Pre-Class Friday 9 2=11

1
Pre-Class Friday 9211

• What do you think a Mechanical Engineer does?

2
Mechanical Engineering

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

3
What is it?

• Involved in the design, development, production,
  control, operation, and service of machines and
  mechanical devices
• One of the largest and broadest engineering
  disciplines
• Starting salary 2009 58,766 with the average
  salary in 2005 50,175
• 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

4
Design and Controls

• Most common function of mechanical engineering
• Ensure parts fit together by specifying detailed
  dimensions
• Develop computational models to aid design
  engineers
• 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

5
Thermal Sciences

• 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
• Used in the design and development of engines
• Internal combustion cars
• Gas turbine airplanes

6
Pre-Class Tuesday 9-6-11

• Write Guest speaker Zine Smith, Systems
  Engineering.

7
WHAT IS A MACHINE?

• A machine is a device that makes work easier.

• A simple machine makes work easier, but only
  has one moving part.

8
SIMPLE MACHINES

• Lever
• Wedge
• Inclined plane
• Pulley
• Wheel and axle
• Screw

9
Gear Ratio

• Gears are wheels with teeth designed to make work
  easier
• The gear ratio quantitatively describes the
  effectiveness of a series of gears
• Gear ratio Np/Ns vs/vp dp/ds, where
• Ns the number of teeth for the secondary gear
• Np the number of teeth for the primary gear
• vs the speed of the secondary gear
• vp the speed of the primary gear
• ds the diameter of the secondary gear
• dp the diameter of the primary gear
• Side note two touching gears will always turn in
  opposite directions

10
Pre-Class Wednesday 9-7-11

• 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

11
Gear Ratio Practice

• Two gears are attached as shown.
• If the gray gear spins clockwise, then the orange
  gear spins _____.
• If the orange gear is the primary, what is the
  gear ratio?

CCW
2/3 or 0.67
12
More Gear Ratios

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

12 revolutions per second or 12 rev/s
13
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?

14
Gearing Down (Up?) Lab

• Objective
• To vary the gear ratio of a vehicle to adjust its
  speed
• Materials
• Lego Mindstorm kit (2 motors max)
• Stopwatch
• Meter stick
• Calculator
• 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

15
Gearing Down (Up?)
Scenario Trial of gears Gear ratio Speed (m/s)
Average 1
Average 2
Average 3
Above 1
Above 2
Above 3
Below 1
Below 2
Below 3
16
Pre-Class Thursday 9-8-11

• 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?

3
17
Pre-class Friday 9-9-11
18
Another area Divisions

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

19
Pre-Class Monday 9-12-11

• True or false
• A gear is considered one of the six simple
  machines.

20
Pre-Class Tuesday9-13-11

• 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  Color1 Alfred  3  
   red2  Alice    2      green3  Arthur  
4      blue4  Anne     1      yellow
21
Pre-Class Monday 2-21-11

• Write Review for written and prepare for
  performance test.

22
Pre-Class Wednesday 2-17-10

• What is your favorite event of the Winter
  Olympics?

23
Pre-Class Thursday 09-17-09

• Write Guest speaker John Allen from Southern
  Construction and Design.

24
Pre-Class Wednesday 9-16-09

• 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?