science

String trimmer

String trimmer is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand String trimmer rather than just read about it. In short: A string trimmer, also known by the portmanteau strimmer and the trademarks Weedwacker, Weed Eater and Whipper Snipper, is a garden power tool for cutting grass, small weeds, and groundcover. Instead of a blade, it uses a whirling monofilament line which protrudes from a rotating spindle at the end of a long shaft topped by a gasoline engine or electric motor.

Key takeaways

String trimmer belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect String trimmer to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of String trimmer from memory before moving on to harder problems.

Reference excerpt

A string trimmer, also known by the portmanteau strimmer and the trademarks Weedwacker, Weed Eater and Whipper Snipper, is a garden power tool for cutting grass, small weeds, and groundcover. Instead of a blade, it uses a whirling monofilament line which protrudes from a rotating spindle at the end of a long shaft topped by a gasoline engine or electric motor. String trimmers are commonly used for cutting low foliage near obstacles or on steep or irregular terrain. Most professional-grade line trimmers take brush cutter attachments for denser vegetation.

History The string trimmer was invented in the early 1970s by George Ballas of Houston, Texas, who conceived the idea while watching the revolving action of the cleaning brushes in an automatic car wash. His first trimmer was made by attaching pieces of heavy-duty fishing line to a tin can bolted to an edger. Ballas developed this into what he called the "Weed Eater", since it chewed up the grass and weeds around trees. The word "strimmer" is a trade name of Black+Decker and is a registered trademark in the United Kingdom, but it is often used as a generic for any string trimmer. From it has been backformed the colloquial verb "to strim".

Design

A string trimmer works on the principle that a line spun fast enough on its center stiffens by centrifugal force; the faster the hub turns, the more rigid the line. Even round-section nylon line is able to cut grass and slight, woody plants quite well. Some monofilament lines designed for more powerful cutters have an extruded shape, like a star, that helps the line slash the material being cut; the line is thus able to cut quite large woody plants (small shrubs) or at least girdle them effectively. These lines make solid disks less necessary for tough jobs. The line is hand-wound onto a reel before the job is started, leaving both ends extending from the reel housing. The motor turns the reel and the line extends horizontally while the operator swings the trimmer about where the plants are to be trimmed. The operator controls the height at which cutting takes place and can trim down to ground level quite easily.

As the line is worn—or breaks off—a bump feed string trimmer, the operator knocks the reel on the ground so a release mechanism allows some of the line in the reel to replace the spent portion. Newer models "auto-feed", where a small cutter ensures the exposed length does not exceed what can be swung effectively. Newly extended line operates more effectively because of its heavier weight and surface effects. The speed of the spinning hub is controlled by a trigger-activated throttle on the handle.

A fixed-line string trimmer has a trimmer head that takes pre-cut line inserts. There is no wound spool of line in the trimmer head; the user instead feeds the pre-cut line in to the appropriate slots, making the trimmer easier to feed line into and troubleshoot than a bump feed system. For vertical cutting the whole machine can be tilted or some trimmers allow the head to be adjusted at different angles. String trimmers powered by an internal combustion engine have the engine on the opposite end of the shaft from the cutting head, while electric string trimmers typically have an electric motor in the cutting head, but there are other arrangements, such as where the trimmer is connected to heavy machinery and powered by a hydraulic motor. The head contains a safety shield on the user side and a rotating hub which may also be called a head or spool. Disadvantages of a gasoline-powered string trimmer include its greater weight, the need to refuel, and the significant vibration that carries throughout the device, both of which interfere with its maneuverability and contribute to muscle fatigue. Advantages include complete mobility and higher maximum power. Large trimmers, used for cutting thick roadside grass and weeds in large areas, are both heavier and more powerful. Some are fitted with a harness to spread weight onto the shoulders. Often referred to as brush cutters, these often mount straight or circular metal blades instead of monofilament line.

Accessories

Many string trimmers allow the hub, the head or the lower part of the shaft to be replaced with accessories. Common accessories include:

metal or plastic blades a small chainsaw a toothed hedge trimmer a cultivator Quick-release shafts are offered on many newer models which do not require any tools to switch in accessories.

Power and emissions

Gasoline-engine powered trimmers usually have a minimum of 21 cc (21 cm3; 1.3 cu in) displacement motors. At this size, they can easily turn 2-millimetre (0.079 in) line, and some have nylon blades as accessories to the line-reel. A 32 cc (32 cm3; 2.0 cu in) engine can swing a 2.75 mm (0.108 in) line and often has metal-blade accessories. Most trimmers use single-cylinder engines (particularly two-stroke) and require gasoline mixed with oil. Due to pollution laws four stroke engines are becoming more popular, particularly in the commercial market. Manufacturers include Honda, MTD and Craftsman. Companies such as John Deere carry low-emission two-stroke engine trimmers. Stihl manufactures a hybrid four-stroke engine trimmer that still requires oil to be pre-mixed into the fuel. Electrically powered string trimmers produce zero emissions at the point of use, are more efficient, and eliminate risks from spilled gasoline. However, they are typically less powerful and robust than gasoline-powered units; normally they are limited to 2.5 mm (0.098 in) maximum diameter nylon because of their lower power output (400 to about 1200 watts). Gas-powered string trimmers are not regulated to have emission-capturing technology in the USA. Mains-powered string trimmers have the advantage of being very light, easy to maneuver and easy-to-operate. However, both the power cord and total cord length limit them. Recharge time for a battery model using small or large sealed lead acid, nickel metal hydride, or lithium-ion batteries is typically several hours; some models offer a quick-charge option of as little as half an hour, or a removable battery pack. Propane-powered string trimmers were also manufactured by Lehr.

… excerpt ends here. Continue reading the full article.

Illustrations

Worked examples

Example 1 — a first encounter with String trimmer

Start with the simplest possible case. Write down what String trimmer claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to String trimmer before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about String trimmer ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of String trimmer

In research: String trimmer appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses String trimmer in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: String trimmer is common in secondary-school and first-year university syllabi. It links to neighbouring topics American inventions, Gardening tools, Habitat management equipment and methods, so understanding it makes those chapters shorter.
In everyday life: Look for String trimmer outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study String trimmer in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what String trimmer means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain String trimmer out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is String trimmer in simple terms?

Why does String trimmer matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study String trimmer?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on String trimmer.