Work Made Easy: Comparing the Efficiency of Simple Machines

***Show "Simple Machines" video (see notes, 
simple-machines_bill-nye.txt)***

Follow-up demos: Force-distance trade-off. Demo door with two handles: 
Vernier "Logger Pro" software interfaced with LabPro and dual-range force 
sensor (two ranges: ±10N or ±50N).

[begin sidebar notes]

A Door is a Lever

Vernier Dual-Range Force Sensor: +/-10N; +/-50N

Set-up laptop & lab interfacing equipment on student deskette. Set for
+/-50N; connect to LabPro. Launch Logger Pro; Insert "Meter" (resize to
full-screen).

Tie a loop of string around both door knobs; attach hook (on end of force
probe) to loop of string and pull steadily. Outer doorknob = ~10N max.;
inner door handle (near hinges) = ~30N max.

Google Search: door + lever + class

lever: Definition and Much More From Answers.com
http://www.answers.com/topic/lever

P.O.D. - 13 APR 2005
[Two door handles....]
13 APR 2005

Q. You may have noticed the door to the classroom has two handles: one 
located near the outer edge of the door; and one located near the inner 
edge of the door (closer to the hinges). Which one of the two door handles 
will require less effort force (F-sub-e) be exerted in order to close the 
door? Explain your answer.
A. The handle near the outer edge; the force-distance trade-off 
explains...

[end sidebar notes]

75-25 lever, F(e) = ~1N, MA = ~5x; four-rope block-and-tackle pulley 
system, F(e) = ~1.25N (500g/4), MA = ~4x. Both simple machines multiply 
the effort force significantly. Use 75-25 lever to demo what happens when 
you place the resistance of the 75-side (the effort force is MUCH >10N!). 
[Use force sensor to measure actual effort force. I estimate it should be 
~15N (MA = .333; 5 x 3 = 15). In fact, it was ~17.2N, as measured with a 
Vernier force sensor.]

Assembly details re: block-and-tackle pulley system:
Two single pulleys (top) plus double pulley (bottom)
04_red/06_work_made_easy/pull-ease/No1_Activity/bt4.gif
04_red/06_work_made_easy/pull-ease/No1_Activity/bt7.gif (detail, double 
pulley)

Follow-up P.O.D.s (or "Bell WORK"):
Q. What type of simple machine is a see-saw?
A. Lever
Q. When "playing" on a see-saw, how could a small child (on one side) lift 
a large adult (on the other side)?
A. Using a 500g mass to simulate the small child and two 500g masses to 
simulate the large adult, an equal-arm see-saw (meter stick with fulcrum 
at 50cm) is balanced with the two masses placed at ~25cm from one end of 
the meter stick.

[Placeholder text re: planning notes.]

Note to L. Chin: Five (5) pages of activity questions is EXCESSIVE! Select 
most important questions; delete other questions (or prepare worksheet(s) 
of practice problems). Failing ISD-authorized revision, omit repetitive or 
unimportant questions.

==
Notes from Glencoe _Physical Science_
p. 186 THE SIMPLE MACHINES

The fixed point of a lever is called the FULCRUM. The part of the lever on
which the effort force is applied is called the EFFORT ARM. The part of
the lever that exerts the resistance force is called the RESISTANCE ARM.

p. 187 FINDING THE IDEAL MECHANICAL ADVANTAGE (IMA)

You can also use the lengths of the arms of a lever to find the IMA of the
lever. The length of the effort arm is the distance from the fulcrum to
the point where the effort force is applied. The length of the resistance
arm is the distance from the fulcrum to the point where the resistance
force is applied. The following equation, which assumes no friction, can
be used to find the IMA of any lever.

IMA = length of effort arm/length of resistance arm = L(e)/L(r)

Demo 1 - Lab Set-Up: 50 cm/50 cm = 1x

Demo 2 - Modified Lab Set-Up: 75 cm/25 cm = 3x

--
Block and tackle
http://en.wikipedia.org/wiki/Block_and_tackle
Note: block = set of pulleys; tackle = entire system (pulleys + rope)
External link
Model and demonstration: Pulley System
http://www.walter-fendt.de/ph14e/pulleysystem.htm

==ASSESSMENT==

P.O.D.s

[show B.C. comic: extras/work_comic/bc0619g.gif]
Q. Change only ONE word in the comic "balloons" in order to make the 
punchline completely consistent with the definition of "work."
A. Since W = F x d, "...Dad gets BUSY." should be changed to "...Dad gets 
MOVING."

--
Motion-Gravity-Friction Quest: 20 questions; use #13-17 to assess PB13, 
Newton's Laws.

--
Work & Power Quiz: 10 questions; use #1, #3, #5, #6, #7 to assess PB14, 
Forces and Motion/Work.
"Reference Tables" (RSLG, p. 43, "Important Terms and Symbols for 
Calculating Efficiency")