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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.
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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.