For the past half-century, PBS programs have provided rudimentary, but crucial, lessons about grammar and storytelling for their pint-sized viewers. If Sesame Street taught kids the alphabet, Reading Rainbow got them thinking in complete sentences.

Eventually, kids graduated to middle school and started to expand their curiosity. From 1983 to 1998, another PBS program titled Newton’s Apple was able to satisfy it.

The half-hour series anticipated a lot of question-and-answer formats that are still popular today, including Mental Floss’s own Big Questions installments. Each week, host Ira Flatow would select a query sent in by a viewer or provided by a member of the studio audience: What is fiber optics? How much of the body is fat? What makes our ears pop? Why do peeled onions make us cry? In live-to-tape or pre-recorded segments, Flatow would delve into the topic, offering demonstrations and expert opinions that illustrated the show’s explanations.

Flatow, a former science reporter for NPR, drew comparisons to comedian Groucho Marx and often displayed a participatory bent, swimming with dolphins or gliding up in a hot air balloon. Celebrities would also make the rounds: Betty White once helped explain why cats purr. If there was a question or concept that ever puzzled a kid, Newton’s Apple had probably offered up an explanation.

“Despite the fact that we try to make science interesting and amusing, I do not intend to allow Newton's Apple to become the That's Incredible of PBS,” Flatow said in 1983, referring to the NBC info-tainment show. “My role as a kind of gatekeeper is to make sure that every show makes good, sound, scientific points. It may be fun, but it'll be the truth.”

Questions were often selected based on how often they recurred in viewer mail and whether the resulting demonstration would make for compelling television. Kids asked a lot of questions about dinosaurs, while adults were more curious about health and medicine. (The most popular question: Why is the sky blue?) Roughly half of the questions came from viewers; the other half were generated by staffers.

Flatow left the series in 1987 and was replaced by David Heil, the associate director of the Oregon Museum of Science and Industry, following a national talent search. He made his debut by jumping out of an airplane without a parachute. (Fortunately, it was a tandem jump.)

Produced by KTCA, PBS's Minneapolis affiliate, Newton's Apple was supported by the DuPont corporation for most of its run. When that relationship ended in 1990, the show was effectively canceled, only to be revived for another eight seasons when the 3M company agreed to subsidize some of the production costs.

While the show was used as a teaching aid in up to 10 percent of all middle school classrooms in America (PBS issued information packets to be paired with the broadcasts), the secret of its 16 years on the air was that it was watched primarily by older viewers.

In 1992, the Los Angeles Times reported that 80 percent of the show’s audience was 18 years of age or older. The reason, producers said, was that a lot of people stopped being invested in science as part of their school curriculum in junior high and didn't know where else to turn to for answers to the burning questions they had (this was pre-Google, after all). For its role as a remedial learning tool, Newton’s Apple won a Daytime Emmy in 1989 for Outstanding Children’s Series. Unfortunately, there was no category for Outstanding Children's Series Viewed Mostly by Adults.