What David Letterman’s Velcro Suit Stunt Has to Do with Earthquake Preparedness

 

Talk show host David Letterman donned a Velcro jumpsuit then launched himself off a trampoline at a Velcro wall…and “splat.” He stuck right to the wall. It’s one of his most famous stunts. But what does Letterman’s Velcro suit stunt tell us about earthquake preparedness?

Imagine how safe your house would be if all of your walls and furniture were covered in Velcro. You could just push your cabinets and bookshelves against your walls and voilà, they’d all be securely fastened. It wouldn’t be limited to just your furniture, you could secure everything. Think of how easy it would be to hang pictures. No hammer, stud finder or nails needed. Just press your Velcro-backed frames against your wall and they’d stick right where you put them. Plus, you could move them whenever you wanted without having to fill in any nail holes. Then there’s your kids. Are they still chasing the cat around the house at top speed? You could just…on second thought, uhm, you should probably pass on Velcroing the kids…

Ok, so that sort of Velcro House of Tomorrow it isn’t practical. That much Velcro would cost a fortune…and you couldn’t just paint it when you wanted to change the color. However, you really can use Velcro to help secure your home from earthquakes. You don’t need an entire house full of it, either. Instead you can use just a few square inches of it in the form of Velcro earthquake safety straps to secure your furniture. Totally Unprepared co-host Ron Haralson shows us how to install them, and it is super easy.

But can such little pieces of Velcro actually hold a bookshelf in an earthquake? Yes, yes they can. Totally Unprepared’s Susan Jekarl put earthquake safety straps to the test on a powerful earthquake shake table:

So What Does Letterman Have to Do with This? (Warning: Cool Science Stuff)

David Letterman’s Velcro suit shows how strong hook and loop fasteners are against sliding apart (shear force). When Letterman launched himself at the Velcro wall and stuck, all the Velcro hooks and loops were engaged at the same time. The force of gravity trying to pull him straight down off the wall pulls on all the hooks and loops at the same time. Individually the hooks and loops are pathetically weak but when they resist force together they are powerful–the hook and loop version of “I am Spartacus.” This same principle applies to the Velcro earthquake safety straps. They are attached to the furniture and the wall so that they hold against shear force. We tested them with a small hand scale and the shear strength was literally off the 70 pound limit of our scale. In spite of that, the hook and loop fasteners are easy to pull apart by peeling–you can do it with just your pinky. That’s because when you peel apart hook and loop fasteners, you are pulling them apart just a few hooks at at time. To help prevent that, the safety straps have a clever little flap that resists peeling.

Why Velcro earthquake safety straps can hold during an earthquake: shear strength. Pulling Velcro appart a few hooks at a time, that's why it is easy to peel Velcro appart. How an extra flap gives this Velcro earthquake safety strap extra resistance to peeling.
Posted in Disaster v. Preparedness

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