Challenging Conventional Wisdom

For years, John Stossel and "20/20" have been challenging common wisdom, finding the real story behind the things you believe to be true and adding to a very long list of "Myths, Lies and Downright Stupidity."

But there are still more myths out there and Friday's "20/20" will help you determine fact from fiction.

To zap or not to zap? This year marks the 40th anniversary of the mass market microwave and these days the majority of Americans rely on one in their kitchen. But many people still wonder what materials are safe to put in the microwave, particularly plastic.

New York mother Jeannie Wang is worried about the plastic containers she uses regularly. "I'm concerned that chemicals in the plastics might leach into the food and that might be harmful for the baby," she said. But are microwaves really dangerous?

It's beach season and what woman wouldn't kill for firm, flat abs, or a guy for a perfect six-pack?

David Zinczenko, the best-selling author of "The Abs Diet," says, "In survey after survey, men and women are saying that abs are the ultimate symbol of sex appeal … not biceps … not pecs … not butt. It's abs.

Are six-packs perfected in the kitchen or the gym? Are sit-ups really the secret to six-pack abs or is the idea that abdominal crunches flatten the stomach a fitness myth?

People say a falling cat always lands on its feet. Is that why they're said to have nine lives? We asked Ann Hohenhaus, a vet at New York's Animal Medical Center, which studied cats injured in falls from buildings. It's called High-Rise Syndrome.

"The hospital got baskets full of hate letters from people who assumed that we threw cats out of windows. … We didn't throw them out. They fell on their own," said Hohenhaus, who'll reveal whether or not cats really always land on their feet.

Spoiled, selfish, bratty and bossy are terms often used to describe only children, which suggests that being an only child is undesirable. Is there a grain of truth to the stereotype?

The myth of the only child dates back to the late 1800s when G. Stanley Hall, known as the founder of child psychology, called being an only child "a disease in itself."

Susan Newman, a Rutgers social psychologist and author of "Parenting an Only Child," says this myth has been perpetuated ever since. "People articulate that only children are spoiled, they're aggressive, they're bossy, they're lonely, they're maladjusted." What do so-called "onlies" think about the myth? Their answers may surprise you.

Fabulous Fido … Spunky Sparky … Marvelous Moxie. There are more than 74 million dogs in the United States and their owners know they're more than best friends. But can dogs help hunt down diseases? Can they smell cancer? For years anecdotal stories have indicated just that. But what does science say? We'll share the answer to this doggie dilemma.

Whether it's driving while talking on your cell phone, sending emails during a business meeting, or listening to music while you're working, it seems multi-tasking has become a way of life. Employers, parents, and even kids are trying to get more done in less time. But,does multi-tasking really help you become more efficient? And what happens to your brain when you're trying to complete two important tasks at once? Does multi-tasking help, or hurt?

Find out all the answers Friday on "20/20" at 10 p.m. EDT.