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A weight machine is an exercise machine used for weight training that uses gravity as the primary source of resistance and a combination of simple machines to convey that resistance to the person using the machine. Each of the simple machines (pulley, lever, wheel, incline) changes the mechanical advantage of the overall machine relative to the weight.
A stack machine—also called a stack or rack—has a set of rectangular plates that are pierced by a vertical bar which has holes drilled in it to accept a pin. [1] Each of the plates has a channel on its underside (or a hole through the middle, as visible in the picture) that aligns with one of the holes. When the pin is inserted through the channel into the hole, all of the plates above the pin rest upon it, and are lifted when the bar rises. The plates below do not rise. This allows the same machine to provide several levels of resistance over the same range of motion with an adjustment that requires very little force to accomplish in itself.
The means of lifting the bar varies. Some machines have a roller at the top of the bar that sits on a lever. When the lever is raised the bar can go up and the roller moves along the lever, allowing the bar to stay vertical. On some machines the bar is attached to a hinge on the lever, which causes swaying in the bar and the plates as the lever goes up and down. On other machines the bar is attached to a cable or belt, which runs through pulleys or over a wheel. The other end of the cable will either be a handle or strap that the user holds or wraps around some body part, or will be attached to a lever, adding further simple machines to the mechanical chain.
Usually, each plate is marked with a number. On some machines these numbers give the actual weight of the plate and those above it. On some, the number gives the force at the user's actuation point with the machine. And on some machines the number is simply an index counting the number of plates being lifted.
The early Nautilus machines were a combination of lever and cable machines. They also had optional, fixed elements such as a chinning bar. Universal Gym Equipment pioneered the multi-station style of machines. [2]
Plate-loaded machines (such as the Smith machine or sled-type leg press) use standard barbell plates instead of captive stacks of plates. They combine a bar-end on which to hang the plates with several simple machines to convey the force to the user.
The plate-loaded machines will often have a very high mechanical advantage, due to the need to make room for large plates over a large range of motion following a path that causes them to converge at one end or the other. Also, the motion will generally not be vertical, and the net resistance is equal to the cosine of the angle at which it is moving relative to vertical.
For example, consider an incline press machine that is a single-lever machine that has the plates halfway up the lever from the handles to the fulcrum, and begins moving the plates at a 45-degree angle from vertical. The lever will provide a leverage advantage of 2:1, and the incline will have an advantage of 1:√2/2, for a net mechanical advantage of (4/√2):1 ≈ 2.8:1. Thus 50 kg (~491 N ) of plates will apply to the user only an equaling weight of 18 kg or a force of ~174 N at the beginning of the motion.
On the other end of the spectrum may be a bent-over-row machine that is designed with the user's grip between the plates and the fulcrum. This amplifies the force needed by the user relative to the weight of the plates.
Mechanical advantage is a measure of the force amplification achieved by using a tool, mechanical device or machine system. The device trades off input forces against movement to obtain a desired amplification in the output force. The model for this is the law of the lever. Machine components designed to manage forces and movement in this way are called mechanisms. An ideal mechanism transmits power without adding to or subtracting from it. This means the ideal machine does not include a power source, is frictionless, and is constructed from rigid bodies that do not deflect or wear. The performance of a real system relative to this ideal is expressed in terms of efficiency factors that take into account departures from the ideal.
A pulley is a wheel on an axle or shaft that is designed to support movement and change of direction of a taut cable or belt, or transfer of power between the shaft and cable or belt. In the case of a pulley supported by a frame or shell that does not transfer power to a shaft, but is used to guide the cable or exert a force, the supporting shell is called a block, and the pulley may be called a sheave or pulley wheel.
A simple machine is a mechanical device that changes the direction or magnitude of a force. In general, they can be defined as the simplest mechanisms that use mechanical advantage to multiply force. Usually the term refers to the six classical simple machines that were defined by Renaissance scientists:
A lever is a simple machine consisting of a beam or rigid rod pivoted at a fixed hinge, or fulcrum. A lever is a rigid body capable of rotating on a point on itself. On the basis of the locations of fulcrum, load and effort, the lever is divided into three types. It is one of the six simple machines identified by Renaissance scientists. A lever amplifies an input force to provide a greater output force, which is said to provide leverage, which is mechanical advantage gained in the system, equal to the ratio of the output force to the input force. As such, the lever is a mechanical advantage device, trading off force against movement.
A cam is a rotating or sliding piece in a mechanical linkage used especially in transforming rotary motion into linear motion. It is often a part of a rotating wheel or shaft that strikes a lever at one or more points on its circular path. The cam can be a simple tooth, as is used to deliver pulses of power to a steam hammer, for example, or an eccentric disc or other shape that produces a smooth reciprocating motion in the follower, which is a lever making contact with the cam. A cam timer is similar, and were widely used for electric machine control before the advent of inexpensive electronics, microcontrollers, integrated circuits, programmable logic controllers and digital control.
A machine is a physical system using power to apply forces and control movement to perform an action. The term is commonly applied to artificial devices, such as those employing engines or motors, but also to natural biological macromolecules, such as molecular machines. Machines can be driven by animals and people, by natural forces such as wind and water, and by chemical, thermal, or electrical power, and include a system of mechanisms that shape the actuator input to achieve a specific application of output forces and movement. They can also include computers and sensors that monitor performance and plan movement, often called mechanical systems.
A bicycle brake reduces the speed of a bicycle or prevents it from moving. The three main types are: rim brakes, disc brakes, and drum brakes.
A block and tackle or only tackle is a system of two or more pulleys with a rope or cable threaded between them, usually used to lift heavy loads.
The term "biceps curl" refers to any of a number of weight training exercises that primarily targets the biceps brachii muscle. It may be performed using a barbell, dumbbell, resistance band, or other equipment.
A bottle opener is a device that enables the removal of metal bottle caps from glass bottles. More generally, it might be thought to include corkscrews used to remove cork or plastic stoppers from wine bottles.
The leg press is a compound weight training exercise in which the individual pushes a weight or resistance away from them using their legs. The term leg press machine refers to the apparatus used to perform this exercise. The leg press can be used to evaluate an athlete's overall lower body strength. It can help to build squat strength. If performed correctly, the inclined leg press can help develop knees to manage heavier free weights, on the other hand, it has the potential to inflict grave injury: the knees could bend the wrong way if they are locked during the exercise.
A cable machine is an item of equipment used in weight training or functional training. It consists of a rectangular, vertically oriented steel frame about 3 metres wide and 2 metres high, with a weight stack attached via a cable and pulley system to one or more handles. The cables that connect the handles to the weight stacks run through adjustable pulleys that can be fixed at any height. This allows a variety of exercises to be performed on the apparatus. One end of the cable is attached to a perforated steel bar that runs down the centre of the weight stack. To select the desired amount of resistance, move the metal pin into the labelled hole in the weight stack. The other end of the cable forms a loop, which allows the user to attach the appropriate handle for the exercise. Most cable machines have a minimum of 20 pounds of resistance in order to counterbalance the weight of the typical attachment.
An elliptical trainer or cross-trainer is a stationary exercise machine used to stair climb, walk, or run without causing excessive pressure to the joints, hence decreasing the risk of impact injuries. For this reason, people with some injuries can use an elliptical to stay fit, as the low impact affects them little. Elliptical trainers offer a non-impact cardiovascular workout that can vary from light to high intensity based on the speed of the exercise and the resistance preference set by the user.
The Chapel Inclined Plane is an inclined plane immediately to the south of Chapel-en-le-Frith, High Peak, Derbyshire. The ground here rises sharply and the inclined plane was built to connect the lower and upper levels of the Peak Forest Tramway, which was built and initially operated by the Peak Forest Canal Company. It opened for trade on 31 August 1796.
A jackscrew, or screw jack, is a type of jack that is operated by turning a leadscrew. It is commonly used to lift moderately and heavy weights, such as vehicles; to raise and lower the horizontal stabilizers of aircraft; and as adjustable supports for heavy loads, such as the foundations of houses.
A garage door is a large door on a garage that opens either manually or by an electric motor. Garage doors are frequently large enough to accommodate automobiles and other vehicles. Small garage doors may be made in a single panel that tilts up and back across the garage ceiling. Larger doors are usually made in several jointed panels that roll up on tracks across the garage ceiling, or into a roll above the doorway. The operating mechanism is spring-loaded or counterbalanced to offset the weight of the door and reduce the human or motor effort required to operate the door. Less commonly, some garage doors slide or swing horizontally. Doors are made of wood, metal, or fiberglass, and may be insulated to prevent heat loss. Warehouses, bus garages and locomotive sheds have larger versions.
An exercise machine is any machine used for physical exercise. These range from simple spring-like devices to computerized electromechanical devices to recirculating-stream swimming pools. Most exercise machines incorporate an ergometer. An ergometer is an apparatus for measuring the work a person exerts while exercising as used in training or cardiac stress tests or other medical tests.
Universal Gym Equipment was an American manufacturer of exercise equipment, in particular weight machines. It was founded by Harold Zinkin in 1957. In 1998, it was acquired by Flexible Flyer. In 2006 it was acquired by Nautilus, Inc. The Universal Gym brand was subsequently discontinued except for a line of selectorized dumbbells.
The compound lever is a simple machine operating on the premise that the resistance from one lever in a system of levers acts as effort for the next, and thus the applied force is transferred from one lever to the next. Almost all scales use some sort of compound lever to work. Other examples include nail clippers and piano keys.
A simple machine that exhibits mechanical advantage is called a mechanical advantage device - e.g.: