How Does a Plumb Bob Work?
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What Is a Plumb Bob?
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A plumb bob is a humble tool consisting of a weight at the end of a string. "Plumb" comes from the Latin term "plumbum" for the element lead, indicating a lead slug tied to a string. One end of the string is affixed at a point above the floor or ground, and the weight is allowed to hang free until it stops moving. This shows the user "true vertical." With a plumb bob, anyone can measure or draw a line parallel to Earth's gravity. Plumb bobs often have carefully machined brass or bronze weights with points on the end and cotton or water-resistant nylon string. The point represents the spot directly below the origin of the string. Aside from modern plumb bobs using newer manufactured materials, the plumb bob has not changed in millennia.
Use in Construction
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From surveying to masonry to interior design, plumb bobs are a useful tool for all phases of construction, even in the age of electronic and laser-guided tools. Lasers send a true straight line but do so in any direction; a plumb bob always hangs toward the center of the Earth. Opposing gravity is important in good construction, for the best strength of the structure. Surveyors use the plumb bob for setting up and marking points in uneven terrain. Masons use plum bobs to verify vertical rise of brick constructions. They set up a plum line and follow the string upward as they build. Carpenters use them to measure walls, doorjambs and cabinets. Plum lines can be chalked and plucked, leaving the plumb line on a surface or used merely to mark top and bottom along the vertical plane. Interior designers use them when hanging wallpaper to ensure the seams are true vertical.
Use in Golf
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The same principle applied to the hanging weight on a string tool is applied by many golfers when putting. Dangling the putter by two fingertips, they assess the ball's relation to the cup off of true vertical and use this information to adjust the strength of their put based on the ball's "break." Some golfers swear by this method, and others scoff at its usefulness when faced with an unevenly level green.
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- Photo Credit 08-08-08 © Dave White
