Why Are Manhole Covers Round?

iStock
iStock

If you’re in the habit of looking down at your feet as you walk, you may have noticed that most manholes, and their covers, are round. Or perhaps you’ve been in a job interview where your prospective employer asked this question (which apparently happens enough that it was included in the third edition of The Complete Idiot’s Guide to Job Interviews). He wants to know about your ability to think on your feet, and isn’t so much interested in the correct answer, but it is a good question. Of all of the potential shapes for manholes, why was a circle chosen?

There are a number of reasons, according to Larry Scheckel in his book Ask A Science Teacher: 250 Answers to Questions You've Always Had About How Everyday Stuff Really Works. Manholes are round because “it is the best shape to resist the compression of Earth around it.” Round shapes are easier to manufacture than square or rectangular shapes, and because manhole covers are heavy, being round makes them easier to move from place to place (just roll them!). As an added benefit, workers don’t need to line up the covers with any angles, making round covers easy to slip into place.

But perhaps the biggest reason that manhole covers are round is that round covers can’t fall through a circular opening. “For all manholes, there is a ‘lip’ around the rim of the hole, holding up the cover, which means that the underlying hole is smaller than the cover,” Scheckel writes. “A round manhole cover can’t fall through its circular opening, because no matter how you position it, the cover is wider than the hole. But a square, rectangular, or oval manhole cover could fall in if it was inserted diagonally into the hole,” which would be bad news for unobservant pedestrians and drivers alike.

Wayfair’s Fourth of July Clearance Sale Takes Up to 60 Percent Off Grills and Outdoor Furniture

Wayfair/Weber
Wayfair/Weber

This Fourth of July, Wayfair is making sure you can turn your backyard into an oasis while keeping your bank account intact with a clearance sale that features savings of up to 60 percent on essentials like chairs, hammocks, games, and grills. Take a look at some of the highlights below.

Outdoor Furniture

Brisbane bench from Wayfair
Brisbane/Wayfair

- Jericho 9-Foot Market Umbrella $92 (Save 15 percent)
- Woodstock Patio Chairs (Set of Two) $310 (Save 54 percent)
- Brisbane Wooden Storage Bench $243 (Save 62 percent)
- Kordell Nine-Piece Rattan Sectional Seating Group with Cushions $1800 (Save 27 percent)
- Nelsonville 12-Piece Multiple Chairs Seating Group $1860 (Save 56 percent)
- Collingswood Three-Piece Seating Group with Cushions $410 (Save 33 percent)

Grills and Accessories

Dyna-Glo electric smoker.
Dyna-Glo/Wayfair

- Spirit® II E-310 Gas Grill $479 (Save 17 percent)
- Portable Three-Burner Propane Gas Grill $104 (Save 20 percent)
- Digital Bluetooth Electric Smoker $224 (Save 25 percent)
- Cuisinart Grilling Tool Set $38 (Save 5 percent)

Outdoor games

American flag cornhole game.
GoSports

- American Flag Cornhole Board $57 (Save 19 percent)
- Giant Four in a Row Game $30 (Save 6 percent)
- Giant Jenga Game $119 (Save 30 percent)

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The Reason Your Dog Follows You Everywhere

Crew, Unsplash
Crew, Unsplash

Depending on your mood, a dog that follows you everywhere can be annoying or adorable. The behavior is also confusing if you're not an expert on pet behavior. So what is it about the canine companions in our lives that makes them stick by our sides at all times?

Most experts agree on a few different reasons why some dogs are clingy around their owners. One is their pack mentality. Dogs may have been domesticated thousands of years ago, but they still consider themselves to be part of a group like their wild ancestors. When there are no other dogs around, their human family becomes their pack. According to Reader's Digest, this genetic instinct is also what motivates dogs to watch you closely and seek out your physical touch.

The second reason for the behavior has to do with the bond between you and your pet. As veterinarian Dr. Rachel Barrack told the American Kennel Club, puppies as old as 6 months can imprint on their human owners like they would their own mothers. Even older dogs will bond with the humans in their lives who show them care and affection. In these cases, a dog will shadow its owner because it sees them as an object of trust and security.

The last possible explanation for why your dog follows you has more to do with your treatment of them than their natural instincts. A popular training tactic is positive reinforcement—i.e. rewarding a dog with treats, pets, and praise when they perform positive behaviors. The point is to help your dog associate good behaviors with rewards, but after a while, they may start to associate your presence with rewards as well. That means if your dog is following you, they may be looking for treats or attention.

A clingy dog may be annoying, but it usually isn't a sign of a larger problem. If anything, it means your dog sees you in a positive light. So enjoy the extra companionship, and don't be afraid to close the door behind when you need some alone time.