query: instance_of block 
supports: A rope is a group of yarns, plies, or strands that are twisted or braided together into a larger and stronger form. Ropes have tensile strength and so can be used for dragging and lifting, but are too flexible to provide compressive strength. As a result, they cannot be used for pushing or similar compressive applications. Rope is thicker and stronger than similarly constructed cord, line, string, and twine. Fiber rope is made from fiber, whereas wire rope is made from wire. On boats and ships, keel can refer to either of two parts: a structural element that sometimes resembles a fin and protrudes below a boat along the central line, or a hydrodynamic element. These parts overlap. As the laying down of the keel is the initial step in the construction of a ship, in British and American shipbuilding traditions the construction is dated from this event. Only the ship's launching is considered more significant in its creation. Sailing comprises wind propulsion of a craft by means of sails or other airfoils and steering it over water, ice or land, depending on the type of craft. A sailor manages the force of the wind on the sails by adjusting their angle with respect to the moving sailing craft and sometimes by adjusting the sail area. The force transmitted from the sails is resisted by forces from the hull, keel, and rudder of a sailing craft, by forces from skate runners for an iceboat, and by forces from wheels for a land sailing craft to allow steering a course on a point of sail with respect to the true wind. Wind is the flow of gases on a large scale. On the surface of the Earth, wind consists of the bulk movement of air. In outer space, solar wind is the movement of gases or charged particles from the Sun through space, while planetary wind is the outgassing of light chemical elements from a planet's atmosphere into space. Winds are commonly classified by their spatial scale, their speed, the types of forces that cause them, the regions in which they occur, and their effect. The strongest observed winds on a planet in the Solar System occur on Neptune and Saturn. Winds have various aspects, an important one being its velocity; another the density of the gas involved; another its energy content or wind energy. Wire rope is rope made from wire. It consists of several strands of metal wire laid (twisted) into a helix. The term "cable" is often used interchangeably with "wire rope", but narrower senses exist in which "wire rope" refers to diameter larger than 3/8 inch (9.52 mm), whereas sizes smaller than this are designated cable or cords. Initially wrought iron wires were used, but today steel is the main material used for wire ropes. A rudder is a primary control surface used to steer a ship, boat, submarine, hovercraft, aircraft, or other conveyance that moves through a fluid medium (generally air or water). On an aircraft the rudder is used primarily to counter adverse yaw and p-factor and is not the primary control used to turn the airplane. A rudder operates by redirecting the fluid past the hull (watercraft) or fuselage, thus imparting a turning or yawing motion to the craft. In basic form, a rudder is a flat plane or sheet of material attached with hinges to the craft's stern, tail, or after end. Often rudders are shaped so as to minimize hydrodynamic or aerodynamic drag. On simple watercraft, a tilleressentially, a stick or pole acting as a lever armmay be attached to the top of the rudder to allow it to be turned by a helmsman. In larger vessels, cables, pushrods, or hydraulics may be used to link rudders to steering wheels. In typical aircraft, the rudder is operated by pedals via mechanical linkages or hydraulics. A wheel is a circular component that is intended to rotate on an axle bearing. The wheel is one of the main components of the wheel and axle which is one of the six simple machines. Wheels, in conjunction with axles, allow heavy objects to be moved easily facilitating movement or transportation while supporting a load, or performing labor in machines. Wheels are also used for other purposes, such as a ship's wheel, steering wheel, potter's wheel and flywheel. Point of sail is a term used to describe a sailing boat's orientation in relation to the current wind direction. The circumference (from Latin "circumferentia", meaning "carrying around") of a closed curve or circular object is the linear distance around its edge. The circumference of a circle is of special importance in geometry and trigonometry. Informally "circumference" may also refer to the edge itself rather than to the length of the edge. Circumference is a special case of perimeter: the perimeter is the length around any closed figure, but conventionally "perimeter" is typically used in reference to a polygon while "circumference" typically refers to a continuously differentiable curve. An airfoil (in American English) or aerofoil (in British English) is the shape of a wing, blade (of a propeller, rotor, or turbine), or sail (as seen in cross-section). A sheave is a pulley with a grooved wheel for holding a belt, wire rope, or rope. The grooved wheel spins inside the frame of the sheave. This allows the wire or rope to move freely minimizing wear and abrasion on cable. Sheaves can be used to redirect a cable or rope, lift loads, and transmit power. The words "sheave" and "pulley" are sometimes used interchangeably. A pulley is a wheel on an axle or shaft that is designed to support movement and change of direction of a taut cable, rope or belt along its circumference. Pulleys are used in a variety of ways to lift loads, apply forces, and to transmit power. In nautical contexts, the assembly of wheel, axle, and supporting shell is referred to as a "block." A cable is two or more wires running side by side and bonded, twisted, or braided together to form a single assembly. The term originally referred to a nautical line of specific length where multiple ropes, each laid clockwise, are then laid together anti-clockwise and shackled to produce a strong thick line, resistant to water absorption, that was used to anchor large ships. In sailing , a block is a single or multiple pulley . One or a number of sheaves are enclosed in an assembly between cheeks or chocks . In use , a block is fixed to the end of a line , to a spar , or to a surface . A line ( rope ) is reeved through the sheaves , and maybe through one or more matching blocks at some far end , to make up a tackle . The purchase of a tackle refers to its mechanical advantage . In general the more sheaves in the blocks that make up a tackle , the higher its mechanical advantage . The matter is slightly complicated by the fact that every tackle has a working end where the final run of rope leaves the last sheave . More mechanical advantage can be obtained if this end is attached to the moving load rather than the fixed end of the tackle . There are various types of blocks that are used in sailing . Some blocks are used to increase mechanical advantage and others are used simply to change the direction of a line . A ratchet block turns freely when a line is pulled in one direction but does not turn the other direction , although the line may slip past the sheave . This kind of block makes a loaded line easier to hold by hand , and is sometimes used on smaller boats for lines like main and jib sheets that are frequently adjusted .
candidates: acting aircraft airplane angle assembly atmosphere bearing belt boat case change chemical circle component construction counter cross curve direction distance energy event fluid force gas group line object point polygon relation result running scale shape ship shipbuilding single six structural element surface term two variety wind wing wire
answer: case