Jewish World Review August 12, 2003 / 14 Menachem-Av, 5763

Jeff Elder

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Consumer Reports


Why do wheels appear to turn backward on film?; showdown over high noon


http://www.jewishworldreview.com | Q: I've been having the biggest argument with someone in town. He says midnight is 12 p.m., and I say it's 12 a.m. Who's right? - Susan Harrington

A: Susan, y'all must have a lotta time on your hands.

Interesting thing about your High Noon (or midnight) standoff is, you're both wrong.

Official timekeepers such as the U.S. Naval Observatory and the Royal Observatory in Greenwich, England, tell us that, technically, the exact moments of midnight and noon are neither a.m. nor p.m.

The abbreviations a.m. and p.m. stand for the Latin ante meridiem (before midday) and post meridiem (after midday).

Noon can't technically be p.m. if p.m. means "after midday." Noon is midday. It's like asking if the equator is in the northern or southern hemisphere. It's in neither.

The period between midnight and noon is a.m. The period between noon and midnight is p.m. But noon and midnight themselves are neither a.m. nor p.m. Even one nano-second on either side of these markers can take the two-letter designations a.m. and p.m. But straight-up noon and midnight are their own entities, strictly speaking.

But there's also a practical side to this argument. Many digital clocks and computers (and we all know how ubiquitous and powerful these contraptions are) can't handle the concept of noon and midnight. They need to assign the a.m. and p.m. designations to all times, including 12:00 and no seconds. At 11:59 and 59 seconds at night, digital clocks say it's p.m. A second later, at midnight, digital clocks and computers say it's a.m. A similar switchover happens at noon. For that reason, many people think of midnight as 12 a.m. and noon as 12 p.m.

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Q: Why do wheels appear to turn backward on film? I have wondered about this since days of watching Westerns in the 1950s with covered wagons, and still see this today on auto commercials. - Anne

A: Anne, the backward wagon wheel is one of the great mysteries of Western movies.

Wheels sometimes appear to turn backward on film due to an optical illusion called a strobe effect. See, a movie is a series of still pictures that flash on and off 24 times a second. That's fast enough for your brain to think the motion is continuous. Your eyes can't see the separate frames. But it's not fast enough to capture true continuous motion.

So wheels do weird things on film. Rolling wheels can even appear stationary. Suppose a wheel is rotating exactly one revolution in ݦth of a second. The camera snaps a frame as the spokes reach exactly the same position they were in one frame earlier. Then the wheel rotates again and the camera snaps another frame. The wheel looks stationary.

If the wheel turns a little faster than this, the spokes seem to slowly move forward because the spokes move a little past where they were in the last frame. If the wheel turns a little slower than a full revolution each frame, the spokes appear to move slowly backward.

SOURCES: Arizona State University, UNC Chapel Hill Department of Statistics

___

QUICK QUIZ

Reveal your criminal minds on crooks real and fictitious.

1. In Victor Hugo's "Les Miserables," what does sympathetic character Jean Valjean steal, in a crime that changes his life?

2. Who was notorious for her four sons and seven Tommy guns?

3. What role was played by Julie Newmar, Lee Meriwether, Eartha Kitt and Michelle Pfeiffer?

4. What was Robert Stroud better known as?

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ANSWERS

1. A loaf of bread

2. Ma Barker

3. Catwoman, Batman's purrrfect (not to mention sexy as all get-out) nemesis

4. The Birdman of Alcatraz

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Jeff Elder is a columnist for The Charlotte Observer. Comment or try to stump him by clicking here.

Up


08/07/03: Wood'n you know it? Money doesn't grow on trees; all we are is dust in the wind
08/05/03: Where have you gone, Calvin, Opus and Cow?; fine feathered friend pecking on itself
07/31/03: How a dashing hero became a notorious traitor
07/29/03: Little red caboose rolling outta sight; From my 'I'll be a monkey's uncle' file
07/24/03: Road scholar: A lesson on asphalt; when identical twins marry
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