THE BUSINESS 101 MAGAZINE PRESENT POETIC MOMENTS WITH DAWN PULIDO
ME 101: Forces & Moments (Continued) Chapter 4 ME-101 1.
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Transcript of ME 101: Forces & Moments (Continued) Chapter 4 ME-101 1.
ME 101:
Forces & Moments(Continued)
Chapter 4
ME-1011
Particle/Rigid Body
• Particle – A very small amount of matter assumed to
occupy a single point in space
• Rigid Body – A combination of a large number of
particles that are fixed relative to one another
ME-1012
Newton’s 3 Fundamental Laws
• First Law – If the resultant force acting on a particle
is zero, the particle will remain at rest (if originally at
rest) or will move with constant speed in a straight
line (if originally in motion)
• Second Law:
• Third Law – The forces of action and reaction
between bodies in contact have the same magnitude,
same line of action, and opposite sense
ME-101
amF
3
Equilibrium
ME-101
0 FR
0 FrMM
1F
2F 3F
3r
2r
1r
4
Equilibrium (in 2-D)
ME-101
0xF
0yF
0oM
Particle is in
equilibrium if forces balance (zero
resultant)
Rigid body is in
equilibrium if forces and
moments balance
5
Free Body Diagram (FBD)
Forces and moments acting on a body are applied to a
simplified version of the body
ME-101
W
Fchair
W
Fchair
6
How to Draw a FBD
1. Isolate the body from its surroundings and draw a simplified version of it
2. Use an appropriate coordinate system (Usually Cartesian) and include it with your FBD
3. Add the loads to the body in appropriate locations with proper direction and magnitude
4. Label all known quantities
ME-1017
T
Example
ME-101
WB
TWA
NA
A
B
Fapp
Pulley
θ
Assume surface is smooth – no friction
What is FBD of Block A? Block B?
Fapp
Use the free body diagram to evaluate the system
y
x
θ 3
4
5
8
Example
The mass center G of the 1400 kg rear engine car is
located as shown in the figure
Determine the normal force under each tire when the
car is in equilibrium
ME-1019
Example
ME-10110
Example
• Determine the pull P on the rope
exerted by the man to hold the
crate in the position shown
• Also find the tension T in the
upper rope
ME-10111
Example
Compute the moment about point O
ME-10112
Design Applications
ME-10115
Hyatt Regency Hotel in Kansas City
• July 17, 1981
• Killing 114
• Injuring 200+
• Worst structural disaster in U.S. history
• The engineering firm that approved the final
plans was stripped of its license
• http://www.onlineethics.org/CMS/
profpractice/ppcases/texindex/
hyatt_walkway.aspx
ME-10116
Why?
ME-10117
The initial plan and final deviation
ME-101
http://azurebrooke.com/
18
Beam Failure
ME-10119
Design Application: Bearings
Two types of bearings
– Rolling-Element • Balls or rollers between inner and outer race
• Very common
– Journal• Shaft in lubricated sleeve
• Rotates on film of oil
• Examples – Engine crankshafts, pumps, and compressors
ME-10120
Radial Ball Bearing
ME-10121
Ball and Roller Contact Stress
ME-101
Max shear stress occurs below the surface, failure appears as cracks, pits, or flakes
22
Roller Bearings
Higher Loads – Axial or Radial
ME-10123
How to Size Component
• Create FBD
• Determine loads acting on component
• Determine size of component– Consider Non-Traditional Solutions
– Factor of Safety
– Consider Dimensional Constraints
– Cost
– Manufacturability
– Ease of Assembly
ME-10124
Bearing Selection
ME-10125