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Pencil Sharpener
A pencil sharpener (or pencil pointer, or in Ireland a parer or topper) is a tool for sharpening a pencil's writing point by shaving away its worn surface. Pencil sharpeners may be operated manually or by an electric motor. It is common for many sharpeners to have a casing around them, which can be removed for emptying the pencil shavings debris into a bin. History Before the development of dedicated pencil sharpeners, a pencil was sharpened by whittling with a knife. The development of pencil sharpeners began in France when a French book from 1822 reported in detail about an invention of Mr. C. A. Boucher (Paris) for the construction of a pencil sharpener. He was working with pantographs and apparently needed a device to precisely sharpen the pencils. The device of Mr. Boucher was technically sensible and functional. His idea was also internationally known and recognized, as shown by corresponding reports in German literature at this time. But Mr. Boucher had not applied a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sharpener With Pencil
A sharpener is a tool for sharpening. It may refer to: *Knife sharpener, a tool for sharpening a knife **Sharpening steel, a tool for sharpening a knife, usually a kitchen knife **Sharpening stone, a tool for sharpening a bladed or edged tool, such a knife *Pencil sharpener, a tool for sharpening a pencil *Sharpening jig, a tool for sharpening a woodworking tool See also *Knifegrinder, a trade or occupation {{disambig Sharpening ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Tangent
In geometry, the tangent line (or simply tangent) to a plane curve at a given point is, intuitively, the straight line that "just touches" the curve at that point. Leibniz defined it as the line through a pair of infinitely close points on the curve. More precisely, a straight line is tangent to the curve at a point if the line passes through the point on the curve and has slope , where ''f'' is the derivative of ''f''. A similar definition applies to space curves and curves in ''n''-dimensional Euclidean space. The point where the tangent line and the curve meet or intersect is called the ''point of tangency''. The tangent line is said to be "going in the same direction" as the curve, and is thus the best straight-line approximation to the curve at that point. The tangent line to a point on a differentiable curve can also be thought of as a '' tangent line approximation'', the graph of the affine function that best approximates the original function at the given point ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Battery (electricity)
An electric battery is a source of electric power consisting of one or more electrochemical cells with external connections for powering electrical devices. When a battery is supplying power, its positive terminal is the cathode and its negative terminal is the anode. The terminal marked negative is the source of electrons. When a battery is connected to an external electric load, those negatively charged electrons flow through the circuit and reach the positive terminal, thus causing a redox reaction by attracting positively charged ions, or cations. Thus, higher energy reactants are converted to lower energy products, and the free-energy difference is delivered to the external circuit as electrical energy. Historically the term "battery" specifically referred to a device composed of multiple cells; however, the usage has evolved to include devices composed of a single cell. Primary (single-use or "disposable") batteries are used once and discarded, as the electrode mat ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
ELM V6 Electric Pencil Sharpener
Elms are deciduous and semi-deciduous trees comprising the genus ''Ulmus'' in the family Ulmaceae. They are distributed over most of the Northern Hemisphere, inhabiting the temperate and tropical-montane regions of North America and Eurasia, presently ranging southward in the Middle East to Lebanon and Israel,Flora of Israel OnlineUlmus minor Mill. , Flora of Israel Online accessdate: July 28, 2020 and across the Equator in the Far East into Indonesia.Fu, L., Xin, Y. & Whittemore, A. (2002). Ulmaceae, in Wu, Z. & Raven, P. (eds) Flora of China'', Vol. 5 (Ulmaceae through Basellaceae). Science Press, Beijing, and Missouri Botanical Garden Press, St. Louis, US. Elms are components of many kinds of natural forests. Moreover, during the 19th and early 20th centuries, many species and cultivars were also planted as ornamental street, garden, and park trees in Europe, North America, and parts of the Southern Hemisphere, notably Australasia. Some individual elms reached great size a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sandpaper
upright=1.35, Sheets of sandpaper with different grit sizes (40 (coarse), 80, 150, 240, 600 (fine)) Sandpaper, also known as coated abrasive or emery paper, is a type of material that consists of sheets of paper or cloth with an abrasive substance glued to one face. In the modern manufacture of these products, sand and glass have been replaced by other abrasives such as aluminium oxide or silicon carbide. It is common to use the name of the abrasive when describing the paper, e.g. "aluminium oxide paper", or "silicon carbide paper". There are many varieties of sandpaper, with variations in the paper or backing, the material used for the grit, grit size, and the bond. Sandpaper is produced in a range of grit sizes and is used to remove material from surfaces, whether to make them smoother (for example, in painting and wood finishing), to remove a layer of material (such as old paint), or sometimes to make the surface rougher (for example, as a preparation for gluing). The grit ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Helix
A helix (; ) is a shape like a cylindrical coil spring or the thread of a machine screw. It is a type of smooth space curve with tangent lines at a constant angle to a fixed axis. Helices are important in biology, as the DNA molecule is formed as two intertwined helices, and many proteins have helical substructures, known as alpha helices. The word ''helix'' comes from the Greek word , "twisted, curved". A "filled-in" helix – for example, a "spiral" (helical) ramp – is a surface called a '' helicoid''. Properties and types The pitch of a helix is the height of one complete helix turn, measured parallel to the axis of the helix. A double helix consists of two (typically congruent) helices with the same axis, differing by a translation along the axis. A circular helix (i.e. one with constant radius) has constant band curvature and constant torsion. The slope of a circular helix is commonly defined as the ratio of the circumference of the circular cylinder that it ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Crank (mechanism)
A crank is an arm attached at a right angle to a rotating shaft by which circular motion is imparted to or received from the shaft. When combined with a connecting rod, it can be used to convert circular motion into reciprocating motion, or vice versa. The arm may be a bent portion of the shaft, or a separate arm or disk attached to it. Attached to the end of the crank by a pivot is a rod, usually called a connecting rod (conrod). The term often refers to a human-powered crank which is used to manually turn an axle, as in a bicycle crankset or a brace and bit drill. In this case a person's arm or leg serves as the connecting rod, applying reciprocating force to the crank. There is usually a bar perpendicular to the other end of the arm, often with a freely rotatable handle or pedal attached. Examples Familiar examples include: Hand-powered cranks * Spinning wheel * Mechanical pencil sharpener * Fishing reel and other reels for cables, wires, ropes, etc. *Starti ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Planetary Gear
An epicyclic gear train (also known as a planetary gearset) is a Reduction drive, gear reduction assembly consisting of two gears mounted so that the center of one gear (the "planet") revolves around the center of the other (the "sun"). A carrier connects the centers of the two gears and rotates, to carry the planet gear(s) around the sun gear. The planet and sun gears mesh so that their pitch circles roll without slip. If the sun gear is held fixed, then a point on the pitch circle of the planet gear traces an epicycloid curve. An epicyclic gear train can be assembled so the planet gear rolls on the inside of the pitch circle of an outer gear ring, or ring gear, sometimes called an ''annulus gear''. Such an assembly of a planet engaging both a sun gear and a ring gear is called a planetary gear train.J. J. Uicker, G. R. Pennock and J. E. Shigley, 2003, ''Theory of Machines and Mechanisms,'' Oxford University Press, New York.B. Paul, 1979, ''Kinematics and Dynamics of Planar Mac ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Razor Blade
A razor is a bladed tool primarily used in the removal of body hair through the act of shaving. Kinds of razors include straight razors, safety razors, disposable razors, and electric razors. While the razor has been in existence since before the Bronze Age (the oldest razor-like object has been dated to 18,000 BC), the most common types of razors currently used are the safety razor and the electric razor. History Razors have been identified from many Bronze Age cultures. These were made of bronze or obsidian and were generally oval-shaped, with a small tang protruding from one of the short ends.Warwickshire County Council: New Prehistoric Archaeology Objects "Even further away in t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Taille Crayon Mécanique-h
The ''taille'' () was a direct land tax on the French peasantry and non-nobles in ''Ancien Régime'' France. The tax was imposed on each household and was based on how much land it held, and was paid directly to the state. History Originally only an "exceptional" tax (i.e. imposed and collected in times of need, as the king was expected to survive on the revenues of the " domaine royal", or lands that belonged to him directly), the ''taille'' became permanent in 1439, when the right to collect taxes in support of a standing army was granted to Charles VII of France during the Hundred Years' War. Unlike modern income taxes, the total amount of the ''taille'' was first set (after the Estates General was suspended in 1484) by the French king from year to year, and this amount was then apportioned among the various provinces for collection. Exempted from the tax were clergy and nobles (except for non-noble lands they held in "pays d'état" ee below, officers of the crown, milita ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
