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Slip Joint
A slip joint is a mechanical construction allowing extension and compression in a linear structure. General forms Slip joints can be designed to allow continuous relative motion of two components or it can allow an adjustment, by unclamping from one fixed position, and re-clamping to another. Examples of the latter are tripods, hiking poles, or similar telescoping device. The clamping mechanism is based on a cam, a set screw, or a similar locking mechanism. Slip joints can also be non-telescoping, such as the joints on some older wooden surveyor's levelling rods. These use a joint that keeps the sections offset from each other but able to be slid together for transport. Examples of continuous slip joints are given below. Special purpose slip joints Civil engineering Slip joints in large structures are used to allow the independent motion of large components while enabling them to be joined in some way. For example, if two tall buildings are to be joined with a pedestria ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Tripod (photography)
In photography, a tripod is a portable device used to support, stabilize and elevate a camera, a flash unit, or other videographic or observational/measuring equipment. All photographic tripods have three legs and a mounting head to couple with a camera. The mounting head usually includes a thumbscrew that mates to a female-threaded receptacle on the camera, as well as a mechanism to be able to rotate and tilt the camera when it is mounted on the tripod. Tripod legs are usually made to telescope, in order to save space when not in use. Tripods are usually made from aluminum, carbon fiber, steel, wood or plastic. Usage Tripods are used for both still and motion photography to prevent camera movement. They are necessary when slow-speed exposures are being made, or when lenses of extreme focal length are used, as any camera movement while the shutter is open will produce a blurred image. In the same vein, they reduce camera shake, and thus are instrumental in achieving max ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hiking Pole
Trekking poles (also known as hiking poles, hiking sticks or walking poles) are a common hiking accessory that function to assist walkers with their rhythm, to provide stability, and reduce strain on joints on rough terrain. Description When in use, modern trekking poles resemble ski poles as they have many features in common, such as baskets at the bottom to prevent the pole sinking through unstable surfaces, and rubber-padded handles and wrist straps to strengthen holding grip. Their maximum length is usually 135 cm (54 inches), however, unlike ski poles, they are often made in two or three sections and can be extended and retracted as necessary for use and collapsed for storage or transport. When fully retracted it may be possible to attach them to a backpack. Some poles come with spring-loaded sections to aid walking under normal conditions and to reduce wrist strain, but such devices may only add unwanted weight and noise to the poles. They are usually made from lightweight a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Telescoping (mechanics)
Telescoping in mechanics describes the movement of one part sliding out from another, lengthening an object (such as a telescope or the lift arm of an aerial work platform) from its rest state. In modern equipment this can be achieved by a hydraulics, but pulleys are generally used for simpler designs such as extendable ladders & amateur radio Amateur radio, also known as ham radio, is the use of the radio frequency spectrum for purposes of non-commercial exchange of messages, wireless experimentation, self-training, private recreation, radiosport, contesting, and emergency commu ... antennas. See also * Telescopic cylinder Mechanics Simple machines {{classicalmechanics-stub ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Set Screw
In American English, a set screw is a screw that is used to secure an object, by pressure and/or friction, within or against another object, such as fixing a pulley or gear to a shaft. A set screw is normally used without a nut (which distinguishes it from a bolt), being screwed instead in a threaded hole drilled in only one of the two objects to be secured. A set screw is often headless and threaded along its entire length, so that it will sit entirely inside that hole; in which case it may be called a grub screw or blind screw. Once fully and firmly screwed into the first object, the projecting tip of the set screw presses hard against the second object, acting like a clamp. The second object may have a machined detent (recess) to ensure that it cannot slide under the tip of the screw. On a shaft, this may be simply a flattened area. A set screw may have any type of drive, such as hex or square head, slot, or recessed --- cross (Phillips), hex (Allen), star (Torx), or sq ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Levelling Rod
Levelling or leveling (American English; see spelling differences) is a branch of surveying, the object of which is to establish or verify or measure the height of specified points relative to a datum. It is widely used in geodesy and cartography to measure vertical position with respect to a vertical datum, and in construction to measure height differences of construction artifacts. Optical levelling Optical levelling, also known as spirit levelling and differential levelling, employs an ''optical level'', which consists of a precision telescope with crosshairs and stadia marks. The cross hairs are used to establish the level point on the target, and the stadia allow range-finding; stadia are usually at ratios of 100:1, in which case one metre between the stadia marks on the levelling staff represents 100metres from the target. The complete unit is normally mounted on a tripod, and the telescope can freely rotate 360° in a horizontal plane. The surveyor adjusts the instrume ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Skyway
A skyway, skybridge, skywalk, or sky walkway is an elevated type of pedway connecting two or more buildings in an urban area, or connecting elevated points within mountainous recreational zones. Urban skyways very often take the form of enclosed or covered footbridges that protect pedestrians from the weather. Open-top modern skyways in mountains now often have glass bottoms. Sometimes enclosed urban skywalks are made almost totally from glass, including ceilings, walls and floors. Also, some urban skyways function strictly as linear parks designed for walking. In North America skyways are usually owned by businesses, and are therefore not public spaces (compare with sidewalk). However, in Asia, such as Bangkok's and Hong Kong's skywalks, they are built and owned separately by the city government, connecting between privately run rail stations or other transport with their own footbridges, and run many kilometers. Skyways usually connect on the first few floors above the groun ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ground Motion
Ground motion is the movement of the earth's surface from earthquakes or explosions. Ground motion is produced by seismic waves that are generated by sudden slip on a fault or sudden pressure at the explosive source and travel through the earth and along its surface. This can be due to natural events, such as earthquakes and volcanic eruptions, or human activities, such as the detonation of nuclear weapons. There are two main types of seismic waves: body waves and surface waves. Body waves travel through the interior of the earth, while surface waves travel along the earth's surface. Ground motion is typically caused by surface waves, which are the most destructive type of seismic waves. Ground motion is measured using a seismometer A seismometer is an instrument that responds to ground noises and shaking such as caused by earthquakes, volcanic eruptions, and explosions. They are usually combined with a timing device and a recording device to form a seismograph. The outpu . ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Earthquake
An earthquake (also known as a quake, tremor or temblor) is the shaking of the surface of the Earth resulting from a sudden release of energy in the Earth's lithosphere that creates seismic waves. Earthquakes can range in intensity, from those that are so weak that they cannot be felt, to those violent enough to propel objects and people into the air, damage critical infrastructure, and wreak destruction across entire cities. The seismic activity of an area is the frequency, type, and size of earthquakes experienced over a particular time period. The seismicity at a particular location in the Earth is the average rate of seismic energy release per unit volume. The word ''tremor'' is also used for non-earthquake seismic rumbling. At the Earth's surface, earthquakes manifest themselves by shaking and displacing or disrupting the ground. When the epicenter of a large earthquake is located offshore, the seabed may be displaced sufficiently to cause a tsunami. Earthquak ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Viscosity
The viscosity of a fluid is a measure of its resistance to deformation at a given rate. For liquids, it corresponds to the informal concept of "thickness": for example, syrup has a higher viscosity than water. Viscosity quantifies the internal frictional force between adjacent layers of fluid that are in relative motion. For instance, when a viscous fluid is forced through a tube, it flows more quickly near the tube's axis than near its walls. Experiments show that some stress (such as a pressure difference between the two ends of the tube) is needed to sustain the flow. This is because a force is required to overcome the friction between the layers of the fluid which are in relative motion. For a tube with a constant rate of flow, the strength of the compensating force is proportional to the fluid's viscosity. In general, viscosity depends on a fluid's state, such as its temperature, pressure, and rate of deformation. However, the dependence on some of these properties ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Shock Absorber
A shock absorber or damper is a mechanical or hydraulic device designed to absorb and damp shock impulses. It does this by converting the kinetic energy of the shock into another form of energy (typically heat) which is then dissipated. Most shock absorbers are a form of dashpot (a damper which resists motion via viscous friction). Description Pneumatic and hydraulic shock absorbers are used in conjunction with cushions and springs. An automobile shock absorber contains spring-loaded check valves and orifices to control the flow of oil through an internal piston (see below). One design consideration, when designing or choosing a shock absorber, is where that energy will go. In most shock absorbers, energy is converted to heat inside the viscous fluid. In hydraulic cylinders, the hydraulic fluid heats up, while in air cylinders, the hot air is usually exhausted to the atmosphere. In other types of shock absorbers, such as electromagnetic types, the dissipated energy ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Expansion Joint
An expansion joint, or movement joint, is an assembly designed to hold parts together while safely absorbing temperature-induced expansion and contraction of building materials, and vibration, or to allow movement due to ground settlement or seismic activity. They are commonly found between sections of buildings, bridges, sidewalks, railway tracks, piping systems, ships, and other structures. Building faces, concrete slabs, and pipelines expand and contract due to warming and cooling from seasonal variation, or due to other heat sources. Before expansion joint gaps were built into these structures, they would crack under the stress induced. Bridge expansion joints Bridge expansion joints are designed to allow for continuous traffic between structures while accommodating movement, shrinkage, and temperature variations on reinforced and prestressed concrete, composite, and steel structures. They stop the bridge from bending out of place in extreme conditions, and also allow en ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Bellows
A bellows or pair of bellows is a device constructed to furnish a strong blast of air. The simplest type consists of a flexible bag comprising a pair of rigid boards with handles joined by flexible leather sides enclosing an approximately airtight cavity which can be expanded and contracted by operating the handles, and fitted with a valve allowing air to fill the cavity when expanded, and with a tube through which the air is forced out in a stream when the cavity is compressed. xford English Dictionary, 2nd ed: bellows/ref> It has many applications, in particular blowing on a fire to supply it with air. The term "bellows" is used by extension for a flexible bag whose volume can be changed by compression or expansion, but not used to deliver air. For example, the light-tight (but not airtight) bag allowing the distance between the lens and film of a folding photographic camera to be varied is called a bellows. Etymology "Bellows" is only used in plural. The Old English na ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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