POE EOC Review
Terms in this set (92)
Ideal Mechanical Advantage = Distance effort moves / distance load moves
Actual Mechanical Advantage = Load / Effort
= AMA / IMA x 100%
Nothing in the real world is more than 100% efficient.
Classification of Levels:
• Class 1 fulcrum is in the middle
• Class 2 load is in the middle
• Class 3 effort is in the middle
IMA of a lever
Length of effort arm/ length of load arm
IMA of a wheel and axel
radius of effort arm/ radius of load arm
IMA of a screw
circumference / pitch of screw (inches per thread)
IMA of a inclined plane
Length of sloped side of the ramp/ height of ramp
IMA of a wedge
Length of sloped side of the wedge/ width of the wedge
IMA of a pulley
Number of strands supporting the load
MAtotal = MA1 X MA2 X MA3 X...
rotational speed (rpm)
torque (in lbs or Nm)
Gear Ration (GR)
Number of teethout / number of teethin. = No/Ni
No/Ni = Do/Di = τo / τi = ωi / ωo
Sprockets use chains
noisier, more expensive, stronger, need lubrication
Driver pulleys use belts
quieter, cheaper, weaker, no lubrication
can be used up
EX: oil, coal, uranium.
more can be made
EX: bio fuels, plants, animals
we don't do anything to make more
EX: solar, wind, hydro-electric
Force x Distance
• Hydrogen fuel cells combine hydrogen and oxygen to
• They create no pollution, only water.
• It is an emerging technology with many issues such as
storage and distribution.
Matter is made up of molecules in motion (kinetic energy)
occurs when all kinetic energy is removed from a object 0 K = -273° C
1st law of thermodynamics
Energy cannot be created or destroyed.
2nd law of thermodynamics
thermal energy moves from hot to cold -
Entropy (measure of disorder of energy) always increases.
3rd law of thermodynamics
the entropy of a system at absolute zero is a well-defined constant.
Thermal energy can be transferred
convection (moving fluid), conduction (touching objects)
or radiation (electromagnetic waves through space or air).
Rate of transfer
ΔT/r-value = k
*A *ΔT / L
r-value= thermal resistance
A = area
k = thermal conductivity.
Heat Energy transfer
Cp= specific heat capacity of a material
m= mass of the object
Multiple Layers of Insulation
Add the r-values of multiple layers to get the total r-value
Newton's First Law of Motion (law of inertia)
An object in a state of rest or uniform motion
will continue to be so unless acted upon by another force.
Newton's Second Law of Motion
The acceleration of an object is proportional to the net force acting on the object and inversely proportional to the object's mass. (F=MA)
Newton's Third Law of Motion
For every action force, there is an equal and opposite reaction force
A condition where there are no net external forces acting upon a particle or rigid body and the body remains at rest or continues at a constant velocity.
Σ Moments = 0, Σ Forces in x direction = 0, and Σ Forces in y direction = 0
the rotational forces acting on an object = Force * perpendicular distance.
the center of mass of an object and can be calculated from its dimensions.
• Square: x = xmax/2; y = ymax/2
• Square: x = xmax/3; y = ymax/3
• Square: x = radius; y = (4 x radius) / (3 x π)
Centroid of compound shapes
x = Σ (xi * Ai) / Σ xi ,
xi= centroid of each shape
Ai= area of each shape.
Moment of Inertia
describes the stiffness of a beam due to its cross section
I = bh3/12 for a rectangular cross section with height of h and width of b
describes how much it can bend = FL3 / (48 E I)
I= moment of inertia
E= the modulus of elasticity, a property of the material.
Free Body Diagrams
illustrate forces acting upon a given body including applied and reaction
and are a necessary step in solving for static equilibrium
a reaction force that is perpendicular to the surface the object touches.
have both magnitude and direction and trigonometry
can be used to break them down into x and y components.
Fx = F
cos(θ) and Fy = F
* sin(θ) and θ = tan-1(Fy/Fx)
Solving for Static Equilibrium
1. Assume the body is rigid.
2. Choose a rotational point (with most unknowns go through it) and solve for Σ M = 0
3. Then solve for Σ Fx = 0, and Σ Fy = 0
Define a Problem
Identify a problem that exists. Determine the root cause. Gatherinformation
Present ideas in group. Generate and record ideas. Seek quantity not quality. Keep the mind alert through rapidly paced sessions.
Research and Generate Ideas
Analyze the reasons for the need, want, or problem.
Investigate who or what it is that is affected, and consider the need, want, or problem from their perspective. Research any existing solutions, and identify why they are not adequate or appropriate. Listen to clients to solve problems that they have discovered. Perform market research to determine if a want or need exists and
warrants the development of a design solution.
Identify Criteria and Specify Constraints
Identify the end user if the client is not. Redefine the problem to the agreement of both client and engineer. Identify what the solution must do, and the degree to which it will be pursued. Identify the limitations within which the engineer must perform his/her duties. Compile the information into a design brief.
Initiate further development of brainstorming ideas with
constraints and tradeoffs considered. Explore alternative ideas based on further knowledge and technologies.
Develop a Design Proposal
Develop detailed and annotated sketches. Determine
the type(s) of material from which the solution will be constructed. Make computer
models. Create technical drawings from the computer model(s).
Make a Model or Prototype
Make study models (scaled models or mock-ups). Fabricate a functional prototype.
Test and Evaluate the Design using Specifications
Test the prototype under controlled conditions. Test the prototype under actual conditions. Record the results.
Evaluate results to determine if problems exist and further work is needed.
Refine the Design
Reassess the validity of the design criteria and make adjustments to the design brief, if necessary. Work through the design process until the solution satisfies the design criteria. Update the documentation of the final solution.
Create or Make Solution
Determine Custom/Mass Production. Consider
Communicate Processes and Results:
Present oral presentations with visual aids
(computer generated slide show, models, prototype). Develop written reports with
appropriate graphic documentation (charts, graphs, technical drawings, renderings,
etc.). Market the Product. Distribute.
are the substances with which all objects are made, each
with its own physical and chemical properties.
one type of atom - cannot be broken down
multiple elements chemically bonded.
multiple elements or compounds not chemically
metallic, ceramic, organic, polymeric, and composite.
such as machining, casting, molding, and joining convert raw materials into consumer goods.
an important considerations when choosing materials.
is based upon mechanical, thermal,
electromagnetic, and chemical properties as well as cost.
Tensile Stress Test
Measures the deformation and breaking point of a test sample under static
Brinell or Rockwell hardness measures a material's resistance to a probe creating
a crater in it.
properties such as density and conductivity may be tested without damaging the material, but others such as strength and hardness require destructive tests.
(σ) Externally applied - depends on force and material's shape = F/A for tensile stress.
(ε) material's response to stress = change in length / original length
(δ) elongation - how much the length of a sample changes under stress
Linear portion of stress / strain curve. Material isn't permanently changed.
(Proportional limit or Yield point) Plastic deformation (permanent change) starts to occur.
area under the linear portion of the curve. Measure the energy needed topermanently deform the material
Ultimate Tensile Strength
maximum tensile stress, the peak of the curve.
Amount of plasticity before fracture, measures how much the material can be stretched.
Modulus of Elasticity:
(E) a measure of how much a material resists stretching = σ/ε also =PL/Aδ
P =axial force
L= original length
A= cross sectional area.
always has some error - large samples can be characterized using statistics.
Mean (sum/# of samples), median (middle value) or mode (most common
value) gives us an idea of the true value.
a graphical representation of a program.
• Rectangle: process or action
• Rounded Rectangle: start or end
• Parallelogram: input (from real world to program) or output (from program to the
• Rhombus: decision or a branch
No feedback, relies on timing, un-repeatable
feedback tells program it is done, more repeatable
no connection until switch is pressed
connection until switch is pressed
straight line distance and direction from initial point
a scalar quantity describing distance traveled / time
a vector quantity with both speed and direction
a change in velocity per unit time.
will cause a constant acceleration (ignoring air resistance) of-32.2 ft /sec 2 or -9.8 m/sec2
a non-powered object moving through the air - its final
displacement can be calculated from its initial velocity. Its x- component of velocity is constant while the y component changeddue to gravity.
θ )/ -g
relies on pressure of a liquid or a gas to transmit force
over great distances, multiply an input force, and increase the distance that an output will move.
uses gas - faster, cleaner, requires a lubricant
uses a liquid - stronger, more precise, higher
Basic components of Hydraulics and Pneumatics
of a fluid power systems include a reservoir or
receiver, a pump or compressor, a valve, and a cylinder.
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