Any mechanical or electrical device that transmits or modifies energy to performe some activity.
It make our work easier byIn a simple machine (máquina simple) a force is applied to the device at one point, and it does work moving a load, at another point. Although some machines only change the direction of the force.
- transferring a force from one place to another (a more convenient point),
- changing the direction (convert a rotary motion into a linear motion, up into down) of a force,
- increasing the magnitude of a force (lift weight much greater than one could do unaided),
- increasing the distance or speed (slow motion into a more rapid motion) of a force.
The mechanical advantage (ventaja mecánica) is the number of times a machine multiplies your effort force.
The actual mechanical advantage of a machine is always less than the theoretical value.
The efficiency (rendimiento o eficiencia) is the ratio between the amount of energy produced and the amount of energy expended and it is always less than 100 per cent.
The six classical simple machines:
- * Lever * Wheel and axle * Pulley
- * Inclined plane * Wedge * Screw and nut
Other mechanisms or elements of machines:A Compound or complex machine (máquina compuesta)
- * Winch or windlass
- * Friction wheels * Pulleys and belts
- * Sprockets and chain * Gears: Spur Gears, Bevel Gears, Worm Gear, Rack and Pinion
- * Eccentric wheel * Cam and follower. Camshaft
- * Crank and Connecting Rod. Crankshaft
- * Ratchet
- *Joints. Clutch. Universal joint or Cardan joint
- * Springs. Shock Absorber, shock, damper. Brakes
It is two or more simple machines working together to make work easier.
A device that changes electricity or fuel into movement and makes a machine work.
A machine that uses the energy from liquid fuel or steam to produce movement.
|Input force: Applied Force, Effort or Power|
Output force: Weight, Load or Resistance
Mechanical Advantage = Resistance force / Power force
Efficiency = Output energy / Input energy x 100
Work = Force · Distance
Torque (moment of a force) = Force x Distance.
A part of a machine, or a set of parts that work together.
Mechanisms are used to convert between one type of motion and another.
Motions are divided into six basic types:
- Linear motion, Uninterrupted objects will continue to move in a straight line indefinitely.
- Reciprocating motion is back and forth motion.
- Rotary motion is motion in a circle.
- Oscillation is back and forth motion about a pivot point.
- Intermittent motion is motion which starts and stops regularly.
- Irregular motion is motion which has no obvious pattern to its movement.
Mechanisms can be classified by function:
- Transmission of motion
- Linear transmission
- Block and tackle
- Rotary transmission
- Friction wheels
- Gear trains
- Pulley trains
- Transformation of motion
- Crank and rod
- Eccentric camCam
Energy accumulation / dissipation
Absorption or accumulation
- Shock absorbers
- Leaf springs
Transmission, control and support
- Rigid couplings
- Flexible couplings
- Plain bearing
- Antifriction bearings
A lever is a bar that is free to turn about a fixed point.
The mechanical advantage is the ratio of the resistance(load) arm to the power(effort) arm.
There are three different kinds (types) of levers:Wheel and Axle (rueda y eje)
- First Class Lever (palanca de primer género)
the fulcrum is located at some point between the effort and resistance forces.
It always changes the direction of force.
When the fulcrum is closer to the resistance, the output force is increased. However, there is a corresponding decrease in both output speed and distance.Examples : crowbars, scissors, pliers, pincers, tin snips and seesaws or teeter-totter, handle of water pump, a balance, a bicycle brake, mechanical balance ( a pair of scales), oars used in rowing, a claw hammer used for extracting nails, when you nod your head yes.
- Second Class Lever and Third Class Lever
the fulcrum is on the end, instead of in the middle.
- Second Class Lever (palanca de segundo género)
The resistance is located between the fulcrum and the effort force.
It does not change the direction of force.
The mechanical advantage is always greater than one.
Examples : nut crackers, wheelbarrows, bottle openers, the foot when it is used to lift the body
- Third Class Lever (palanca de tercer género)
The effort force is applied between the fulcrum and the resistance force.
The mechanical advantage is always less than one.
Examples : tweezers, a normal stapler, stapler remover, ice tongs, a fork used for eating, a shovel used for digging, fishing rod, a hammer driving a nail, a broom used for cleaning, a baseball bat, jockey bat, golf bat or racket when hitting the ball, the human forearm when it is used to lift an object..
A wheel and axle has a larger wheel (or wheels) connected by a smaller
cylinder (axle) and is fastened to the wheel so that they turn together.
The increased distance over which the force is applied as the wheel turns results in a more powerful force on the axle, which moves a shorter distance.
The mechanical advantage is the ratio of the radius of the wheel to the radius of the axle.
Examples: Door Knob, Wagon, Toy Car, Steering wheel, Screwdriver, Faucet (tap) handle and wrench (spanner), Bicycle handlebars, Hand crank.
Friction wheel(ruedas de fricción) or Friction drive
pulley and belt (polea y correa) or Belt drive
Two pulleys connected by a beltPulley (polea)
- They trasmit rotary motion
- change speed of rotation
- change torque -moment of a force-
- force and speed remain constant
- They slip easily
- To increase the speed of rotation and decrease the rotary force or torque: input:larger wheel, output:smaller wheel
- To increase the force of rotation or torque and decrease the speed of rotation: input:smaller wheel, output:larger wheel
- Spur gear and sprockets-chains are more reliable (you can trust)
- If D1,D2=diameter and N1,N2=angular velocity (speed in rpm) then D1xN1=D2xN2
- Gear Ratio (GR) is the relationship between the ouput diameter (D2) and input diameter (D1) - GR=D2/D1 -
- Speed Ratio (SR) is the relationship between the ouput speed (N2) and input speed (N1) - SR=N2/N1 or SR=1/GR -
- If GR is Gear Ratio and SR is Speed Ratio then N2=N1xSR
A wheel that usually has a groove around the outside edge. This groove is for a rope or belt to move around the pulley.Inclined plane (plano inclinado)
A sloping surface, such as a ramp. The mechanical advantage of an inclined plane is equal to the length of the slope divided by the height.
Examples: Staircase, Ramp, Bottom of a Bath Tub
It is used to split things. It can either be composed of one or two inclined planes. The mechanical advantage of a wedge can be found by dividing the length of the slope by the thickness of the big end.
There are two major differences between inclined planes and wedges. First, in use, an inclined plane remains stationary while the wedge moves. Second, the effort force is applied parallel to the slope of an inclined plane, while the effort force is applied to the vertical edge (height) of the wedge.
Examples: The cutting edge of scissors, Axe, chisel, Zipper, Knife.
Bolt or Screw (tornillo)
An inclined plane wrapped around a shaft or cylinder. It is a central core with a thread or groove wrapped around it to form a helix. While turning, a screw converts a rotary motion into a forward or backward motion, the distance moved is equal to the distance between two connective threads. This distance is called the pith.
It is used to hold things together. it may be used to raise weights or overcome resistance applied to its ends.
Archimedes Screw . An ancient device for lifting water. It consists of a spiral tube wrapped around an inclined rod. As long as the rod is turned, water enters through the open bottom end of the spiral and is slowly raised to the top where it pours out.
Examples: Bolt and nut, Spiral Staircase, screw press, screw jack.
Winch or Windlass (torno o cabrestante)
A machine which lifts or move heavy objects by turning a chain, cable, rope, belt or crank around a tube-shaped device (cylinder or barrel).
A windlass is an apparatus for moving a heavy weight. Typically, a windlass consists of a cylinder (barrel), which is rotated by the turn of a crank or belt. A winch is affixed to one or both ends, and a cable or rope is wound around the winch, pulling a weight attached to the opposite
It is really just a wheel with teeth. Two toothed wheels (driver and driven or follower) fit together either directly or through a chain or belt so one wheel will turn the other. Some gears may have a screw or a toothed shaft in place of one of the wheels. A gear may also be a combination of toothed wheels that produces a certain speed .
The gear ratio es the relationship between the number of teeth on two gears that are meshed or two sprockets conneted with a common roller chain or the circumferences of two pulleys connected with a drive belt.
In any pair of gears the larger one will rotate more slowly than the smaller one, but with greater rotation force (torque).
Examples: Clock, Automobile, Drill, bicycles, eggbeaters.
Eccentric wheel or eccentric cam (rueda excéntrica)
- Spur Gears (engranajes de dientes rectos)
They are the most common type of gears. They have straight teeth, and are mounted on parallel shafts. You won't find many in your car. They can be really loud (make a noise).
Examples: electric screwdriver, windup alarm clock, washing machine and clothes dryer.
- Bevel Gears (engranajes cónicos)
They are useful when the direction of a shaft's rotation needs to be changed. They are usually mounted on shafts that are 90 degrees apart, but can be designed to work at other angles as well.
- Helical Gears (engranajes helicoidales)
The teeth on helical gears are cut at an angle to the face of the gear. They operate much more smoothly and quietly than spur gears. For this reason, they are used in almost all car transmissions. They can be mounted on perpendicular shafts.
- Planetary Gearsets (engranaje planetario)
It has three main components: The sun gear, the planet gears and the planet gears' carrier and the ring gear.
Each of these three components can be the input, the output or can be held stationary. Choosing which piece plays which role determines the gear ratio for the gearset.
- Worm Gear (engranje de tornillo sin fin-corona)
It is a combination of a gear meshed with the threads of a screw. This combination changes the direction of turning motion by ninety degrees. Worm gears also decrease the speed of turning from screw to gear and increase its force. They are used when large gear reductions are needed. The worm can easily turn the gear, but the gear cannot turn the worm.
- Rack and Pinion (engranaje de piñon-cremallera)
A single gear, the pinion, meshes with a sliding toothed rack. This combination converts rotary motion (rotation) to back and forth motion (linear motion).
Examples: Windshield wipers in cars, the steering system on many cars.
- Sprocket and chain or Chain drive (rueda dentada y cadena)
- A wheel with teeth (sprocket) that engage with a chain
- To transmit powerful rotary movement
- Need to be lubricated
It is a disc with its centre of rotation positioned ‘off centre’. This means as the cam rotates the flat follower rises and falls at a constant rate.
Crank and Connecting Rod (biela-manivela)
A rotating disk shaped to convert circular (rotary motion) into reciprocating motion of the follower.
A ratchet is a device that allows a wheel to turn in only one direction. A bar on a pivot called the "pawl" is fixed above the ratchet wheel. The pawl slides over the teeth of the ratchet in one direction, but blocks the motion of the teeth if the wheel turns in the other direction.
Springs perform different actions.
Main types of spring:
Spring resisting stretching (extension spring). spring resisting compression (compression spring). spring that resists twisting (torsion spring).
A coupling that connects or disconnects driving and driven parts of a driving mechanism.
A pedal or lever that engages or disengages a rotating shaft and a driving mechanism.
A restraint used to slow or stop a vehicle.
Universal joint, U joint, Cardan joint (junta universal o Cardán)
It is a rigid rod that allows the rod to 'bend' in any direction, and is commonly used in shafts that transmit rotary motion. It consists of a pair of hinges located close together, oriented at 90° to each other, connected by a cross shaft.
shock absorber, shock, damper or dashpot (amortiguadores)
It is a mechanical device (one kind of dashpot) designed to smooth out or damp shock impulse, and dissipate kinetic energy.
Heat engines (máquinas térmicas)
Direct heat engine: They receive heat and convert part of it ot work.
External combustion engine (máquina de combustión externa)
The fuel was burnt outside of the engine in a boiler, to produce steam, which powered the engine.
Internal combustion engine (máquina de combustión interna)
- Steam engine (máquina de vapor)
Machine that uses steam power to perform mechanical work through the agency of heat.
- Double acting piston steam engine
It consists of a cylinder fitted with a piston . A connecting rod and crankshaft convert the piston's to-and-from motion into rotary motion. A flywheel tends to maintain a constant-output angular velocity in the presence of the cyclically changing steam pressure on the piston face. A slide valve admits high-pressure steam to the cylinder and allows the spent steam to escape .
The engine being powered by the expansion of hot gases produced by the burning of fuel
- Four stroke reciprocating internal combustion engine (motor de cuatro tiempos)
In combustion engines the inner energy set free by combustion ( e.g. of gasoline –petrol- or Diesel fuel ) is changed partly into mechanical energy.
The four strokes of the cycle are intake, compression, power or combustion, and exhaust. Each corresponds to one full stroke of the piston; therefore, the complete cycle requires two revolutions of the crankshaft to complete.
petrol engine (gasoline engine) (motor de gasolina)
The petrol(gasoline) engine uses a spark plug to ignite the air-fuel mixture.
The operation of the engine is divided into 4 parts, which are called strokes:
- 1st stroke (Intake) (admisión): The piston sucks in (the piston moves downward) the fuel-air-mixture from the carburetor into the cylinder. The intake valve is open and the exhaust valve is held shut by a spring.
- 2nd stroke (Compression) (compresión): The piston compresses the mixture (As the piston rises). The intake and exhaust valves are closed.
- 3rd stroke (Combustion or Power) (explosión): The spark from the spark plug inflames the mixture. The following explosion presses the piston to the bottom. The intake and exhaust valves are closed.
- 4th stroke (Exhaust) (escape): The piston presses the exhaust out of the cylinder. At the bottom of the power stroke, the exhaust valve is opened,
diesel engine (motor de gasoil o diesel)
The diesel engine uses the heat of compression to ignite the fuel.
The main differences are:
- 1st stroke (Intake): Only air is sucked in.
The intake valve opens, and fresh air (containing no fuel), is drawn into the cylinder.
- 2nd stroke (Compression): The air is powerfully compressed.
As the piston rises, the air is compressed, causing its temperature to rise. At the end of the compression stroke, the air is hot enough to ignite fuel.
- 3rd stroke (Combustion): Diesel is directly injected into the compressed air and ignites spontaneously.
Injection. Near the top of the compression stroke, the fuel injector drives fuel into the cylinder. The fuel immediately ignites upon contact with the hot compressed air.
Power. As the fuel burns, the gas in the cylinder heats and expands, driving the piston.
- 4th stroke (Exhaust):
The exhaust valve opens, and the exhaust is driven out of the cylinder.
- Gas turbine (turbina de gas)
Most of modern passenger and military aircraft are powered by gas turbine engines, which are also called jet engines.
Jet engines operate on the application of Newton's third law of motion: for every action there is an equal and opposite reaction.
In a gas turbine after air has been drawn into the engine through an inlet (intake), the air pressure is increased by a compressor before it enters the combustion chamber. The power required to drive the compressor is provided by a turbine that is placed between the combustion chamber and the nozzle.
- The turbojet engine (motor de reacción o turborreactor)
Turbojet engine derives its thrust by highly accelerating a mass of air , all of which goes through the engine. All of the propulsive force (100% of thrust ) produced by a jet engine derived from exhaust gas.
- After burning turbojet or turbofan (reactor de post-combustión)
The afterburner increases thrust by adding fuel to the exhaust gases after they have passed through the turbine section. Afterburning or " hot " operation or " reheating " is used only for a time limited operation of takeoff , climb , and maximum burst speed.
- The turbofan engine (reactor turboventilador)
Turbofan engine has a duct enclosed fan mounted at the front of the engine and driven either mechanically at the same speed as the compressor , or by an independent turbine located to the rear of the compressor drive turbine
The term "high-bypass" means that most of the air in the exhaust comes from the fan and flows past the rest of the engine, rather than flowing through it.
- The turboprop engine (reactor de turbohélice)
Turboprop engine derives its propulsion by the conversion of the majority of gas stream energy into mechanical power to drive the compressor , accessories , and the propeller load.
- The turboshaft engine (reactor de turboeje)
Turboshaft engine derives its propulsion by the conversion of the majority of gas stream energy into mechanical power to drive the compressor , accessories , The shaft on which the turbine is mounted drives the rotor of a helicopter through the reduction gearbox .
Reversed heat engine: They receive work and convert part of it to heat. Examples: refrigerator (fridge) and heat pump.