## Simple Machines B/Compound Machines C

JonB
Coach
Posts: 283
Joined: March 11th, 2014, 12:00 pm
Division: C
State: FL

### Re: Simple Machines B/Compound Machines C

How does efficiency in pulleys work anyway? My logic (which may not make sense since the system is stable) was that as the rope is pulled through the pulley, it loses 10% of its tension, so the right side ropes need more tension than the left side.
I can best explain this with an example:

In the following image, the left pulley is assumed to be 100% efficient and the right pulley 1% efficient (some arbitrary number showing great inefficiency)
You can clearly see that the left pulley would only remain stationary if the two masses are equal; this isn't the case with the right pulley. For example, if the source of the right pulley's inefficiency was rust (illustrated rather horribly in Paint), then it is reasonable to assume that the right pulley could remain stable as shown, with unequal masses on either side.
That is the basis for my reasoning that pulley inefficiency does carry over into the stationary case.
paintshop.png (6.08 KiB) Viewed 2603 times

Unome
Moderator
Posts: 4122
Joined: January 26th, 2014, 12:48 pm
State: GA
Location: somewhere in the sciolyverse

### Re: Simple Machines B/Compound Machines C

How does efficiency in pulleys work anyway? My logic (which may not make sense since the system is stable) was that as the rope is pulled through the pulley, it loses 10% of its tension, so the right side ropes need more tension than the left side.
I can best explain this with an example:

In the following image, the left pulley is assumed to be 100% efficient and the right pulley 1% efficient (some arbitrary number showing great inefficiency)
You can clearly see that the left pulley would only remain stationary if the two masses are equal; this isn't the case with the right pulley. For example, if the source of the right pulley's inefficiency was rust (illustrated rather horribly in Paint), then it is reasonable to assume that the right pulley could remain stable as shown, with unequal masses on either side.
That is the basis for my reasoning that pulley inefficiency does carry over into the stationary case.
paintshop.png
Ok... I sort of get it. Anyway, the first person that gets here can ask a question.
Userpage
Chattahoochee High School Class of 2018
Georgia Tech Class of 2022

Opinions expressed on this site are not official; the only place for official rules changes and FAQs is soinc.org.

UTF-8 U+6211 U+662F
Exalted Member
Posts: 1518
Joined: January 18th, 2015, 7:42 am
Division: C
State: PA

### Re: Simple Machines B/Compound Machines C

How does efficiency in pulleys work anyway? My logic (which may not make sense since the system is stable) was that as the rope is pulled through the pulley, it loses 10% of its tension, so the right side ropes need more tension than the left side.
I can best explain this with an example:

In the following image, the left pulley is assumed to be 100% efficient and the right pulley 1% efficient (some arbitrary number showing great inefficiency)
You can clearly see that the left pulley would only remain stationary if the two masses are equal; this isn't the case with the right pulley. For example, if the source of the right pulley's inefficiency was rust (illustrated rather horribly in Paint), then it is reasonable to assume that the right pulley could remain stable as shown, with unequal masses on either side.
That is the basis for my reasoning that pulley inefficiency does carry over into the stationary case.
paintshop.png
Ok... I sort of get it. Anyway, the first person that gets here can ask a question.
Extremely simple question:
What is the "law of the lever?"

jkang
Member
Posts: 107
Joined: October 17th, 2014, 8:49 pm
State: TX

### Re: Simple Machines B/Compound Machines C

What is the "law of the lever?"
d1F1 = d2F2, where d = distance from the fulcrum and F = force applied
UT Austin '19
Liberal Arts and Science Academy '15

UTF-8 U+6211 U+662F
Exalted Member
Posts: 1518
Joined: January 18th, 2015, 7:42 am
Division: C
State: PA

### Re: Simple Machines B/Compound Machines C

What is the "law of the lever?"
d1F1 = d2F2, where d = distance from the fulcrum and F = force applied
$d_1F_1 = d_2F_2$

jkang
Member
Posts: 107
Joined: October 17th, 2014, 8:49 pm
State: TX

### Re: Simple Machines B/Compound Machines C

Another pretty simple question: Identify all of the simple machines in a nail clipper (include different classes of levers, if applicable).
UT Austin '19
Liberal Arts and Science Academy '15

mjcox2000
Member
Posts: 120
Joined: May 9th, 2014, 3:34 am
State: VA

### Re: Simple Machines B/Compound Machines C

2 wedges, 1 second class lever, 2 third class levers. (That dotted line is a pin connected to the bottom 3rd class lever, going through the top one, and connected to the 2nd class lever.) There's a spring keeping the two 3rd class levers apart - that isn't a simple machine, but it's part of the resistance, so I thought I'd mention it. Effort is applied at the long end of the 2nd class lever and the vertex of the two 3rd class levers.
MIT ‘23
TJHSST ‘19
Longfellow MS
2019:
Circuit Lab: 1st
Thermodynamics: 2nd
Sounds of Music: 5th
Mission Possible: 6th

2018:
Code Busters (trial): 1st

2015:
Simple Machines: 2nd
SumoBots (trial): 2nd

2014:
WIDI: 2nd
Simple Machines: 3rd

jkang
Member
Posts: 107
Joined: October 17th, 2014, 8:49 pm
State: TX

### Re: Simple Machines B/Compound Machines C

Nail clipper diagram.jpg
2 wedges, 1 second class lever, 2 third class levers. (That dotted line is a pin connected to the bottom 3rd class lever, going through the top one, and connected to the 2nd class lever.) There's a spring keeping the two 3rd class levers apart - that isn't a simple machine, but it's part of the resistance, so I thought I'd mention it. Effort is applied at the long end of the 2nd class lever and the vertex of the two 3rd class levers.
UT Austin '19
Liberal Arts and Science Academy '15

mjcox2000
Member
Posts: 120
Joined: May 9th, 2014, 3:34 am
State: VA

### Re: Simple Machines B/Compound Machines C

How do actual mechanical advantage and ideal mechanical advantage differ? When would one want to know IMA instead of AMA, and vice versa? (This wasn't original - it was on our state test - but I thought it was not a bad question.)
MIT ‘23
TJHSST ‘19
Longfellow MS
2019:
Circuit Lab: 1st
Thermodynamics: 2nd
Sounds of Music: 5th
Mission Possible: 6th

2018:
Code Busters (trial): 1st

2015:
Simple Machines: 2nd
SumoBots (trial): 2nd

2014:
WIDI: 2nd
Simple Machines: 3rd

finagle29
Exalted Member
Posts: 51
Joined: January 28th, 2013, 11:37 am
State: PA
Location: Caltech

### Re: Simple Machines B/Compound Machines C

AMA is the actual mechanical advantage delivered by the machine defined as $\frac{\mathrm{F_{out}}}{\mathrm{F_{in}}}$.  IMA is the theoretical maximum mechanical advantage able to be delivered by a machine in a frictionless environment defined as $\frac{\mathrm{d_{in}}}{\mathrm{d_{out}}}$.  One may want to know IMA instead of AMA because IMA gives information about the geometry of the simple machine which is useful in doing theoretical studies or replicating a simple machine.  One may want to know AMA instead of IMA when doing work with an actual simple machine and its performance is necessary in determining an unknown quantity (energy problems involving a ramp for example)
Bayard Rustin HS Alum

2013 Events: Thermo, Circuit Lab, Experiment, Robot Arm
2014 Events: Circuit Lab, Experiment, TPS, Mat Sci, Astro
2015 Events: Astro, Chem Lab, Compound Machines, Experiment, Time, TPS
2016 Events: Astro, Cell Bio, Chem Lab, Electric Vehicle, Time, Protein Modeling, Wind Power