How Do You Push a Big Ship Like the Queen Elizabeth II With Your Hands and Overcome Static Friction?

It’s possible to move a large ship like Navy destroyer with your bare hands, by leaning against a stanchion on one ship, with both hands across the narrow gap to a similar stanchion on the ship, and pulling hard.

For a while there may seem to be no result, but slowly the gap between them will begin to diminish until the two ships come together quietly, and without fuss or noise, into contact.

And, left alone, they will remain in contact. Then, by reversing the process over a similar timescale, and substituting a push for a pull, the two ships are able to return to their starting positions. The process was remarkably simple.

The QE2 is just a trifle larger than a Navy destroyer but I believe that the only difference would be in the timescale required to move the ship. Should there be an opportunity to try this experiment with such a large vessel we would advise that you take care not to hold your breath while pulling.

There is no threshold force that needs to be overcome to move a ship in the absence of wind or current. In fact it is remarkably easy for an unassisted person to move a large ship. This can be explained in terms of kinetic energy (E) and momentum.

Consider a ship with a mass of 20,000 tons. If the ship is given a velocity of 0.5 inch per second then its energy, E = 1/2 mv2 is about 1,000 joules. A thousand joules is a very modest amount of energy. It is the energy expended by a 120-pound man climbing up a 6-foot-high flight of stairs.

At 0.5 inch per second the ship’s momentum, mass x velocity = 2 x 105 newton-seconds.

The 120-pound man can impart this to the ship by applying his full weight for 400 seconds. If he moves the ship by standing with full weight on one of the mooring lines, he will have descended by 6 feet by the time the ship is moving at 0.5 inches per second.

Actually when a ship is set in motion, a comparable mass of water is also set in motion at a comparable speed.

Consequently the kinetic energy and momentum calculated above have been underestimated by a factor of two or so. However, the main conclusion stands: an unaided person can easily move a ship.

The ship will move. Fluid forces don’t have a limiting static friction. We can think of these frictional fluid forces as being directly proportional to the speed of the ship. They are close to zero when the speed is close to zero, and so on.

So push, and good luck.

About Karen Hill

Karen Hill is a freelance writer, editor, and columnist. Born in New York, her work has appeared in the Examiner, Yahoo News, Buzzfeed, among others.

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