Information about Pulley
For the band, see Pulley (band). For the village, see Pulley, Shropshire.
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Pulleys on a ship. In this context, pulleys are usually known as blocks.
A pulley (also called a sheave or block) is a wheel with a groove between two flanges around its circumference. The groove normally locates a rope, cable or belt. Pulleys are used to change the direction of an applied force, transmit rotational motion, or realize a mechanical advantage in either a linear or rotational system of motion.
Rope and Pulley Systems
Rope and pulley systems (the rope may be a light line or a strong cable) are characterized by the use of a single rope transmitting a linear motive force (in tension) to a load through one or more pulleys for the purpose of pulling the load (often against gravity.) They are often included in the list of simple machines. In a system of a single rope and pulleys, the mechanical advantage gained is ideally the number of pulleys in the system (if one pulley is used only to change the direction of the load). The tension in the rope is reduced by the mechanical advantage, while the distance (that is, the length of rope) is increased by the same proportion. Since a slender cable is more easily managed than a fat one (albeit shorter and stronger), pulley systems are often the preferred method of applying mechanical advantage to the pulling force of a winch (as can be found in a lift crane).In practice, the more pulleys there are, the less efficient a system is. This is due to friction in the system where cable meets pulley and in the rotational mechanism of each pulley.
It is not recorded when or by whom the pulley was first developed. It is believed however that Archimedes developed the first documented block and tackle pulley system, as recorded by Plutarch. Plutarch reported that Archimedes moved an entire warship, laden with men, using compound pulleys and his own strength.
Types of Systems
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- Fixed A fixed or class 1 pulley has a fixed axle. That is, the axle is "fixed" or anchored in place. A fixed pulley is used to change the direction of the force on a rope (called a belt). A fixed pulley has a mechanical advantage of 1. A mechanical advantage of one means that the force is equal on both sides of the pulley and there is no multiplication of force
- Movable A movable or class 2 pulley has a free axle. That is, the axle is "free" to move in space. A movable pulley is used to multiply forces. A movable pulley has a mechanical advantage of 2. That is, if one end of the rope is anchored, pulling on the other end of the rope will apply a doubled force to the object attached to the pulley.
- Compound A compound pulley is a combination fixed and movable pulley system.
- Block and tackle - A block and tackle is a compound pulley where several pulleys are mounted on each axle, further increasing the mechanical advantage.
How it Works
Diagram 1 - A basic equation for a pulley: In equilibrium, the force F on the pulley axle is equal and opposite to the sum of the tensions in each line leaving the pulley, and these tensions are equal. | Diagram 2 - A simple pulley system - a single movable pulley lifting a unit weight. The tension in each line is half the unit weight, yielding an advantage of 2. | Diagram 2a - Another simple pulley system similar to diagram 2, but in which the lifting force is redirected downward. | ) A practical compound pulley corresponding to diagram 2a. |
The simplest theory of operation for a pulley system assumes that the pulleys and lines are weightless, and that there is no energy loss due to friction. It is also assumed that the lines do not stretch.
In equilibrium, the total force on the pulley must be zero. This means that the force on the axle of the pulley is shared equally by the two lines looping through the pulley. The situation is schematically illustrated in diagram 1. For the case where the lines are not parallel, the tensions in each line are still equal, but now the vector sum of all forces is zero.
A second basic equation for the pulley follows from the conservation of energy: The product of the weight lifted times the distance it is moved is equal to the product of the lifting force (the tension in the lifting line) times the distance the lifting line is moved. The weight lifted divided by the lifting force is defined as the advantage of the pulley system.
It is important to notice that a system of pulleys does not change the amount of work done. The work is given by the force times the distance moved. The pulley simply allows trading force for distance: you pull with less force, but over a longer distance.
In diagram 2, a single movable pulley allows a unit weight to be lifted with only half the force needed to lift the weight without assistance. The total force needed is divided between the lifting force (red arrow) and the "ceiling" which is some immovable object (such as the earth). In this simple system, the lifting force is directed in the same direction as the movement of the weight. The advantage of this system is 2. Although the force needed to lift the unit weight is only half of the unit weight, we will need to draw a length of rope that is twice the distance that the weight is lifted, so that the total amount of work done (Force x distance) remains the same.
A second pulley may be added as in diagram 2a, which simply serves to redirect the lifting force downward, it does not change the advantage of the system.
Diagram 3 - A simple compound pulley system - a movable pulley and a fixed pulley lifting a unit weight. The tension in each line is one third the unit weight, yielding an advantage of 3. | Diagram 3a - A simple compound pulley system - a movable pulley and a fixed pulley lifting a unit weight, with an additional pulley redirecting the lifting force downward. The tension in each line is one third the unit weight, yielding an advantage of 3. | Diagram 4a - A more complicated compound pulley system. The tension in each line is one quarter of the unit weight, yielding an advantage of 4. An additional pulley redirecting the lifting force has been added. | ) Figure 4b - A practical block and tackle pulley system corresponding to diagram 4a. Note that the axles of the fixed and movable pulleys have been combined. |
The addition of a fixed pulley to the single pulley system can yield an increase of advantage. In diagram 3, the addition of a fixed pulley yields a lifting advantage of 3. The tension in each line is ⅓ the unit weight, and the force on the axles of each pulley is ⅔ of a unit weight. As in the case of diagram 2a, another pulley may be added to reverse the direction of the lifting force, but with no increase in advantage. This situation is shown in diagram 3a.
This process can be continued indefinitely for ideal pulleys with each additional pulley yielding a unit increase in advantage. For real pulleys friction among rope and pulleys will increase as more pulleys are added to the point that no advantage is possible. It puts a limit for the number of pulleys we can use in practice. The above pulley systems are known collectively as block and tackle pulley systems. In diagram 4a, a block and tackle system with advantage 4 is shown. A practical implementation in which the connection to the ceiling is combined and the fixed and movable pulleys are encased in single housings is shown in figure 4b.
Other pulley systems are possible, and some can deliver an increased advantage with fewer pulleys than the block and tackle system. The advantage of the block and tackle system is that each pulley and line is subjected to equal tensions and forces. Efficient design dictates that each line and pulley be capable of handling its load, and no more. Other pulley designs will require different strengths of line and pulleys depending on their position in the system, but a block and tackle system can use the same line size throughout, and can mount the fixed and movable pulleys on a common axle.
Belt and Pulley Systems
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belt and pulley system
A belt and pulley system is characterized by two or more pulleys in common to a belt. This allows for mechanical power, torque, and speed to be transmitted across axes and, if the pulleys are of differing diameters, a mechanical advantage to be realized.
A belt drive is analogous to that of a chain drive, however a belt sheave may be smooth (devoid of discrete interlocking members as would be found on a chain sprocket, spur gear, or timing belt) so that the mechanical advantage is given by the ratio of the pitch diameter of the sheaves only (one is not able to count 'teeth' to determine gear ratio).
Belt and pulley systems are systems that can be very efficient, with stated efficiencies up to 98%.
See also
Pulley is a Southern California punk outfit that made its debut in 1996. The band is known for straight-forward, hard-edged melodic punk. Pulley was formed upon vocalist Scott Radinsky's departure from Ten Foot Pole, brought about by that band's desire for a singer with a full-time
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Pulley is a small village on the southern edge of Shrewsbury in Shropshire, England. It is located between Shrewsbury and Bayston Hill. The A5 Shrewsbury by-pass cuts through the area.
To the north is the Shrewsbury suburb of Meole Brace.
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To the north is the Shrewsbury suburb of Meole Brace.
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wheel is a circular device capable of rotating on its axis, facilitating movement or transportation or performing labour in machines. A wheel together with an axle overcomes friction by facilitating motion by rolling. Common examples are found in transport applications.
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Tongue and groove (sometimes T&G) is a method of fitting similar objects together, edge to edge, used mainly with wood: flooring, parquetry, panelling, etc. Before plywood became more common, tongue and groove boards were also used for sheathing buildings and to
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The circumference is the distance around a closed curve. Circumference is a kind of perimeter.
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Circle
The circumference of a circle can be calculated from its diameter using the formula:..... Click the link for more information.
rope (IPA: /rəʊp/) is a length of fibers, twisted or braided together to improve strength for pulling and connecting. It has tensile strength but is too flexible to provide compressive strength (i.e.
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cable is one or more wires or optical fibers bound together, typically in a common protective jacket or sheath. The individual wires or fibers inside the jacket may be covered or insulated. Combination cables may contain both electrical wires and optical fibers.
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In physics, force is an action or agency that causes a body of mass m to accelerate. It may be experienced as a lift, a push, or a pull. The acceleration of the body is proportional to the vector sum of all forces acting on it (known as net force or resultant force).
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In physics and engineering, mechanical advantage (MA) is the factor by which a mechanism multiplies the force put into it. Following are simple machines where the mechanical advantage is calculated.
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- The beam shown is in static equilibrium around the fulcrum.
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simple machine is any device that only requires the application of a single force to work. Work is done when a force is applied and results in movement over a set distance. The work done is the product of the force and the distance.
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winch is a mechanical device that is used to wind up a rope or wire rope (also called "cable"). In its simplest form it consists of a spool and attached crank. The spool can also be called the winch drum.
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Friction is the force of two surfaces in contact. It is not a fundamental force, as it is derived from electromagnetic forces between atoms. When contacting surfaces move relative to each other, the friction between the two objects converts kinetic energy into thermal energy, or
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Archimedes of Syracuse (Greek: Άρχιμήδης c. 287 BC – c. 212 BC) was an ancient Greek mathematician, physicist and engineer.
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block and tackle[1] is a system of two or more pulleys with a rope or cable threaded between them, usually used to lift or pull heavy loads.
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Overview
Although used in many situations, they are especially common on boats and sailing ships, where motorized aids..... Click the link for more information.
Plutarch
Mestrius Plutarchus
Πλούταρχο?
Parallel Lives, Amyot translation, 1565
Born: Circa 46 AD
Chaeronea, Boeotia
Died: Circa 120 AD
Delphi, Phocis
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Mestrius Plutarchus
Πλούταρχο?
Parallel Lives, Amyot translation, 1565
Born: Circa 46 AD
Chaeronea, Boeotia
Died: Circa 120 AD
Delphi, Phocis
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axle is a central shaft for a rotating wheel or gear. In some cases the axle may be fixed in position with a bearing or bushing sitting inside the hole in the wheel or gear to allow the wheel or gear to rotate around the axle.
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Belt is a looped strip of flexible material, used to mechanically link two or more rotating shafts. They may be used as a source of motion, to efficiently transmit power, or to track relative movement.
Belts are looped over pulleys.
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Belts are looped over pulleys.
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In physics and engineering, mechanical advantage (MA) is the factor by which a mechanism multiplies the force put into it. Following are simple machines where the mechanical advantage is calculated.
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- The beam shown is in static equilibrium around the fulcrum.
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Tension is a reaction force applied by a stretched string (rope or a similar object) on the objects which stretch it. The direction of the force of tension is parallel to the string, towards the string.
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In physics, mechanical work is the amount of energy transferred by a force. Like energy, it is a scalar quantity, with SI units of joules. Heat conduction is not considered to be a form of work, since there is no macroscopically measurable force, only microscopic forces occurring
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block and tackle[1] is a system of two or more pulleys with a rope or cable threaded between them, usually used to lift or pull heavy loads.
..... Click the link for more information.
Overview
Although used in many situations, they are especially common on boats and sailing ships, where motorized aids..... Click the link for more information.
In physics, power (symbol: P) is the rate at which work is performed or energy is transmitted, or the amount of energy required or expended for a given unit of time.
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torque (or often called a moment) can informally be thought of as "rotational force" or "angular force" which causes a change in rotational motion. This force is defined by linear force multiplied by a radius.
The SI unit for torque is the newton meter (N m). In U.S.
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The SI unit for torque is the newton meter (N m). In U.S.
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Speed is the rate of motion, or equivalently the rate of change in position, many times expressed as distance d traveled per unit of time t.
Speed is a scalar quantity with dimensions distance/time; the equivalent vector quantity to speed is known as
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Speed is a scalar quantity with dimensions distance/time; the equivalent vector quantity to speed is known as
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In physics and engineering, mechanical advantage (MA) is the factor by which a mechanism multiplies the force put into it. Following are simple machines where the mechanical advantage is calculated.
..... Click the link for more information.
- The beam shown is in static equilibrium around the fulcrum.
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Chain drive is a way of transmitting mechanical power from one place to another. It is often used to convey power to the wheels of a vehicle, particularly bicycles and motorcycles. It is also used in a wide variety of machines besides vehicles.
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hoist is a device used for lifting or lowering a load by means of a drum or lift-wheel around which rope or chain wraps. It may be manually operated, electrically or pneumatically driven and may use chain, fiber or wire rope as its lifting medium.
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split reel is a motion picture film reel in two halves that, when assembled, hold a specific length of motion picture film that has been wound on a plastic core. Using a split reel allows film to be shipped or handled in a lighter and smaller form than film would on a "fixed" reel.
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winch is a mechanical device that is used to wind up a rope or wire rope (also called "cable"). In its simplest form it consists of a spool and attached crank. The spool can also be called the winch drum.
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