Unit D - Mechanical Systems - Section 1 - PDF

UNIT D: MECHANICAL SYSTEMS Engineering Design Process Activity Section 1 Machines are tools that help humans do work. 1.1 Simple Machines Meeting Human Needs Take a look at the following pictures. With a partner determine what they may have been used for. 6 Guess the machine! Guess the machine! This...

UNIT D: MECHANICAL SYSTEMS Engineering Design Process Activity Section 1 Machines are tools that help humans do work. 1.1 Simple Machines Meeting Human Needs Take a look at the following pictures. With a partner determine what they may have been used for. 6 Guess the machine! Guess the machine! This is a washing machine invented in 1870. It was intended to be much easier to use than a scrub board. Guess the machine! Guess the machine! This is a fence fabricating machine invented in 1888. Remarkably, modern chain-link fence-making machines don’t look much different. Guess the machine! Guess the machine! This is a brick-pressing machine invented in 1855, the earliest of three brick machines. Insert clay, add some elbow grease, and you’ve got a brick. Guess the machine! Guess the machine! This is a tobacco-cutting machine invented in 1878: a necessary step between tobacco fields and your cigarettes. Guess the machine! Guess the machine! This is a brush maker invented in 1877. An Irishman submitted this patent for an easier way to manufacture brooms and brushes. Roman Aqueducts Thousands of years ago, Roman engineers developed a mechanical system for transporting water for many kilometres to supply major cities. These structures, known as aqueducts, were made up of three main parts: 1. pumps to raise the water into reservoirs and control the rate of water flow 2. sloped channels to carry the water to the cities 3. distribution systems in the cities to carry the water to central bathhouses and local reservoirs. The aqueducts were so well designed and constructed that many of them can still be seen today in Europe, more than 2000 years after they were built! Sakia (Persian Wheel) Series of buckets attached to a long rope, draped over a wheel. Wheel is turned by animals which raises the buckets of water. After water is raised it is stored in tanks. Gravity moves water through pipes and into homes. Archimedes Screw His device used a large screw inside a tube. One end of the tube is placed in water. When the screw turns, it raises water up to the top of the tube. This device can move large volumes of water or other substances. Archimedes Screw STEM CHallenge Simple Machines 1. Levers First Class Second Class Third Class 2. Inclined Plane 3. Wedge 4. Screw 5. Pulley 6. Wheel & Axle Machine: A device that helps us to do work by transmitting or modifying energy. Simple Machines: Levers: People used levers to pry rocks out of the ground. Ramps: Then they used a ramp to help them raise the rocks as they built walls and other large structures. 1. Each machine was designed to meet specific needs, such as lifting rocks or splitting wood. 2. The first machines depended upon people of animals for their source of energy. Types of Simple Machines 1. 2. 3. 4. 5. 6. Levers Inclined Plane Wedge Screw Pulley Wheel & Axle 1. Levers First Class Second Class Third Class LEVERS A rigid bar or plank that can rotate around a fixed point called a pivot or fulcrum. Enables the user to move a larger load than without. But the user must move a greater distance than the load. TYPES of LEVERS First class lever – fulcrum between the load and the point of effort. TYPES of LEVERS Second class lever – load is between the effort and the fulcrum. TYPES of LEVERS Third class lever – has the effort between the load and the fulcrum. 2. Inclined Planes A flat surface that is at an angle to another flat surface, such as the ground. Enables the user to move a larger load than without. But the user must move a greater distance than the load. The ramp cannot be too steep in order to work. INCLINED PLANES A flat surface that is at an angle to another flat surface, such as the ground. Enables the user to move a larger load than without. But the user must move a greater distance than the load. The ramp cannot be too steep in order to work. 3. Wedges Similar to an inclined plane, but is forced into an object. By pressing on the wide end, the narrow end splits the object. Can only be used in one direction, to push objects apart. Enables the user to apply a greater force on an object. But the user must move a greater distance than the split. WEDGE Similar to an inclined plane, but is forced into an object. By pressing on the wide end, the narrow end splits the object. Can only be used in one direction, to push objects apart. Enables the user to apply a greater force on an object. But the user must move a greater distance than the split. 4. Screw Consists of a cylinder with a groove cut in a spiral on the outside. Can penetrate materials using a relatively small force. Converts rotational motion to linear motion. Most screws move objects very slowly. SCREW Consists of a cylinder with a groove cut in a spiral on the outside. Can penetrate materials using a relatively small force. Convert rotational motion to linear motion. Most screws move objects very slowly. 5. Pulley Made up of a wire, rope, or cable moving on a grooved wheel. May be made up of one or many wheels. Can be fixed in place or movable. Each time a pulley is added to the block and tackle mechanism the lifting force increases. As you increase the number of pulleys, - - the effort is less - distance you need to pull increases - object moves the same distance - effort to pull decreases resulting in a mechanical advantage PULLEY Made up of a wire, rope, or cable moving on a grooved wheel. May be made up of one or many wheels. Can be fixed in place or movable. Fixed pulleys are securely attached to an object. Movable pulleys are usually attached to the load. Fixed Movable Block & Tackle (pulley) A type of rope and pulley that uses blocks with many pulleys for even more lifting strength. Each time a pulley is added to the block and tackle mechanism the lifting force increases. Input Force x Number of pulley segments = Output Force 25N x 4 = 100 N Ex. The block and tackle image shows a load of 100N being lifted by pulling at 25 N. The total number of pulleys is 4. Each pulley segment adds a mechanical advantage of 1. The 4 pulley segments pulling add up to 100 N. 6. Wheel and Axle A machine made up of two wheels of different diameters the turn together. The larger wheel is considered the ‘wheel’ while the smaller wheel is considered the ‘axle’. When the simple machine turns around once, we call it one revolution. Force is usually linear it’s either a push or pull, however when force follows a circular motion it is called torque. During one revolution the larger wheel produces a longer motion, than the smaller axle which produces a shorter motion. WHEEL & AXLE A machine made up of two wheels of different diameters the turn together. The larger wheel is considered the ‘wheel’ while the smaller wheel is considered the ‘axle’. When the simple machine turns around once, we call it one revolution Force is usually linear it’s either a push or pull, however when force follows a circular motion it is called torque. During one revolution the larger wheel produces a longer motion, than the smaller axle which produces a shorter motion. 1.2 The Complex Machine A Mechanical Team 1.2 The Complex Machine: A Mechanical Team Complex Machine Development As larger communities developed, newer more complicated machines developed. New larger energy sources like coal, oil, and electricity combined with new technologies, caused an industrial revolution. This led to an increase in people’s standard of living. But has also led to people now being dependent on technology. Complex Machines: Development As larger communities developed, newer more complicated machines developed. New larger energy sources like coal, oil, and electricity combined with new technologies, caused an industrial revolution. This led to an increase in people’s standard of living. But has also led to people now being dependent on technology. Complex Machines COMPLEX MACHINES: A system in which there is an integration of simple machines all working together. SYSTEM: A group of parts that work together to perform a function. Ex. Bicycle (which simple machines does a bicycle employ) SUBSYSTEM: A smaller group of parts in a complex machine with one function. (Ex) Car - braking and steering Complex Machines COMPLEX MACHINES: A system in which simple machines all work together. SYSTEM: A group of parts that work together to perform a function. Ex. Bicycle (which simple machines does a bicycle employ) SUBSYSTEM: A smaller group of parts in a complex machine with one function. (Ex) Car - braking and steering Example: Bicycle Example: Pencil Sharpener Name some of the subsystems and their functions. Example: Pencil Sharpener Name some of the subsystems and their functions. Wedge to shape pencil Wheel Axle Subsystems Transfer Forces Linkage: A belt or chain to transfer energy from a energy source to an object. (Ex) bicycle chain Transmission: A special type of linkage for transferring energy from the engine to the wheel in large vehicles such as cars or trucks. Subsystems that Transfer Forces LINKAGE: A belt or chain to transfer energy from a energy source to an object. (Ex) bicycle chain TRANSMISSION: A special type of linkage for transferring energy from the engine to the wheel in large vehicles such as cars or trucks. - more useful when larger loads must be moved. - also known as a gearbox, or gear train Gears Gears: A pair of wheels with teeth that interlink; when they rotate together, one gearwheel transfers turning motion and force to the other. Four Characteristics of Gear 1. gear wheels work together in gear trains (2 or more gears) 2. gears can change the speed, force, and direction of motion 3. gears will alternate the direction of spin, if a driving gear spin clockwise the adjacent driven gear will spin counterclockwise 4. gears integrate with other gears , while gears that integrate with a linkage (ex. gears on a bike) are called sprockets Gear Directions When two gears are meshed together the driven gear will always turn in the opposite direction to the drive gear. To change the direction again another gear needs to be added to the gear train. CALCULATING COMPOUND GEARS GEARS: A pair of wheels with teeth that interlink; when they rotate together, one gearwheel transfers turning motion and force to the other. Characteristics of gears: 1. gear wheels work together in gear trains (2 or more gears) 2. gears can change the speed, force, and direction of motion 3. gears will alternate the direction of spin, if a driving gear spin clockwise the adjacent driven gear will spin counterclockwise 4. gears integrate with other gears , while gears that integrate with a linkage (ex. gears on a bike) are called sprockets MULTIPLYING GEARS: When driving gear is larger than the driven gear, the turning speed in the system increases. The larger driving gear will make one rotation while the smaller driven gear will make many rotations REDUCING GEARS: When driving gear is smaller than the driven gear, the turning speed in the system decreases. The smaller driving gear will make many rotation while the larger driven gear will make one rotation How do Gear Affect Speed? MULTIPLYING GEARS: When driving gear is larger than the driven gear = The turning speed in the system increases. The larger driving gear will make one rotation while the smaller driven gear will make many rotations REDUCING GEARS: When the driving gear is smaller than the driven gear = The turning speed in the system decreases. The smaller driving gear will make many rotation while the larger driven gear will make one rotation Section 1 QUIZ Section 2 Understanding Mechanical Advantage & Work SECTION 2 An understanding of mechanical advantage and work helps in determining the efficiency of machines. 2.1 Machines Make Work Easier 2.1 Machines Make Work Easier Mechanical Advantage The mechanical advantage of a machine is the amount by which a machine can multiply a force. The force applied to the machine is called the input force. The force the machine applies to the object is called the output force. MA = output force input force (load) (force you apply) or input arm distance output arm distance OF MA IA IF MA OA Calculating Mechanical Advantage (levers) MA = output force input force (load) (force you apply) or OF input arm distance output arm distance MA A force of 50N is applied to the end of a lever to lift a rock that is 350N. What is the MA of the lever? What is the output force (load)? 350N What is the input force? 50N What the MA? unknown Place all numbers into their correct location in the triangle. Cover the MA with your finger. Divide 350 by 50. Answer: 350N = 7. There is a mechanical advantage of 7. 50N OF MA IF 350 IF MA 50 Rules of MA 1. If MA = 0 there is no MA. 2. If MA > 0 you have MA, higher the MA the greater the advantage. This means you are using less force making it easier to move an object.. 3. If MA < 0 you have a situation where you are reducing the force required to move an object or when a machine is not working properly. IA MA = output force input force (load) (force you apply) or input arm distance output arm distance A lever is used to lift a heavy box weighing 500 newtons. The input arm of the lever is 0.5 meters long, while the output arm is 1.5 meters long. What is the mechanical advantage of the lever? What is the output arm length? 1.5M What is the input arm length? 0.5M What the MA? unknown Place all numbers into their correct location in the triangle. Cover the MA with your finger. Divide.5 by 1.5. Answer:.5 = 3. There is a mechanical advantage of 3. 1.5 MA OA IA MA OA 0.5 MA 1.5 Mechanical Advantage The mechanical advantage of a machine is the amount by which a machine can multiply a force. The force applied to the machine is called the input force. The force the machine applies to the object is called the output force. force you apply force the machine applies (load) In this example, the lever has exerted a force 5 x greater than the force you can exert without it. Practice MA = output force (load) input force (force you apply) or input arm distance output arm distance OF MA IF 1. IA MA OA Justin uses a wheelbarrow to move a load of bricks. The bricks weight 600 N, which is more than he could carry on his own. Justin uses the wheelbarrow to move the bricks. With the wheelbarrow he can move the bricks with only 120 N. What is the mechanical advantage? Practice MA = output force (load) input force (force you apply) or input arm distance output arm distance OF MA IF 1. IA MA OA Justin uses a wheelbarrow to move a load of bricks. The bricks weight 600 N, which is more than he could carry on his own. Justin uses the wheelbarrow to move the bricks. With the wheelbarrow he can move the bricks with only 120 N. What is the mechanical advantage? MA = Output Force Input Force MA = 600 N 120 N MA = 5, Justin can lift 5 x more with a wheelbarrow than without. INCLINED PLANE LAB Calculating Mechanical Advantage (pulleys) MA = MA = MA = MA = It is easy the calculate the MA of a pulley system by counting the number of pulleys within the system. No matter their diameter, the MA will always be the same as the number of pulleys. Calculating Mechanical Advantage (screws) MA - πdm l dm is the diameter of the screw head π is a constant at 3.14 l is the lead of the screw “pitch” (distance of one full rotation, distance between threads) 9mm Calculate the mechanical advantage of a screw whose radius is 9mm and pitch of 3mm. MA - πdm l MA - π (18) MA - π(18) = 14 4 4 A screw can have a much higher MA when a screwdriver or power tool is used. 4mm Calculating Mechanical Advantage (inclined planes) MA = length of slope height of the slope Calculate the mechanical advantage of a screw whose radius is 9mm and pitch of 3mm. MA = 3m 1m MA = 3 As the height increases and length remains constant, the MA decreases. As the height decreases and length remains constant, the MA increases. To increase the MA you need to increase length or decrease height. Calculating Mechanical Advantage (gears/gear trains) We can find the MA of gears and the GEAR RATIO (GR). MA = 30 = 0.5 60 or GR = 30 = 3 = 3 / 3 = 1 60 6 6 / 3 = 2 GR = 1:2 For every one turn of the driver, the driven turns two times. Calculating Mechanical Advantage (gears/gear trains) Calculate the MA and GR of the following. Number of teeth of driven gear Number of teeth of driver gear When two gears are meshed a mechanical advantage is produced if the circumference of the gears differs MA = 30 teeth 20 teeth MA = 1.5 The more a machine multiplies force, the greater its mechanical advantage. This allows you to lift a much heavier load than without the pulley In using the pulley, you have to pull much farther than the load actually moves. If MA is greater > 1 - less input force is required to overcome the output force - greater input distance is required to overcome the output force If MA is less < 1 - greater input force is required to overcome the output force. - less input distance is required to overcome the output force. MA cannot equal zero. MECHANICAL ADVANTAGE of OTHER SIMPLE MACHINES Which of the above ramps would have a greater Mechanical Advantage (MA)? Speed Ratio Speed measures the distance an object travels in a given amount of time. The measure of how the speed of the object is affected by a machine is called the speed ratio. An inclined plane makes it possible to lift heavy objects using a smaller force (examples: loading ramp, wheelchair access ramp), but you have to move the object over a much longer distance. Speed measures the distance an object travels in a given amount of time. A measure of how the speed of the object is affected by a machine is called the speed ratio. Effort force is the input force. Describes how much faster the user is moving than the load is moving. Output Number of Teeth Input Number of Teeth MA = 30 teeth SR = 30 teeth 20 teeth 20 teeth MA = 1.5 SR = 3:2 Number of teeth of driven gear Number of teeth of driver gear Calculate the Mechanical Advantage (MA) and Speed Ratio (SR) of each of the following: Calculate the Mechanical Advantage (MA) and Speed Ratio (SR) of each of the following: Describes how much faster the user is moving than the load is moving. MA = 10 / 5.2 = 1.9 SR = 1 /.5 = 0.5 MA = 20 / 7 = 2.9 SR = 30/ 10 = 3.0 The Effects of Friction on MA Friction can have a significant impact on mechanical advantage. Frictional forces will reduce the efficiency of a machine and result in a decrease in the mechanical advantage of the machine. The machine will require more force to operate, which could make it difficult or impractical to use. One way to reduce the effects of friction on mechanical advantage is to lubricate the machine's moving parts so that they can move more easily. An example of this effect is seen in pulley systems. While ideal pulleys, with no energy loss due to friction, would have a constant mechanical advantage at every pulley, real-world pulleys experience energy loss due to friction. Efficiency EFFICIENCY: Measurement of how well a machine or device uses energy. Efficiency of a system is negatively affected by friction. Most energy is lost and unusable (Ex. Lost as heat) Most complex machines are very inefficient: waste energy. Ex. A car is only 15% efficient, where does the rest of the energy go? Example: An appliance with an output of 8100J of useful energy is supplied with 9000J. What is its efficiency? E = useful output energy = 8100J x 100 total input energy 9000J E = 90% Example: An appliance with an efficiency of 25% is supplied with 9000J. What is its useful output energy?.25 = useful output energy 9000.25 x 9000 = useful output energy 2250J Example: An appliance with an efficiency of 90% is supplied with 9000J. What is its useful output energy?.90 = useful output energy 9000.90 x 9000 = useful output energy 8100J Efficiency EFFICIENCY: Measurement of how well a machine or device uses energy. Efficiency of a system is negatively affected by friction. Most energy is lost and unusable (Ex. Lost as heat) Most complex machines are very inefficient: waste energy. Ex. A car is only 15% efficient, where does the rest of the energy go? Useful Output Energy Total Input Energy EFFECT of FRICTION Friction can be an important factor in a mechanical system because it opposes motion. This means that extra force is needed to overcome friction whenever you move an object. The mechanical advantage of a device is affected by friction but the speed ratio is not. Friction is caused by the roughness of materials. Friction can also cause heat which is an additional concern. Efficiency Example: An appliance with an efficiency of 25% is supplied with 9000J. Useful Output Energy What is its useful output energy? Total Input Energy Efficiency Useful Output Energy Total Input Energy Example: An appliance with an efficiency of 25% is supplied with 9000J. Example: An appliance with an efficiency of 90% is supplied with 9000J. What is its useful output energy? What is its useful output energy?.25 = useful output energy 9000.90 = useful output energy 9000.25 x 9000 = useful output energy.90 x 9000 = useful output energy 2250J 8100J 2.2 The Science of Work The Meaning of Work Work is done when a force acts on an object to make the object move. If there is no force on an object, then no work is being done. Amy uses 20N of force to push a lawn mower 10 meters. How much work does she do? W = F.d W = 20N. 10 meters W = 200 Joules The work input is the work done by the student using the machine—the inclined plane—to lift the person in the wheelchair. In this case, the pushing student exerts a force of 320 N for a distance of 5 m. You can use the formula for work to calculate the work input: 320N x 5 m = 1600 J Without the inclined plane, the force needed to lift the straight up would be 800N over the 2 meters: 800n x 2 m = 1600 J 5m 2m As a result the same work is done no matter regardless of mechanical advantage. The Meaning of Work Work is done when a force acts on an object to make the object move. Calculating Work Calculating Work Amy uses 20N of force to push a lawn mower 10 meters. How much work does she do? W = F.d W = 20N. 10 meters W = 200 Joules If you use a machine so you do not have to exert as much force, you still perform the same amount of work. Calculating Work If you use a machine so you do not have to exert as much force, you still perform the same amount of work. The work input is the work done by the student using the machine—the inclined plane—to lift the student in the wheelchair. In this case, the pushing student exerts a force of 320 N for a distance of 5 m. You can use the formula for work to calculate the work input: 320N x 5 m = 1600 J 5m 2m Without the inclined plane, the force needed to lift the student straight up would be 800N over the 2 meters: 800n x 2 m = 1600 J Friction is also the reason that work input does not equal work output in real situations. It affects a machine’s efficiency 2.3 Hydraulics Pressure in Fluids Pressure is a measure of the amount of force applied to a given area. A hydraulic system uses a liquid under pressure to move loads. A hydraulic system increases the mechanical advantage of the levers in machines. A pneumatic system uses a air under pressure to move loads. A hydraulic system increases the mechanical advantage of the levers in machines. Calculating Pressure Pressure is a measure of the amount of force applied to a given area. The smaller the area, the greater the pressure. Force unit = Newtons (N) Pressure unit = Pa (Pascals) Area unit = m2 Calculate the pressure on a man’s foot when a woman who weighs 520 N steps on his foot with her heel which has an area of 0.001 m2 with all of her weight. P=F A P = 520 J.001 m2 P = 520 000 Pa (Pascals) Pressure in Fluids A hydraulic system uses a liquid under pressure to move loads. A hydraulic system increases the mechanical advantage of the levers in machines. A pneumatic system uses a air under pressure to move loads. A hydraulic system increases the mechanical advantage of the levers in machines. Pressure in Fluids Pressure is a measure of the amount of force applied to a given area. Pascal’s Law (pressure) States “that an enclosed fluid transmits pressure equally in all directions. Hydraulic Advantage Hydraulics creates a mechanical advantage as a result of Pascal’s Law on pressure. The MA is force multiplied throughout the system. What is the total force exerted on P2? 15 = 1000 60 x 15x = 60(1000) 15x = 60,000 15 15 Area of P1 = 15 cm3. Total force of P1 = 1000 N Area of P2 = 60 cm3 x = 4000 N 4000 / 1000 = 4 The MA of the system is 4. The force is multiplied 4 x. Hydraulic Advantage In the hydraulic jacks below, the input piston remains the same. The output piston size is increased allowing for a greater multiplication of force. As the output piston size increases so does the ability to lift heavier objects. Pascal’s Law States “that an enclosed fluid transmits pressure equally in all directions. Hydraulic Advantage 100 lb of input force causes 900 lbs of output force (100 lbs x 9 inches = 900) A smaller force on one piston can create a much large force on the other. Mechanical Advantage of a Hydraulic System The output force is 25 x more than the input force. The force is multiplied. Section 2 QUIZ Section 3 Development & Evaluation of Mechanical Devices 3.1 Evaluating Mechanical Devices Mechanical devices are constantly being evaluated. Manufacturers evaluate the devices they make to find ways to improve them. Machines and mechanical devices have evolved over time because of science and the development of new technologies. Bicycles have evolved in both design and function as new technologies were discovered. A bicycles main function is movement/travel. However, new materials have allowed bicycles to be used for racing, stunts and mountain biking. Mountain Bikes Road bikes are designed for all sorts of paved-surface riding. These bikes are lightweight and aerodynamic, designed to be fast in a straight line but also fast uphill. Their frame geometry, components, and handlebar shape lend them to being fast. Road Bikes Mountain bikes are designed for off-road riding. The thick tires and treads on mountain bikes make them extremely slow on tarmac, as if the heavy frame wasn’t slowing you down enough, though they're perfectly suited to helping you stay upright on rocky, muddy singletrack trails. The flat handlebars and suspension systems on mountain bikes are meant to increase handling and improve comfort off-road, and especially on steep and technical singletrack. A mountain bike’s frame geometry is designed to help cushion blows and improve balance. They have a large gear range and disc brakes. 1930s Church Key 1950s Ermal Fraze developed the pull tab to open cans when he needed to use his bumper to open cans at a picnic. These tabs became a concern when they were heavily discarded everywhere. To avoid loose tabs, the pop top can was invented. However, when pushing on the openings you could cut your finger. In 1975 Daniel Cudzik created the pop top can. At first the mouth was not large enough but was widened to avoid the glug,glug sound it emitted. The full aperture is the most recent creation, however, not in wide use. Technological Advances Technology and devices have come a long way since the invention of simple machines. Advances in technology can have broad implications on human society: Changes in society (ex. robots) Changes in the environment (biodegradable plastic to to help our environment) Changes in production capacity (new tech has resulted in the speed of production) Changes in human behaviour (Covid led to the advancement of technology for remote working) Evaluating Better Designs Q: So how do people (engineers/designers) know which mechanical device is the best? A: They use a set of criteria to evaluate and analyze the mechanical device. (we need a system to keep score!) DESIGN EFFECTIVENESS Is there a better design to complete its function? Does it fulfill its function well without breaking for prolonged periods? (ex. gas powered mower vs. push mower) UNWANTED COSTS COSTS Does it create wastes? (ex. Gas powered lawn mower has more parts than a push mower) Is it expensive to build? Is it easy to manufacture, can it be manufactured quickly? EFFICIENCY Does it perform work efficiently? (ex. using a push mower takes longer to mow the lawn) AESTHETICS Does it look pleasing to the eye, does it need to look pleasing? Perhaps the device works great only in certain environments? ENVIRONMENT (ex. BMX bike for Tour de France) Is it being used safely? (ex. single speed bike in a BMX course) Does it negatively impact the environment? ERGONOMICS How well do humans interact with the device? EValuation of Machines Project Unit D FINAL EXAM