What’s the Difference Between All-Wheel Drive and Four-Wheel Drive?

iStock/PeopleImages
iStock/PeopleImages

As the weather turns nasty, you may start to think more about your car’s transmission—particularly, its ability to get you up and down muddy, snowy, or icy roads. While you may know that two-wheel drive isn’t the best option for driving in harsh weather, other terms are more confusing. Like, for instance, all-wheel drive versus four-wheel drive. Don’t all cars have four wheels (at least when it comes to sedans, SUVs, and other consumer vehicles)? As Jalopnik explains, the difference between all-wheel drive (AWD) and four-wheel drive (4WD) is more than just semantics—and which type you need depends heavily on the kind of driving you do on a regular basis.

When a car manufacturer specifies something as two-, four-, or all-wheel drive, the company is referring to the tires that receive power from the engine. With two-wheel drive, the engine powers either the front axle or the back axle of the car, meaning that the engine is moving only the front tires or the back tires. The other axle is just rolling along. When four-wheel drive (sometimes referred to as 4x4) is engaged, meanwhile, the engine rotates all four wheels. This helps give the car extra traction on slippery surfaces like sand, ice, and gravel—so that even if one set of wheels can’t get traction on a slippery surface, the other wheels might be able to.

The key word there is “engaged.” Traditionally, four-wheel drive means that your car can drive with all four wheels, but you have to manually choose that option. The rest of the time, you’re in two-wheel drive mode. As Ray Magliozzi of NPR’s "Car Talk" once explained to a listener, four-wheel drive is “designed to be engaged when you're already stuck, or in a specific situation where you know you might get stuck—like in snow, sand, or mud. It’s not designed for normal road use, and must be disengaged before you drive on dry, paved roads.”

In all-wheel drive, meanwhile, the car figures out what kind of traction you need all on its own. It has sensors that figure out how much power should go to each wheel to give you the best traction without any input on your part. This is a useful feature for driving in a variety of different conditions, while a dedicated four-wheel drive mode might be better for serious off-roading.

Be warned: There are downsides to all that extra traction. A car’s engine has to work harder to power all four wheels. Those engines are also heavier, which itself takes more power to move. As a result, four-wheel or all-wheel drive cars usually use significantly more fuel than your typical two-wheel drive model.

There are other caveats to this explanation: Full-time four-wheel drive cars do exist, but they differ slightly from all-wheel drive vehicles because of how the two axles of the car move in relation to each other. In four-wheel drive, the front and rear wheels are locked together so they spin at the same rate; in all-wheel drive, the wheels aren’t locked like this—different amounts of power go to the different wheels as needed.

All this said, even if you live somewhere with snowy winters, it doesn’t necessarily mean you should spring for all-wheel drive. If you’re driving a lot in inclement weather—say, if you live in South Dakota or Wyoming rather than sunny Southern California—winter tires may actually be a lot more important than which wheels the engine is powering. Need proof? Watch the video comparison here.

Have you got a Big Question you'd like us to answer? If so, let us know by emailing us at bigquestions@mentalfloss.com.

What is Mercury in Retrograde, and Why Do We Blame Things On It?

NASA
NASA

Crashed computers, missed flights, tensions in your workplace—a person who subscribes to astrology would tell you to expect all this chaos and more when Mercury starts retrograding. For 2020, that means February 17 through March 10; June 18 through July 12; and October 14 through November 3. But according to an astronomer, this common celestial phenomenon is no reason to stay cooped up at home for weeks at a time.

"We don't know of any physical mechanism that would cause things like power outages or personality changes in people," Dr. Mark Hammergren, an astronomer at Chicago's Adler Planetarium, tells Mental Floss. So if Mercury doesn’t throw business dealings and relationships out of whack when it appears to change direction in the sky, why are so many people convinced that it does?

The History of "Mercury in Retrograde"

Mercury retrograde—as it's technically called—was being written about in astrology circles as far back as the mid-18th century. The event was noted in British agricultural almanacs of the time, which farmers would read to sync their planting schedules to the patterns of the stars. During the spiritualism craze of the Victorian era, interest in astrology boomed, with many believing that the stars affected the Earth in a variety of (often inconvenient) ways. Late 19th-century publications like The Astrologer’s Magazine and The Science of the Stars connected Mercury retrograde with heavy rainfall. Characterizations of the happening as an "ill omen" also appeared in a handful of articles during that period, but its association with outright disaster wasn’t as prevalent then as it is today.

While other spiritualist hobbies like séances and crystal gazing gradually faded, astrology grew even more popular. By the 1970s, horoscopes were a newspaper mainstay and Mercury retrograde was a recurring player. Because the Roman god Mercury was said to govern travel, commerce, financial wealth, and communication, in astrological circles, Mercury the planet became linked to those matters as well.

"Don’t start anything when Mercury is retrograde," an April 1979 issue of The Baltimore Sun instructed its readers. "A large communications organization notes that magnetic storms, disrupting messages, are prolonged when Mercury appears to be going backwards. Mercury, of course, is the planet associated with communication." The power attributed to the event has become so overblown that today it's blamed for everything from digestive problems to broken washing machines.

What is Mercury in Retrograde?

Though hysteria around Mercury retrograde is stronger than ever, there's still zero evidence that it's something we should worry about. Even the flimsiest explanations, like the idea that the gravitational pull from Mercury influences the water in our bodies in the same way that the moon controls the tides, are easily deflated by science. "A car 20 feet away from you will exert a stronger pull of gravity than the planet Mercury does," Dr. Hammergren says.

To understand how little Mercury retrograde impacts life on Earth, it helps to learn the physical process behind the phenomenon. When the planet nearest to the sun is retrograde, it appears to move "backwards" (east to west rather than west to east) across the sky. This apparent reversal in Mercury's orbit is actually just an illusion to the people viewing it from Earth. Picture Mercury and Earth circling the sun like cars on a racetrack. A year on Mercury is shorter than a year on Earth (88 Earth days compared to 365), which means Mercury experiences four years in the time it takes us to finish one solar loop.

When the planets are next to one another on the same side of the sun, Mercury looks like it's moving east to those of us on Earth. But when Mercury overtakes Earth and continues its orbit, its straight trajectory seems to change course. According to Dr. Hammergren, it's just a trick of perspective. "Same thing if you were passing a car on a highway, maybe going a little bit faster than they are," he says. "They're not really going backwards, they just appear to be going backwards relative to your motion."

Embedded from GIFY

Earth's orbit isn't identical to that of any other planet in the solar system, which means that all the planets appear to move backwards at varying points in time. Planets farther from the sun than Earth have even more noticeable retrograde patterns because they're visible at night. But thanks to astrology, it's Mercury's retrograde motion that incites dread every few months.

Dr. Hammergren blames the superstition attached to Mercury, and astrology as a whole, on confirmation bias: "[Believers] will say, 'Aha! See, there's a shake-up in my workplace because Mercury's retrograde.'" He urges people to review the past year and see if the periods of their lives when Mercury was retrograde were especially catastrophic. They'll likely find that misinterpreted messages and technical problems are fairly common throughout the year. But as Dr. Hammergren says, when things go wrong and Mercury isn't retrograde, "we don't get that hashtag. It's called Monday."

This piece originally ran in 2018.

Why Are CVS Receipts So Incredibly Long?

cyano66/iStock via Getty Images
cyano66/iStock via Getty Images

If you’ve ever conducted business at one of the nearly 10,000 CVS Pharmacy locations in the United States and count yourself among one of the estimated 62 million members of the store's ExtraCare discount incentive program, you’ve probably been handed a receipt that is more scroll than slip. These transactional documents, which have been known to literally be several feet of thermal paper long and full of merchandise coupons, are often wadded or folded up like a bath towel and handed off to the consumer.

Is this an environmentally mindful practice? And do these coupons really keep people coming back for more?

CVS has stated that the lengthy receipts are intended to demonstrate the value of being an ExtraCare member by offering ExtraCare Rewards, typically a dollar or percentage amount off of a single item or purchase. Some of the receipt's oversized real estate is also taken up by a solicitation to participate in a satisfaction survey. (Though it’s not likely that one of the questions is about the length of the receipt.)

A woman is pictured holding up a CVS receipt
stephen boisvert, Flickr // CC BY 2.0

Simply put, the chain wants to vividly illustrate the benefits of being an ExtraCare member, which also helps the company by allowing them to track your purchase history. The idea is that the Russian novel-length receipt will excite consumers who feel as though a surplus of savings are being delivered right into their hands.

The problem is that the coupons are often quick to expire or can sometimes exclude sale items, registering disappointment when a returning customer presents a slip for $2 off a bar of soap.

You can, of course, opt out of receiving a paper receipt through your ExtraCare account online or via the app, though the process requires a few steps to complete. The coupons will then be sent digitally via your smartphone. Since introducing that paperless option in 2016, the company claims it has saved 3 billion inches of paper that would otherwise have been squeezed into a ball and stuffed into your glove compartment.

Alternately, you can always use it to replace a broken window blind.

Which brings us to the other and possibly most important motivation for those long receipts: Social media engagement. The more people express dismay at those long receipts, the more exposure CVS receives. Considering their 2018 merger with health insurance giant Aetna cost more than $70 billion, some free publicity could come in handy.

Have you got a Big Question you'd like us to answer? If so, let us know by emailing us at bigquestions@mentalfloss.com.

SECTIONS

arrow
LIVE SMARTER