Daniella
C Block
Mr. Harrington
"They Kept Calling Her Pushy, Until She Became a Pulley"
Abstract/Purpose:
The purpose of this lab was to observe the mechanical advantage of pulley systems. In this lab,
knowledge and understanding of simple machines were portrayed. The six simple machines. Known to man
are the lever, wheel and axle, pulley, incline plane, screw, and wedge. Each of these machines achieve one or
more function(s), well known as advantages. One of the machines that helps reduce work is the pulley, which
consists of a wheel, block and rope. It was observed that the double fixed-double moveable pulley was the
most effective pulley because of its mechanical advantage, which turned out to be an important aspect of this
simple machine.
Introduction:
A machine is a device that is used to help make work easier. How did machines start, though?
Machines started long time ago in the ancient world when construction began and a man/woman wanted to
find an easier way to pick up a block. They grabbed a stick and put it under the object and pushed down on it,
lifting it up. This is exactly what simple machines are known for, they help accomplish work in a better way.
The six simple machines that help with work are: lever, wheel and axle, pulley, inclined plane, screw and the
wedge. The lever is known as a bar that rotates around a fixed point known as the fulcrum. The wheel and
axle consists of two things: a wheel that is attached to a smaller wheel called an axle. Pulleys are consisted of
grooved wheels that freely turn in a "block", usually with a rope through it. There is also the inclined plane,
which is a sloped surface that helps move something from a lower to higher elevation. The wedge is a
modification of the inclined plane that is used to separate/hold devices, well as the screw, which is known as a
"circular ramp." Simple machines are truly a main aspect of today's construction process.
Each simple machine accomplishes one or more function(s), better known as advantages. The four
advantages of a simple machine are: transferring a force from one place to another, changing the direction of a
force, increasing the magnitude of a force, and or increasing the distance or spread of a force. All machines
have different purposes, but the main reason why all these functions are advantages is because the reduce the
amount of "work". Each one has a different purpose, but one thing they all share is reducing the amount of
"work", or effort being done. Work is when an object is moved a distance using force, and when the object
and the force are in the same direction (formula: Work=Force x Distance.) These machines were essential in
order to minimize the amount of labor/work being done by humans.
One of the most helpful machines of all is the pulley. It either helps change the direction of the force,
or to increase the mechanical advantage, depending on the pulley set up. There are two different types of
pulleys: moveables and fixed. The fixed pulley is the one that does not move with the load being moved,
while the movable moves. The single fixed pulley has an MA of 1 and a common for of it is the flagpole
pulley. A zip line is an example of a single moveable pulley with a mechanical advantage of 2. Finally, a
compound pulley (fixed and moveable) has an MA of 2+ and has a common form of a crane pulley. The
mechanical advantage of a simple machine is the when the machines changes the direction of the force
applied to it. The MA is usually measured by counting the amount of ropes pulling up on the object. If the MA
is multiplied by the amount of force applied, then the number that comes out is the amount of force being
applied to the load, measured in newtons. Also, is the MA is 2 then the weight would be a 2:1 ratio meaning
that the weight being pulled is only half. The object is known as the load, and the force being applied is
known as the effort. Out of the things being measured we also have the work output and input. The work
output is the amount of work needed to move the hanging mass, and the input force is the amount of work
exerted to move the hanging mass. Pulleys remain every constructor's secret weapon.
Equipment and materials:
Base
Stand rod
T-connector
Extension rod
Pulley cord
2 single pulleys
2 double pulleys
Spring scale
Mass Hanger
10 mass pieces
Calculator
Meter stick or meter measuring tape
Permanent marker
Procedure:
Look at lab for further details.
Observation/Data:
In this lab, the goal was to see which type of pulley was going to be most effective and help us pull a
person up. The pulleys tested were: single fixed, single moveable, single fixed-single moveable, double fixedsingle moveable, and a double fixed-double moveable. The results varied in this lab from pulley to pulleys,
and the following data was recorded: No. of cords effort force acts on, mass unit, resistance force, resistance
distance, work output, effort force, effort distance, work input, mechanical advantage, ideal mechanical
advantage, and efficiency. By testing these results, it was confirmed that having a double fixed-double
moveable was the best pulley to lift up an object.
Analysis:
When the lab was conducted, there were many reasons why the double fixed-double moveable was
best. The double fixed-double moveable had a mechanical advantage of four (four ropes pulling up), which
meant the weight was a 4:1 ratio. There was a 100 pound person used for this lab. The person who pulled
down the rope in order to lift the load, only had to pull 25 pounds, a fourth of the weight. The person sitting in
the hammock also got a chance to pull himself up. For this type of pulley, 4x the normal amount of rope was
needed because every foot being pulled up meant that a foot was taken from each rope pulling up, using four
feet of rope for every foot moving up. Meanwhile, for the single fixed, since the mechanical advantage was
only one, it was the same weight being pulled, just in a different direction. It did not reduce any work. It was
noted that the best method to pick up a heavy object is with the double fixed-double moveable pulley, or with
the pulley that has the most mechanical advantages.
Conclusion:
This lab portrayed a strong use of knowledge on simple machines, advantages and pulleys. Pulleys are
one of the six simple machines that help reduce the amount of "work" being done, and has more than two of
the four functions known as advantages. Out of the 5 different types of pulleys tested in this lab, we found out
that the double fixed-double moveable was the pulley that required the least effort and had the most
mechanical advantages. Single fixed pulleys were the least helpful and did not reduce any work. The
mechanical advantage is a main factor in determining which pulley requires the least amount of work.
Bibliography:
"Pulleys." Ck12. N.p., n.d. Web. 23 Sept. 2016. <http://www.ck12.org/physical-science/Pulley-in-PhysicalScience/lesson/Pulley-MS-PS/?referrer=concept_details>.
"Simple Machines: Facts." Idaho-to.org. N.p., n.d. Web. 23 Sept. 2016. <http://idahoptv.org/sciencetrek/
topics/simple_machines/facts.cfm>.
In class Nearpod; "Work and Simple Machines", Nearpod. Web. 23 Sept. 2016.