|
 The APL China in San Francisco Bay
|
Imagine a container ship for a moment. It is larger than a small building, larger than several buildings put together, as a matter of fact. If it is a newer ship — called a post-Panamax ship — it is too wide to fit through the
Panama Canal (Question: how wide IS the Panama Canal?). And, when fully
loaded, it carries over 5,000 cargo containers, each loaded with tons of
goods. So, how does it float?
Well, it's a delicate balancing act, but no different ultimately from how any
other ship — from a simple canoe to a racing yacht — floats. Ships float
because of their shape. When in the water, they are able to displace more
than their weight in water. That is, ships are less “dense” than water. The
force of the water a ship displaces creates an upthrust which keeps the boat
afloat.
Thus, it’s not the weight of the ship that matters, but its shape. A steel
block (even one that weighed much less than a ship) would sink instantly,
because it is denser than water. A steel block displaces less water than the
block weighs and thus cannot stay afloat. But a ship, with its outwardly-curved sides pushes aside — or displaces — a great deal of water. Enough to float the ship and its load.
Try it yourself: attempt to float different objects (made of different
materials, sizes, and shapes). What characteristics mark the ones that float?
Container ships face a special challenge because of the weight and size of the
containers they carry. The containers have to be positioned carefully so that
weight is distributed evenly throughout the ship. In addition, containers
must be loaded and unloaded very systematically: if too many containers from
one part of the ship are loaded or unloaded at once, the ship could sink or be
split in half.
Now that you have learned a little about how ships float, can you investigate
how airplanes fly?
|
|
