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Transcript
Axle An axle is the central shaft for a rotating wheel or gear. An axle can either be in a fixed position, where a wheel or gear rotates around it, or it can be fixed to the rotating part. If the axle rotates with the wheel or gear it needs to be supported. An example of the latter is a bicycle wheel. Bearing A bearing is a device that separates fixed and moving parts. They are needed wherever rotating parts are found. To reduce friction and wear lubrication is needed. Belt Drive This is a continuous flexible belt that is usually used to transfer rotary motion from one pulley wheel to another. Numerous pulleys can be used together to create more complex systems. Examples of devices containing pulleys include: cassette recorders, video recorders and washing machines. Bevel Gear Bevel gears are conically shaped and are commonly meshed at right angles. This type of gear is only designed to work with other bevel gears and have to be precisely mounted. Block and Tackle Pulley This pulley system is a compound pulley system, using numerous pulleys per axle. This further increases its mechanical advantage. Bushing This is a fixing that separates two moving parts and/or strengthens a link between two parts. Cam A cam is a form of wheel which, depending on it shape and rate of rotation, affects the movement of a follower or rod which rests against it. A cam converts rotary motion into linear motion of the follower. Cams are found, for example, in car engines, sewing machines and toys. Chain A chain is a flexible connection made up of rigid, multiple parts. A chain can be used for numerous applications such as pulling, locking and holding parts together. Classes of Lever There are three classes of lever. Classes 1 and 2 are the most common types and they both provide a mechanical advantage (of 1 or more). Class 3 levers are less frequently used as they have a mechanical advantage which is less than 1. This means they need a greater force to move the load. Compound Pulley This type of pulley system uses both fixed and moveable pulleys. Crank Cranks convert rotary motion into reciprocating motion (and vice versa). A good example of this is the pedals of a bicycle turning the movement of the legs into the rotary motion of the wheel. Crankshaft A crankshaft is a shaft with integrated cranks. Rotational motion of the cranks causes rotational motion of the crankshaft. Crankshafts are commonly found in car engines, where the cranks are rotated by the reciprocating motion of the pistons. Crown Gear This is a special type of bevel gear that has its teeth at right angles to the plane of the wheel. It attaches to a spur gear, or pinion gear at right-angles. Driven Gear This is a name given to any gear that is not connected to a power source and is therefore driven by the driver gear. Driver Gear This is the name given to the gear that is connected to a power source and provides the movement to drive the other gears in the system. The power source is usually a motor. See Driven gear. Dynamo This was one of the first types of electrical generator, created in the early 19th century. A dynamo converts mechanical energy into electrical energy. Effort This is the name given to the force that is applied. Electric Motor An electric motor converts electrical energy into mechanical motion. The reverse task, converting mechanical motion into electrical energy, is performed by a generator or dynamo. Electricity Electricity is a property of matter that results from the presence or movement of electric charge. Equilibrium This is the name given to a state of balance, when both sides are equal. Fixed Pulley This type of pulley system has an axle that is fixed in place. It is used to redirect the rope/cable and has a mechanical advantage of 1. Force A force is an external cause responsible for any change of a physical system. Friction This is the term used to describe the force which resists the movement of one object when it is in contact with another. Fulcrum Is the name given to the point at which things rotate. Also known as a pivot. Gear A gear (or sprocket) is a toothed wheel that transfers rotary motion. Gears range is size from small plastic ones, used in small clocks, to large steel ones used in vehicle gearboxes. Different types of gear include the spur gear, bevel gear, rack-and-pinion gear, worm gear and the crown gear. Gear Ratio The gear (or velocity) ratio can relate to many types of mechanism. For example: 1. The comparison between the number of teeth of two meshed gears. 2. The comparison between the circumferences of two pulleys which are connected together by a belt drive. 3. The relationship between the movement of a lever and the movement of a load. To calculate the ratio for two meshed gears the number of teeth on the driven gear is divided by the number of teeth on the driver gear. Gear Train A gear train is a collection of two or more gears connected together to transmit rotary motion. Gearbox A gearbox consists of a gear train enclosed within a box. They are used, for example, in cars and sewing machines to obtain an increase or decrease in speed. Generator This is a device which produces electrical energy from a mechanical energy source. This process is known as electrical generation. Idler Gear An idler gear is a gear in a simple gear train that provides a change of direction of rotation but no change in speed of rotation between driver and driven gears. Inclined Planes An Inclined Plane is a plane that is set at an angle, other than a right angle, to a horizontal surface. It allows a high resistance to be overcome with a relatively small effort over a longer distance than the total height raised. Examples include: ramps, carpenter's planes, wedges and sloping roads. Input An input can be in many forms, for example a command, signal or force. Anything that is feed into a system is known as an input. For example, the weight pulling gears round inside a pendulum clock is providing an input. See also Process and Output. International System of Units (S.I. Units) This is the modern form of the metric system that uses internationally agreed units and definitions. For example, the S.I. unit for Force is the Newton. Lever A lever is created using a rigid object and an appropriate fulcrum (or pivot) to multiply the mechanical force on another object. The force applied to the lever is called the 'Effort' and the object being moved is called the 'Load'. Linear Motion Motion in a straight line. For example, a train's motion along a track. Linkage A linkage is the point where two parts join together. A linkage allows both movement to be transmitted as well as allowing changes in direction of movement. Load This is the name given to the object which is to be moved. Lubricant All material surfaces have irregularities, however small. If two surfaces move against each other friction and wear occur. Lubricant is a substance that is applied between touching surfaces to reduce friction. Typical examples of lubricants are oil and grease. Mechanical Advantage (MA) This is the amount by which a machine multiplies the effort put into it. For example; if you have a pulley system which requires 10lb. of effort to lift a 20lb. load the system has a mechanical advantage of 2. Moment The turning effect of a force when acting on an object that rotates around a pivot point. The moment can be calculated using the following formula: Moment = Force x Perpendicular distance from the pivot Motion Motion is the change in position of a body with respect to time. Different types of motion include; linear, oscillating, reciprocating and rotary motion. Motor A motor is a machine that converts some form of energy into mechanical energy. Various types of motors include, electric motors, pneumatic motors and hydraulic motors. Movable Pulley This type of pulley system has a 'free' axle meaning it can move in space. One end of the rope/cable is anchored meaning that by pulling the other end a doubled force will be applied to the load. This type of pulley has a mechanical advantage of 2. Newton The S.I. unit for force. Oscillating Motion Motion which moves repeatedly forwards and backwards in a circular direction. For example, the movement of a clock pendulum. Output A output is a name which can be given to any result of a process, within a system. For example, the rotary motion of the hands on a clock. See Input and Process. Pinion This is the name given to the smallest gear in a gear train. Piston A piston is a sliding plug that fits inside a cylinder. It is either used to exert pressure on a fluid in the cylinder or to change the volume inside it. Plane Theoretically this is surface with infinite height and width, zero thickness and zero curvature. Process This is the name given to any work, or task, that is done by a system. For example, the conversion of the reciprocating motion of a piston in a car engine to the rotary motion of the crankshaft is a process. Pulley A pulley is a wheel with a groove running along its edge which is used to hold a rope or cable. Pulleys can be used separately or in conjunction with each other to create systems which make lifting/moving loads easier. There are four types of pulley system; fixed, moveable, compound and block and tackle. Rack-and-Pinion Gear This type of gear converts rotary motion into linear motion, or vice versa. A circular gear, known as the pinion, engages with teeth on a toothed flat bar, known as the rack. As the pinion rotates the rack moves to the side in a linear direction. Reciprocating Motion Motion which moves repeatedly forwards and backwards (or 'to-and-fro'). For example, the motion of a piston within a car engine. Rotary Motion Motion in a circular direction. For example, the motion of a bicycle wheel. Screw A screw is a cylinder with a helical groove or thread running around its outside. They can be used to fasten things together, exert force, move loads or make accurate adjustments. Spool A cylinder for winding rope/thread/cable around. Spring Springs are used to store energy, apply force and to smooth out sharp joints. They can be made of naturally springy materials, such as rubber (elastic bands) or materials which need forming into special springs shapes (steel). Springs are used in numerous products, for example, vehicle suspension, measurement equipment and ball-point pens. Sprocket See Gear. Spur Gear This is the most common type of gear. Its teeth are positioned around its edge inline with the plane of the wheel. A Spur gear is also known as a 'Straight-Cut Gear'. Straight-Cut Gear See Spur Gear. Sub-system The name given to a specific part within a system, for example the 'Input'. Velocity Ratio The ratio of movement of one component compared to another in a mechanical syste. For example, the ratio of speed of rotation of gears in a gear train, or the ratio of distances moved by load and effort using a lever system. Wedge This is a simple machine that is used to separate two objects, or two parts of an object. <> Wheel A wheel is a circular object which, together with an axle, allows movement (rolling) with low friction. Winch A winch is a device used to wind up rope. In its simplest form it consists of a spool and an attached crank. Worm Gear This type of gear turns rotary motion through 90º and is used to either increase or decrease the rate of rotation. This type of gear is made up of a sprocket and a cylinder with a helical thread.