You've just cut your finger and you reach for a Band-Aid.

Walking along the Mall, you notice a man and his dog playing with a Frisbee.

It's cold out, and you're glad you remembered to wear earmuffs.

Commonplace objects all, but once upon a time they didn't exist. And they are proof that necessity -- or, in the case of the Frisbee, just having fun -- is the mother of invention:

*Band-Aids were invented by a young husband for his new wife, an inexperienced cook who regularly burned herself cooking.

*Earmuffs were dreamed up in 1873 by a 15-year-old Maine boy, Chester Greenwood, whose ears got cold during New England winters.

*And Frisbees came about when a man recalled the fun he and his college friends had hurling pie plates through the air.

People conjure up all sorts of images when they think of inventors -- a wild-eyed Gyro Gearloose running around a laboratory, an absent-minded professor fiddling with far-out contraptions, or maybe a stern-looking scientist presenting his findings to an equally serious-looking bunch.

Well, if you were to meet 44-year-old Steven Caney, all such presumptions would go out the window. Caney, an inventor, design cunsultant, teacher and author, looks, well, normal, in a pleasant, nondescript sort of way -- trim beard, casual clothes, easy smile. He's clearly comfortable spreading the word:

"Anyone can be an inventor. Everybody has ideas, but very few people do anything with them."

Caney's mission is to get more people -- particularly children -- interested and involved in inventing. Having first won recognition (and $50, from Ford Motor Co.) for an invention (a suspension system for his pushmobile) at the age 13, Caney is convinced that young inventors have an advantage over older, more experienced adults.

"Adults often will get discouraged and say, 'Awww, it'll never work. You can't do that.' Youngsters, on the other hand, will tend to ask, 'Why not?' They often succeed because they are too naive to consider that it can't be done.

"I find that if you can plant the inventing seed early, if you can get kids used to doing things really early, it becomes second nature to them and they don't get held back by obstacles."

It is with that philosophy and goal in mind that Caney wrote Steven Caney's Invention Book (1985, Workman Publishing, 208 pps., $7.95), a work filled with invention trivia, ideas, challenges and success stories.

Fantasy Notebook items -- sprinkled throughout the book -- are especially fun. Featured are useful and fanciful items that "need" to be -- but haven't been -- invented yet: Snap-on pockets, watersoled shoes . . . "These are brainstorms," explains Caney, "that came out of sessions I've had with kids. I go up to the local elementary school and we take an existing invention -- say, waterbeds -- and see what else that could lead to."

Caney leads youthful readers through the mechanics of inventing: setting up, making models and prototypes, naming the product, getting it patented and, of course, marketing it.

Other sections of Invention Book show children how to create their own versions of existing inventions -- string dispensers, back scratchers . . .

There are benefits, he likes to point out, in looking for new possibilities in things that already exist. "I didn't invent crystal radio sets," he explains, "but I reinvented a way to do them."

He offered this "new" product to a manufacturer who balked at Caney's $500 price tag. "They thought that was an outrageous amount to ask for this invention," so he settled for $250 cash and a 5 percent royalty on every set sold. "I've earned over $200,000 on it and it's still on the marketplace, and I still get my check every six months."

Every invention doesn't bring its creator $200,000, Caney is quick to warn. "I've had a few disasters in the marketplace," he admits. "I get rich; I get poor; I get rich; I get poor."

But he does have other sources of income: writing (Toy Book, Play Book, Kids' America, all for Workman Publishing), teaching (he's a professor at Rhode Island School of Design) and design-consulting.

Caney likes to remind potential Thomas Edisons that "80 percent of all the new products that come on the market every year are invented by outside inventors, not companies. Companies depend on independent inventors for new ideas."

Typically, he says, companies will come to him in his consulting business saying, " 'We have a need for an invention.' They'll tell me their capabilities and ask for other products they can produce. What I'll do is create a line of products for them, or at least a line for them to choose from" -- another angle for prospective inventors to pursue.

The danger for an inventor is taking an invention to the marketplace. "If it's a flop, then all of a sudden the inventor is a failure. What do you say then to that next-door neighbor when he asks how your product is doing?"

Kids, however, are mostly immune to this predicament. If their first efforts don't pan out, they can just move on to the next project. "That's the advantage," says Caney, "to being a kid."