the top of the rubber can also move slightly sideways without breaking, absorbing the force within the mat and reducing the sideways push on the object. That all reduces the sensitivity of the object to the exact direction of gravity. As long as gravity is still mostly downward, the mat will stop things sliding around. This is a game-changer at sea, because “mostly downward” is as reliable as gravity gets.

Link to the rest at The Wall Street Journal (Sorry if you encounter a paywall)

2 thoughts on “Getting a Grip on Gravity Aboard a Ship”

  1. while you’re constantly sliding across the bedsheets down to the end of the bed, and then a few seconds later sliding back the other way.

    Ever wonder why so many sailors use hammocks?

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