The Physics of Pull-Ups - sunday 2005-04-17 0648 last modified 2005-04-18 1449
Categories: Nerdy, Daily Grind
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I thought of installing a chin-up bar in my room. The immediate question of where to put it pointed directly at a relatively narrow alcove in the back. However, one wall is the kind of false, hollowed wall covering you find in an average suburban home, the kind that necessitates a stud detector to find appropriately sturdy mounting points. The opposing wall is solid brick. So I got to thinking about the mechanics of a bar around a spring that exerted force towards the walls instead of requiring drilling or pounding nails.

It would need to have enough frictional force on the ends to oppose the force of the weight of the bar itself and me along with any other sudden applications of force. Except the surfaces of the opposing walls are uneven and it's likely the smooth, false wall would provide more surface area for friction, whereas the uneven brick wall would provide too many breaks for an equal frictional force on both ends of the bar. Which means there might be a substantial net torque exerted on the bar if I'm not pulling up on the correct part of the bar, which means it and I would fall.

So, anybody know anything about drilling in brick? I guess if one end is mounted well in the brick side, the other end won't need to be fixed in place.



Does the pull-up bar have rubber ends? If so, keep in mind that the uneven surface of the brick isn't a bad thing, in fact, if there's a lot of pressure from the pull up bar horizontally, the rubber will dig into the cracks in the brick and your coefficient of friction probably goes up, I'd think.

Danny Park on April 18, 2005 04:12 PM

are doorways too low?

There are two alternatives if doorways are acceptable (high enough). I believe both models should be removed when not in use, but I break that rule.

The one I have basically consists of two rubber-padded screws that extend outward when you rotate the middle section. So if you do all of your pullups facing the correct direction, your hands tend to rotate the middle section so that the screws attempt to expand outward, pressing against the door frame.

There is a different (perhaps better) model that Joe and Ellen have. It is a little difficult to describe. If you are facing the doorway, most of it is on your side. It reaches through the doorway and up over the frame to support its own weight. On your side of the doorway, it has two pads at a lower elevation that press against the doorway, the same direction that you are facing. As you get a grip on the bar, the force of your weight is directed through the pads into the door frame, in the same direction that you are facing, and also into the top of the door frame, in the opposite direction that you are facing.

a cheng on April 18, 2005 04:37 PM

Or if you insist on drilling...

It's not too difficult to drill into brick. You just have to have a masonry bit. They're easy enough to find at a hardware store or Home Depot. I have a couple.

Bryan Bilyeu on April 18, 2005 06:00 PM

path of least resistance.. as long as you have space

see, this is why i just went with buying a whole tower with a bar and dip handles. =P it also doesn't help that i rent.

joyce L on April 19, 2005 03:56 AM

Thanks for all t...

Thanks for all the input, folks. I think a cheng's first contraption sounds like the least work and an acceptably safe solution for my space. Where can I get one?

Also, if you now do a search on 'friction "pull up" bar,' see who comes up first.

Ryan Lee on April 21, 2005 03:57 PM

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