Welcome to March. This is an important month: Spring begins! In our region, the weather may stay pretty cool right up into April. Even so, the days are getting longer, and the sun is getting warmer every day. Nature is beginning to give signals that a change in seasons is on its way. Buds swell on trees. Bulbs push their green tips out of the ground.

There's one more sure sign of spring: People start playing Frisbee. If you visit downtown Washington and pass by the Mall, you might see several of the bright plastic discs flying through the air.

Maybe kids have started playing Frisbee out on your playground at school. Spring and Frisbee-playing just seem to go together.

You may find it hard to believe, but when Frisbees were first invented they were kind of a flop. An inventor named Fred Morrison made the first Frisbees after World War II ended. But he called his invention "Morrison's Flyin' Saucer." The earliest saucers were made of metal. They were too heavy to fly well. Making the saucer-shaped toys out of plastic worked much better.

A California company called Wham-O bought Morrison's invention in 1955. Wham-O employees called the toy a Pluto Platter, but again, it just didn't catch on. Then the people at Wham-O heard about an East Coast college fad. Kids on campuses loved playing a game with pie tins from a factory in Bridgeport, Conn. The Frisbie Pie Co. made the pie tins and stamped their name on each one. To keep up with the fad, Wham-O changed the spelling and named its flying saucer toy the Frisbee.

In the 1960s, playing Frisbee caught on. And people have been playing it ever since. Frisbee experts -- and there are lots of them -- estimate that some 80 million kids and adults have sent Frisbees whizzing and floating through the air.

An experienced Frisbee player can throw the disc more than 200 feet! A champion can send the saucer zooming over 400 feet -- although that's a rare feat. People play Frisbee golf and Frisbee soccer. There are international tournaments. There's also a challenging, football-like game called Ultimate Frisbee.

Michael Conger, the men's overall Frisbee champion in Maryland, reports that the current world records for Frisbee distance-throwing are: about 490 feet in the junior division (kids 19 and under); about 613 feet in the men's division; and about 409 feet in the women's division. A Swede holds the junior title, an Australian the men's title. The woman's title belongs to an American.

Conger -- whose Frisbee nickname is Cap'n Snap -- advises young Frisbee tossers to get in touch with their local parks and recreation department to find out about competitions they can join. The 1988 Maryland state championship will take place in Baltimore in October, so it's time to start practicing your technique.

So how do these spinning platters work? The secret is in the pushing power of air. Like an airplane, a Frisbee flies because of two forces: lift and thrust. Lift comes from air pressure underneath the Frisbee.

Because the top of the Frisbee is curved, the air on top travels a greater distance as the Frisbee goes by. So the top air must go faster. And faster air doesn't have time to push down on the Frisbee as hard as the slower air underneath is pushing up.

Airplane wings have a similar shape. It's called an airfoil.

The science of studying air's marvelous ability to lift things that move through it is called aerodynamics. "Aero" means air; "dynamics" means movement.

When an airplane flies, its thrust, or forward movement, comes from its engine. Your skillful toss provides the thrust for a Frisbee flight. Moving forward keeps a stream of air flowing around the Frisbee, providing that lift you just learned about.

You can't throw a round rock and expect it to float gracefully through the air. The thrust is there, but the lift isn't.

A Frisbee floats back to earth after a while because gravity pulls it back down. A force called drag caused by friction in the air also slows the flight down.

The spinning of the Frisbee -- if you throw it right -- is what keeps it from wobbling.

A player makes the Frisbee go straight, skip, hover in the air or fly straight by controlling the angle of release. The angle of the Frisbee in space determines the rate at which air flows over and under its curved surfaces. Frisbee players like to say, "Flat flip flies straight." That means giving the disc a sharp, backhand flip with your wrist. There are lots of other ways to throw the Frisbee. Experiment until you find the throws that work best for you.

Try This!

Frisbee became popular after college students invented games to play with the flying discs. Players have already come up with Frisbee golf, football and soccer. Can you invent a game using a Frisbee? If you do, send a description and rules to Catherine O'Neill, Health Section, The Washington Post, 1150 15th St. NW, Washington, D.C. 20071. Make sure your game is safe and fair. Great ideas will be published in a later column.

Catherine O'Neill is a children's writer in Silver Spring.