Forces of Weed Wacker Evil

the rant is mightier than the sword …

I think weed-wackers are the most un-natural power tools ever invented. Everyone I have ever known, myself included, gets stiff as a board after an extended session with one of those damned things.

True, they exercise a whole new set of muscles, an effect we’re definitely familiar with. The product design is the really negligent part. A weed-wacker is a tool with a heavy weight extended criminally far out from the tool’s natural balance point.

The balance point on my old Sears weed wacker was probably about 4″ above the motor housing, almost 3 feet south of the actual handles. This puts enormous forces on the muscular-skeletal system in two planes of motion.

If they put the lower handle on a weed wacker right onto the motor/cutter housing, and the upper handle on the pole about 4″ above that, and left the rest of the arm extend as far up as it does now, this could probably balance the device.

This would work ergonomically if you weighed as much as you do now, and were as strong, but stood only one to two feet tall and had all your legs mounted on extensible arms, like a spider.

Vertically, one’s back, arms, and legs must strain to maintain a constant lifting moment of force, so the damn thing doesn’t hit a rock or scalp the soil bare. Even the cheaper devices, which weigh less, exert a twisting torque which belies the light weight.

Feel strong today? Think you’re up to lifting a single red block brick? Try lifting it at arm’s length with one hand and arm. Hold it extended, still at arm’s length, at eye level — for about five minutes. Pretend you’re sighting some kind of really heavy handgun, so we don’t want to see any vertical or horizontal waver, soldier. Keep that brick suspended motionless in air for the full five minutes, and you’ll really appreciate the forces of physics involved here!

Horizontally, anyone who’s even watched a golf game on TV knows that we don’t just flail the club about with the arms. The swing, the golf stroke, is a coordinated effort. The arms and wrists are relatively locked for most of the swing (hey, you can tell I’m not a golfer), and with most of the work being done by the strongest muscles.

A weed wacker is a golf club with a REALLY heavy head. Swinging it back and forth at a constant height above the ground is tougher than it looks. Legs, hips, back and shoulders should do most of the work. During this time, you also need to figure out the best way of walking forward, backward or sidestepping. This would be somewhat like learning to roller skate with a 40-pound backpack.

I have seen gas-fired designs that put the weight of the motor BEHIND the fulcrum point, the handles at the center, so that they’re relatively well counterbalanced. This takes a hell of a load off the body, so now the act of standing bears the lion’s share of the work in cutter head elevation control.

I’m not saying Ralph Nader was an unqualified positive in the history of American motoring, but maybe we need a Ralph Nader of weed wackers. For folks who get off on conspiracy theories, weed wackers are fertile ground for investigation. Maybe weed wackers are a holdover from the Cold War, a “sleeper” the Bad Guys once planted to cripple America, and demoralize her once-proud resolve. Ow.

copyright ©Alex Forbes June 10, 2001

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