phere at the surface of our planet measures about 14.7 pounds (6.67 kilograms) per
square inch, or a 1 inch (2.54 centimeters) square column of air weighs 14.7
pounds. This changes depending on the altitude. For example, at an altitude of
10,000 feet (3,048 meters), the air pressure decreases to 10.2 pounds (4.63 kilo-
grams) per square inch.
But a car, truck, SUV, or bike tire needs more pressure in order to inflate. By
increasing the number of atoms inside the tire, there are more collisions between the
atoms and more pressure exerted on the sides of the tire. In other words, a pump
stuffs more air into a constant volume (the confines of the tire), so the air pressure
within the tire rises. A car tire’s pressure is typically at about 30 pounds (13.61 kilo-
grams) per square inch; a bicycle tire’s pressure can be around 90 pounds (40.82 kilo-
grams) per square inch.
What is the purpose of the numbers found in a mailing address?
The Zone Improvement Plan (or ZIP) Code is a grouping of numbers assigned by the
U.S. Postal Service to designate a local area or entity in order to speedily deliver and
distribute mail. ZIP Codes most often refer to a street section, a collection of streets, a
structure or building, or a group of post office boxes, but the numbers do not rigidly
conform to boundaries of cities, counties, states, and other places.
Depending on the area, a ZIP Code includes 5, 7, 9, or 11 digits. In the most common
codes—five-digit ZIP Codes—the first digits divide the country into ten large groups of
states numbered from 0 in the Northeast to 9 in the far West. Each state is divided into
geographic areas identified by the second and third digits of the ZIP Code. For example,
New York and Pennsylvania have ZIP Codes starting with numbers between 090 and 199;
Indiana, Kentucky, Michigan, and Ohio begin with numbers between 400 and 499. The
fourth and fifth digits of a ZIP Code identify the local delivery area.
MATH AND THE OUTDOORS
How is the amount of rainfallmeasured?
The amount of rainfall—liquid precipitation that falls to the surface—is measured by
a rain gauge. The most commonly used free-standing rain gauge is a cylinder with
increments (most often in inches) inscribed on the outside of the tube. It is put in an
area that is not obstructed by buildings, trees, or other tall structures than can impede
the collection of rainfall.
The rain gauge can also measure snow, but added steps are needed to calculate
this. In this case, a rain gauge measures the liquid equivalent of snow. This is why
meteorologists will often say that a snowstorm that produces 10 inches (25.4 centime-
ters) of snow will have a liquid equivalent of 1 inch (2.54 centimeters) of rain, or a 403