Transcript 24. Ohm`s Law

1a. Technology is the application of knowledge, tools,
and skills to solve problems and extend human
capabilities.
b. A technology system is a group of subsystems working
together to solve problems and extend human
capabilities.
c.An artifact is something made by humans for a practical
purpose.
Question 2: 12 steps of design process.
1. Defining a problem
2. Identifying criteria and specifying constraints
3. Researching and generating ideas
4. Brainstorming
5. Exploring possibilities
6. Selecting an approach
7. Developing a design proposal – purpose is to
communicate final design and steps to construct it.
8. Making a model or prototype
9. Testing and evaluating the design, using specifications
10.Refining the design
11.Creating or making it
12.Communicating processes and results
3. Principle: a law of nature underlying the working of an
artificial device
4.Mechanical technology: the technology of putting together
mechanical parts to produce, control, and transmit motion.
5.Machines: artifacts that transmit or change the application of
power, force, or motion.
6.Machines can be simple or complex. Complex machines are
made up of simple machines.
7.Core technologies are the “building blocks” of all technology.
8 a. Door latch: mechanical, structural, material
b. Fan: mechanical, electrical, structural, material
c. Crankshaft: mechanical, material, structural
d. Battery: structural, electrical, material
e. Thermostat: material, electronic, thermal
f. Cylinder: structural, material
g. Gas tank: structural, material
9.Simple machines work on the principle of the lever and
the inclined plane.
10. Lever: lever, pulley, wheel and axle;
inclined plane, wedge, screw
Inclined plane:
11
12 F x d = WORK
13 Wo / Wi = EFFICIENCY
14 A systematic application is an organized or established
procedure, a set of steps.
15 “A” would be easier to push down.
16 The load of “B” will travel the greater distance.
17 A force multiplier is a machine that increases the force
applied to the work at hand.
A distance multiplier is a machine that increases the distance
the load moves.
“A” above is the force multiplier. “B” is the distance multiplier.
18. Mechanical Advantage (M.A.) is the number of times a
mechanical device multiplies an applied force. The equation
for M.A. is
DF / DL
and
L / F.
19. A pulley is a mechanical device that is an adaptation of a
wheel and axle. To find M.A. of a pulley, count the total
number of strands supporting the load.
20. A fixed pulley is a pulley attached or fixed to a strong
structural member (system does not move). MA = 1.
21. A movable pulley is a pulley that is free to move since it is
attached with a strand to a fixed structural member. MA = 2.
22. A block and tackle is a system of three pulleys: 2 fixed and
1 movable. MA = 3.
FIXED
MOVABLE
BLOCK and TACKLE
23.Electrical Technology: the technology of producing, storing,
controlling, transmitting and getting work from electrical
energy.
24. Ohm’s Law –
V=IxR
Joule’s Law –
P=I x V
25. Amperes – measures current;
Volts – measures electric potential (voltage);
Ohms – measures resistance.
26
P = I2 x R
27
P = V2 / R
28Electrons – Negative; Protons – Positive; Neutrons – Neutral
29
A circuit consists of (at least) a power source, a
conductor, and a resistor.
30
Materials with “free electrons” are considered conductors
(most metals); materials with “bound electrons” are considered
insulators (wood).
31Electrons flow from the negative terminal of the power supply
to the positive terminal of the power supply.
32 Voltage is the electric potential of an electric circuit;
Current is the rate of flow of electrons through a conductor;
Resistance is the resistance to electron current (resisting an
electric current generally creates heat).
33Ohm’s Law – V = I x R; Joule’s Law – P = I x V
34A schematic is a diagram that represents the components of
a system without using actual pictures.
35DC Power AC Power Resistor
Switch
Conductor
36 Sketch schematics and write equations for 4 resistors in
series and in parallel
37
A smaller-diameter wire has more resistance than a largerdiameter wire because there is a wider “path” for electrons to flow
in a larger-diameter wire. The wider the “path,” the lesser the
resistance.
38
1,000 W = 1 kW. 1,000 V = 1 kV.
39
Ohm – German mathematics teacher/professor, Ohm’s
Law: V = I x R.
Joule – English physicist, Joule’s Law: P = I x V.
Faraday – English physicist and chemist; discovered that
magnetic fields induce electric currents.
40 Conductors: Copper, Iron, Aluminum; Insulators: Glass, Wood,
Cotton
41 The electromagnet on the electric motor was the bolt and the
coil of wire wrapped around it.
41The electromagnet on the electric motor was the bolt and the
coil of wire wrapped around it.
42
43 An electromagnet is a coil of wire and some metallic artifact
(like an iron nail or bolt) that creates a variable magnetic field
that can be turned on and off.
441) An electromagnet can be turned on and off;
2) the strength and direction of the magnetic poles of an
electromagnet can be controlled by altering the strength and
direction of the electric current creating the magnetic field.
45The purpose of a switch is to provide a means to open and
close (turn on and off) an electric circuit.
46. Fluid technology is the technology of using fluid, either gas
(pneumatics) or liquid (hydraulic) to apply force or to transport.
47. Boyle’s Law: the pressure and volume of an ideal gas are
inversely proportional when temperature is constant.
48. Pressure and volume are inversely proportional. This means
that P a 1/V and V a 1/P (pressure is proportional to 1/V and
volume is proportional to 1/P).
49. A pneumatic technology is a fluid technology using a gas. A
hydraulic technology is a fluid technology using a liquid.
50. Aerodynamics deals with the motion of air and other gaseous
fluids; air and gases are fluids and are used in fluid technology.
51
1) All fluid technologies use a fluid, either gaseous or liquid; 2)
All fluid technologies contain a pressure difference that creates a
net force.
52 Thermal Technology – the technology of producing, storing,
controlling, transmitting and getting work from heat energy.
Thermodynamics - the science dealing with internal
energy, heat, and work
Photon – a particle of light
Conduction – the transfer of heat through a substance
by collision of molecules.
Convection – is the transfer of heat by movement of a
fluid.
Radiation – the transfer of energy by electromagnetic
waves.
53. Furnace, Hot water heater, Toaster, Insulation, Heat
exchanger, Refrigerator, Hot air balloon, Fan, Engine cooling
system, Oven, Blow-dryer, Thermos, Heat shrink, Styrofoam,
Radiator, Blanket, Winter jacket, Wool socks
54. The more powerful radiation heat is in the form of infrared
light, which we cannot see with our natural eyes. Therefore,
infrared photography allows us to “see” the heat given off by
objects even if the material is not hot enough for there to be a
55. Natural Convection: Fluid surrounding a heat source receives
heat and rises (due to lower density)
Surrounding cooler fluid moves in to replace it. Cooler fluid is
heated, rises, and cycle continues.
2) Forced Convection: Fans or other means are used to propel
a fluid. An convection current is induced. Car
engine and A/C are examples
56. White, Blue, Yellow, Orange, Red
57. Solid, Fluid, No medium
58. Thermal energy flows from regions of high temperature to
regions of lower temperature.
59. The driving force for heat transfer is a difference in
temperature.
60. The more accurate way of saying an object is “cold” is saying
that it lacks heat.
61 1) Conduction: the transfer of heat through a substance
(typically a solid) by collision of molecules.
2) Convection: the transfer of heat by movement of a fluid.
3) Radiation: the transfer of heat by electromagnet waves
73.The technology of putting mechanical parts and materials
together to create supports, containers, shelters, connectors,
and functional shapes.
74.Tension structures: spider web, climbing rope. Compression
structures: chair legs, book shelves
75. Father of modern science, Father of modern physics, First
modern engineer.
76. 1) Inertia, 2) F = ma, 3) Action/Reaction. Structural
technology based mainly on #3.
77. The earth is pushing up at you with 150 lbs. (or whatever else
your weight may be).
78. Type, size, shape, and placement of material determines its
strength.
79 Beams are horizontal structural members
Posts are vertical structural members,
Trusses are an assemblage of beams forming a rigid framework.
80. The goal of structural members is to be as light as possible
without being too flexible or unstable.
81. Tacoma Narrows bridge (1940), Challenger Space Shuttle
(1986), Columbia Space Shuttle (2003), Chernobyl Nuclear
Reactor (1986), 2007 Missouri bridge collapse
82. Trial and Error.
83. Common Sense.
84 1) Compression: a pushing force;
2) Tension: a pulling force;
3) Torsion: a twisting force;
4) Shear: a sliding force.
85 Deflection is bending that results from both tension and
compression acting on a structural member at the same time.