Pre-Class Friday 9+2=11 What do you think a Mechanical Engineer does?

Mechanical Engineering One of the largest and broadest engineering fields, second only to Electrical in number of engineers employed

What is it? Involved in the design, development, production, control, operation, and service of machines and mechanical devices Involved in the design, development, production, control, operation, and service of machines and mechanical devices One of the largest and broadest engineering disciplines One of the largest and broadest engineering disciplines Starting salary 2009: $58,766 with the average salary in 2005: $50,175 Starting salary 2009: $58,766 with the average salary in 2005: $50,175 Two main divisions: Two main divisions: –Design and controls = involves the detailed layout and assembly of the components of machines and mechanical devices –Thermal sciences = study of the flow of fluids and the flow of energy between systems

Design and Controls Most common function of mechanical engineering Most common function of mechanical engineering Ensure parts fit together by specifying detailed dimensions Ensure parts fit together by specifying detailed dimensions Develop computational models to aid design engineers Develop computational models to aid design engineers How to control the device can involve mechanical or hydraulic, with modern systems incorporating a digital interface How to control the device can involve mechanical or hydraulic, with modern systems incorporating a digital interface Acoustics (study of sound) is important by the noise generated by the design or control systems Acoustics (study of sound) is important by the noise generated by the design or control systems

Thermal Sciences Fluids can be liquids, gases, and two-phase flows (combination of liquids and non- liquids) Fluids can be liquids, gases, and two-phase flows (combination of liquids and non- liquids) Heat transfer is the flow of energy due to a temperature difference Heat transfer is the flow of energy due to a temperature difference Used in the design and development of engines Used in the design and development of engines –Internal combustion : cars –Gas turbine : airplanes

Pre-Class Tuesday Write: “Guest speaker: Zine Smith, Systems Engineering.”

WHAT IS A MACHINE? A machine is a device that makes “work” easier. A machine is a device that makes “work” easier. A simple machine makes “work” easier, but only has one moving part. A simple machine makes “work” easier, but only has one moving part.

SIMPLE MACHINES Lever Wedge Inclined plane Pulley Wheel and axle Screw

Gear Ratio Gears are wheels with teeth designed to make work easier Gears are wheels with teeth designed to make work easier The gear ratio quantitatively describes the effectiveness of a series of gears The gear ratio quantitatively describes the effectiveness of a series of gears Gear ratio = N p /N s = v s /v p = d p /d s, where Gear ratio = N p /N s = v s /v p = d p /d s, where –N s : the number of teeth for the secondary gear –N p : the number of teeth for the primary gear –v s : the speed of the secondary gear –v p : the speed of the primary gear –d s : the diameter of the secondary gear –d p : the diameter of the primary gear Side note: two touching gears will always turn in opposite directions Side note: two touching gears will always turn in opposite directions

You have to find the odd ones out in the groups of words, but there's a catch. Each group of words has TWO words which do not belong. Can you find them both? King - Earl - Knight - Bishop Not a chess piece Not a class of nobility Pre-Class Wednesday

Gear Ratio Practice Two gears are attached as shown. Two gears are attached as shown. If the gray gear spins clockwise, then the orange gear spins _____. If the gray gear spins clockwise, then the orange gear spins _____. If the orange gear is the primary, what is the gear ratio? If the orange gear is the primary, what is the gear ratio? CCW 2/3 or 0.67

More Gear Ratios The primary gear is spinning at 9 revolutions per second (rev/s). The primary gear is spinning at 9 revolutions per second (rev/s). The gear ratio is 4/3. The gear ratio is 4/3. Find the speed of the secondary gear. Find the speed of the secondary gear. 12 revolutions per second or 12 rev/s

Using the Geared Up Lab 1. On your lab, add a new column to the right called “Gear Ratio.” 2. Find the Gear Ratio using the number of teeth and the equation. 3. Measure the diameter of each gear and include that with the “size.” 4. Solve for the Gear Ratio and compare with the one in #2. Which is more accurate?

Gearing Down (Up?) Lab Objective Objective –To vary the gear ratio of a vehicle to adjust its speed Materials Materials –Lego Mindstorm kit (2 motors max) –Stopwatch –Meter stick –Calculator Procedures Procedures –Build a vehicle that can driven by an electric motor. –Be flexible in the design to adjust the number of gears used. –The size of the tires cannot change and the weight of the vehicle must remain relatively constant. –Attach the RCX, turn it on, and measure the time needed for your vehicle to travel 3 meters

Gearing Down (Up?) ScenarioTrial # of gears Gear ratio Speed (m/s) Average Above Below 1 2 3

Pre-Class Thursday Two gears are attached on different shafts but are close enough together that if one spins, so does the other. If gear 1 has 16 teeth and gear 2 has 48 teeth, how many revolutions will gear one have to spin through for gear 2 to make one revolution?

Pre-class Friday

Another area & Divisions Combination of both with heating, ventilating, and air conditioning (HVAC) Combination of both with heating, ventilating, and air conditioning (HVAC) Some divisions (p75, 76): Some divisions (p75, 76): –Aerospace –Bioengineering –Dynamic Systems and Control –Fluids –Manufacturing –Nuclear –Pressure Vessels and Piping –Safety and Risk Analysis –Textile

Pre-Class Monday True or false: A gear is considered one of the six simple machines.

Pre-Class Tuesday After the recent snail racing contest, the four contestants were congratulating each other. Only one snail wore the same number as the position it finished in. Alfred's snail wasn't painted yellow nor blue, and the snail who wore 3, which was painted red, beat the snail who came in third. Arthur's snail beat Anne's snail, whereas Alice's snail beat the snail who wore 1. The snail painted green, Alice's, came second and the snail painted blue wore number 4. Anne's snail wore number 1. Can you work out who's snail finished where, its number and the color it was painted? # Owner Wore Color 1 Alfred 3 red 2 Alice 2 green 3 Arthur 4 blue 4 Anne 1 yellow

Pre-Class Monday Write: “Review for written and prepare for performance test.”

Pre-Class Wednesday What is your favorite event of the Winter Olympics?

Pre-Class Thursday Write: “Guest speaker: John Allen from Southern Construction and Design.”

Pre-Class Wednesday Pirate Pete had been captured by a Spanish general and sentenced to death by his 50-man firing squad. Pete cringed, as he knew their reputation for being the worst firing squad in the Spanish military. They were such bad shots that they would often all miss their targets and simply maim their victims, leaving them to bleed to death, as the general's tradition was to only allow one shot per man to save on ammunition. The thought of a slow painful death made Pete beg for mercy. "Very well, I have some compassion. You may choose where the men stand when they shoot you and I will add 50 extra men to the squad to ensure someone will at least hit you. Perhaps if they stand closer they will kill you quicker, if you're lucky," snickered the general. "Oh, and just so you don't get any funny ideas, they can't stand more than 20 ft away, they must be facing you, and you must remain tied to the post in the middle of the yard. And to show I'm not totally heartless, if you aren't dead by sundown I'll release you so you can die peacefully outside the compound. I must go now but will return tomorrow and see to it that you are buried in a nice spot, though with 100 men, I doubt there will be much left of you to bury." After giving his instructions the general left. Upon his return the next day, he found that Pete had been set free alive and well. "How could this be?" demanded the general. "It was where Pete had us stand," explained the captain of the squad. Where did Pete tell them to stand?