M04, L1 Friday, August 27, 2010 9:15 AM
Voice Thread: http://voicethread.com/?#u1020010.b1286887.i6899657
Current slide set (10/20/10)
VoiceThread has about 30 minute running time (has some math; no math worked out on the math problem slides)
Notes in this text color are on exam/quiz.
The Distinction Between Science, Applied Science, and Technology
Motivation (reasons behind) different between each • Science motivated purely by curiosity = wants knowledge to satisfy curiosity • Applied science = experiments aimed at trying to find something useful (building process, doing job to make something easier) • Technology = invention of new machine or process to make life easier (result of applied science, result of science, result of accident)
Technology as result of accident = ancient
General Science Page 1 ○ Technology as result of accident = ancient Egyptians (Imhotep) putting moldy bread on wounds (had tried other methods that didn't work, this one did)
○ Technology as result of applied science = Blaise Pascal (1642) wanted to make job of adding and subtracting numbers easier; after years of experiments came up with adding machine (beginning of computer), using scientific method . Other machines eventually could also multiply and divide . Still other machines could "remember" calculations . These machines made of gears, rods, shafts
. First electronic computer (1946, U of Penn)= John Eckert & John Mauchly invented ENIAC (Electronic Numerical Integrator and Computer) used 18,000 or 19,000 vacuum tubes(electronic devices) and fit into entire it into 30 ft x 50 ft room (U of Penn) to make several 100 multiplication steps a second (fast compared to earlier machines, huge and very expensive) . Bad vacuum tube pic = replacing one of ENIAC's vacuum tubes . Applied scientists worked on reducing size & cost of computer (making smaller, cheaper vacuum tubes; making replacement) □ 1948 - 3 Bell Telephone Laboratories (became AT&T) scientists (Walter Brattain, John Bardeen, William Shockley) developed transistor - could do job of vacuum tube at much cheaper price, also much smaller = small, cheap computers - start of computer age □ ------Even in a copyright questionable situation, you can drop in an image, so here is a vacuum tube one for dropping in live time …
Technology as result of science
General Science Page 2 Technology as result of science • X-rays (1895) discovered by German scientist Wilhelm Conrad Roentgen - trying to experiment with electricity to understand it -Passing electricity through tube partially filled with gas -Tube inside black cardboard, yet when electricity moved through tube, nearby screen glowed -Hypothesized tube giving off rays when electricity passed through, but didn't know what they were so he called then "X-rays" -Did more experiments - found X-rays could make images on photographic film (like light does)
Medical scientists began using X-rays =images inside human bodies, find bullets inside shooting victims, diagnose problems with bones & internal organs with more advanced technology
• As Application Share to navigate: http://www.colorado.edu/physics/2000/index. pl (X-ray interactive of hand) - direct link at … http://www.colorado.edu/physics/2000/index. pl ○ At site find Einstein's legacy on right, click "here", then "X-rays applet"
Simple Machines
Skip the following since it will take too much time to go through the tutorial. It will be useful in newsletter though. http://www.cosi.org/files/flash/simpMach/sm1. swf
Technology & applied science
Simple machine = a device that reduces the amount of force needed to perform a task or changes the direction of a force (make tasks easier)
Force = a push or pull that changes the motion of an object
Force examples = pushing stalled car (enough force will change motion of stalled car); if car rolls downhill to service station - use brakes - apply push to change motion of car, to stop
6 basic simple machines = lever, wheel & axle, pulley, inclined plane, wedge, screw (Renaissance scientists defined)
Any non-electronic machine is combination of simple machines
Renaissance - these 6 were known
General Science Page 3 Renaissance - these 6 were known
Lever
Lever - simple machine that magnifies force or motion
has 3 parts: fulcrum, effort, resistance
Made of rigid bar that rotates around fixed point = fulcrum
Effort of lever = force being applied to the lever
Resistance of lever = weight that's being lifted
Mechanical Advantage
Mechanical advantage = the amount by which force or motion is magnified in a simple machine
in a lever MA determined by distance between effort and fulcrum compared to distance between resistance and fulcrum
No MA if fulcrum in middle of lever
MA = (distance from fulcrum to effort) / (distance from fulcrum to resistance)
Lever
Practice Problem:
General Science Page 4 Practice Problem:
MA = (distance from fulcrum to effort) / (distance from fulcrum to resistance)
EX: fulcrum 6 inches from resistance; 60 inches from effort MA = 60/6 = 10
Practice Problem:
MA = (distance from fulcrum to effort)/(distance from fulcrum to resistance)
MA = 100/5 = 20
Practice Problem:
MA = (distance from fulcrum to effort)/(distance from fulcrum to resistance)
MA = 3/1 = 3
Practice Problem:
General Science Page 5 Practice Problem:
1st- & 2nd-class levers = effort is magnified by 10; for 3rd-class levers = resistance moves at 10 times the speed on effort
3 different classes of levers difference where fulcrum is relative to effort and resistance
First-class lever (4.1 p88) (not really great lever) Fulcrum positioned between effort and resistance
Second-class lever (4.2 p90) Fulcrum at one end of bar and resistance between fulcrum and effort
Third-class lever (4.2) fulcrum at one end of bar & effort between fulcrum & resistance
Nature of MA different
1st class Magnifies: effort, also changes direction of effort vs force: change
2nd class Magnifies: force direction of effort vs force: No change
3rd class Magnifies: speed direction of effort vs force: No change
Common Examples
General Science Page 6 Common Examples
First Class Levers: Pictures: See Saw Additional:: scissors, pliers = first- class levers
Second-class lever: pictured = nutcracker Additional: wheelbarrow
Third class lever: Pictured: Toenail clippers Additional: your forearm
The Wheel and Axle (4.4 p93)
Large circular wheel attached to smaller cylinder (solid tube) must turn the wheel more than the axle turns (or axle turns more slowly than the wheel)= drawback Wheel turns, so does axle; axle turns, so does wheel
2 car examples:
Cam Shaft: force applied to turn axle, causes wheel to turn = engine turns axle of car's wheels, causing wheels to turn = car moves forward
Steering Wheel: force used to turn wheel (more effort), then axle turns = steering wheel - driver turns wheel, and axle turns
Mechanical Advantage Calculations:
MA = need to know diameter of wheel and diameter of axle
Diameter = the length of a straight line that travels from one side of a circle to the other, while passing through the center of the circle
General Science Page 7 while passing through the center of the circle
Diameter of wheel bigger than the diameter of axle
If turning wheel = MA increase force (18- wheeler truck's wheel much bigger than passenger car's)
If turning axle = MA increase speed (engine to axle)
Race car's tires bigger than passenger car's = higher MA = higher speed MA = (diameter of wheel)/(diameter of axle)
MA = 24/2 = 12
The Pulley (4.5 p96)
General Science Page 8 The Pulley (4.5 p96)
Pulley = grooved wheel that rotates freely on a frame (block) Works by laying rope in pulley's groove; pull down 1 end of rope, other end goes up
Mechanical Advantage: No MA for single pulley by itself; DOES change direction of force; usually easier to pull down that pull up
Series of pulleys does give MA Block and tackle - using multiple pulleys - 1 fixed pulley and at least 1 movable pulley = number of pulleys = MA
[picture = ship's block]
MA = number of pulleys MA = 4
(will use 4 times the rope length)
"don't get something for nothing" if pulley has MA = 2, and pull object 5 ft , will use 10 ft of rope = "pay" by using force over longer distance
Lever = if fulcrum closer to resistance than effort, have to push lever farther than resistance moves up EX: if MA=3 (1st & 2nd classes) - force exerted magnified by 3, but push or pull load 3 times as far as lifted
3rd class lever or wheel & axle (magnify speed) - "Pay" for magnified speed by using a lot more force; if 3rd class lever MA = 3, load moves 3 times faster than effort's speed, but effort 3 times larger than move without lever
Simple machine to magnify force = apply force over longer distance Simple machine to magnify speed = apply much
General Science Page 9 Simple machine to magnify speed = apply much larger force
The Inclined Plane ramp, slope (even stairs)
Mechanical advantage = (length of slope)/(height)
"pay" = have to push load farther (but not as hard)
[picture = Roman inclined plane]
MA = (length of slope) / height
MA = 8/2 = 4
Drawback for 10 times longer = move 10 times the distance
General Science Page 10 The Wedge (4.7 p.101)
Often confused with inclined plane (look alike) used differently
Inclined plane = Eases force required to lift a load Wedge = Magnifies force being applied
Ex: used to split firewood - pointed end of wedge placed in contact with log, hammer used to hit opposite end
Knife = edge of knife cuts into object with much greater force than you used to push (also scissor blades, front teeth are wedges)
Double wedge = modified version of wedge (4.8 p. 101) - 2 wedges put together
MA calculated same for wedge or double wedge
"pay" = to get magnified force, must apply a force over a longer distance MA = (length of slope)/height
Mechanical advantage = (length of slope)/ (height) calculation examples
Single has more MA
General Science Page 11 The Screw 94.9 p, 102)
Inclined plane wrapped around the axle of wheel and axle (paper triangle around pencil?)
Inclined planes on screw called threads Vertical distance between threads = pitch of the screw
Mechanical advantage = (circumference) / (pitch) Circumference = the distance around a circle, equal to 3.1416 times the circle's diameter
'pi" approximately equal to 3.1416
Calculations
Typical pitch = 0.1 inches; screw head might be 0.2 inches in diameter calculation examples & screwdriver
Circumference = 3.1416 x (diameter) Circumference = 3.1416 x 0.2 =0.62832
MA = (circumference) / (pitch) MA = (0.62832)/(0.1)=6.2832 MA if put in the screw by hand (hard to do)
Even easier with screwdriver = screwdriver's circumference is much larger than the screw's. When using screwdriver , using the circumference of screwdriver, not screw
Diameter of screwdriver typically 1 inch
Circumference = 3.1416 x (diameter) Circumference = 3.1416 x 1.0 = 3.1416
Mechanical advantage = (circumference) / (pitch) Mechanical advantage = 3.1416 / 0.1 = 31.416 31.416
Larger diameter (fatter) the screwdriver = more MA (not length)
General Science Page 12 Screwdriver itself is simple machine = wheel and axle
A: MA= circumference/pitch Circumference = 3.1416 * diameter
Circumference = (3.1416)*(0.30) = 0.9425 MA = 0.9425/0.05 = 18.85
B: Circumference = (3.1416)*(1.5) = 4.7124 MA = 4.7124/0.05 = 94.248
MA= circumference/pitch Circumference = 3.1416 * diameter Circumference = 3.1416 * 1.0 = 3.1416 MA = 3.1416/0.02=157.08
General Science Page 13 Quiz link is http://www.virtualhomeschoolgroup.com/mod/quiz/view.php?id=17811
General Science Page 14