Long ago Brother Lucas, my high school physics teacher told me that I would weigh less if I were standing on top of the tallest peak in the Andes than I would if I were standing in Death Valley. He explained that every object in the universe exerts a pull on every other object in the universe, and that the force of the pull depends on three things: (1) the mass of the first object, multiplied by (2) the mass of the second object, divided by (3) the square of the distance between their centers. Weight is not to be confused with mass: on earth my weight is the force produced by the pull of the huge mass of the earth on the mass of my puny body. But because the distance between my body on the mountain top and the center of the earth is greater than the distance between my body in Death Valley and the center of the earth, I would weigh less on the mountain, but my mass would be the same. Confusing? It takes a bit of mulling.
In Egypt the unfortunate Captain of the Ever Given freighter got the ship’s nose stuck in the muck in the Suez Canal. As a result, hundreds of ships were idled. Nothing could move in either direction in one of the world’s busiest shipping channels. Gazillions of dollars were lost. All the king’s tugs and all the king’s engineers couldn’t pull the Ever Given straight again. They huffed and they puffed and they pulled and they shoved with no discernible results. Then Brother Lucas’s physics came along and solved the problem.
Remember how he told us that every object exerts a pull on every other object in the universe? The moon is a very massive object, and the sun is a much more massive object. They both are constantly pulling on our massive earth. (That is what keeps the earth in its orbit.) But the sun, as big as it is, is 93,000,000 miles away, while the moon is only a wee fraction of that distance. The pull depends inversely on the square of the distance between objects. So the contest of pulling on the earth is won by the moon, with the sun not giving up, just settling for a lesser effect because of the greater distance. Now consider that three quarters of the earth’s surface is covered by water. As the moon rotates around the earth it is constantly pulling on the oceans, causing what we call tides, the raising and lowering of the surface.
And here is the most interesting part. Approximately twice a month the earth the moon and the sun are in a straight line. They join forces and gang up on the earth. That happens when there is a new moon and again when we have a full moon, two weeks apart. That configuration produces a double whammy effect on the tides: we get very high tides and very low tides at the full moon and again at the new moon. Deep sea fishermen and sailors live by that bit of knowledge and make use of it.
Mother Nature came to the rescue of the Ever Given by raising the tide in the Mediterranean Sea on the north end of the Suez Canal, at the same time raising the level of the tide in the Red Sea on the south end of the Suez Canal. All that rising water came rushing into the Suez Canal. And guess what happened? The Ever Given was lifted from the mucky bottom by all that rising water.
All those experts in Egypt could have saved themselves a lot of trouble and expense if they had known about Brother Lucas and the laws of physics. Perhaps the engineers and sea captains will remember that lesson next time a ship gets stuck in the mud.
How does that law of physics apply to swimming? Not much if you are swimming in a pool. But when you swim in the ocean or when you enter the water in a tidal river (including the lower Columbia) you had best be aware of the tides and the resulting currents. I have yet to meet a swimmer who is stronger than a fast-moving river.