Lab Assignment: Machines and Efficiency Laboratory:
Introduction
20 points
This lab demonstrates the principles of mechanical advantage and efficiency with regard
to simple machines. Mechanical advantage is the ratio of output force to input force.
Efficiency is the ratio of work output to work input. Studying mechanical advantage and
efficiency helps physicists design machines that are most effective at doing their job.
•
•
•
•
Design an experiment you could construct, that might measure the mechanical advantage
and efficiency of a simple machine.
What materials would you use?
What would you measure?
What results would you expect?
What if the results were different; what would that indicate?
Write down your answers; this information will be a part of your lab write-up that you
submit to your teacher.
Lab Assignment: Machines and Efficiency Laboratory:
Description
Developing a Hypothesis:
In this experiment, you will study and compare the mechanical advantage and
efficiency of a pulley with those of an inclined plane.
•
•
Create hypotheses of what you think the results of this experiment will be.
Which machine will have the most mechanical advantage?
Which machine will be the most efficient?
Defend your hypotheses with your knowledge of forces and work. Your answers will
be part of your lab write-up that you submit to your teacher.
Objectives:
1. Measure the work input and output of various machines.
2. Calculate the efficiency of each machine.
3. Compare machines based on their efficiencies, and determine what factors
affect efficiency.
To view the items that need to be included in your lab write-up along with a grading
rubric, please refer to the Guidelines for the Laboratory section in the orientation.
Lab Assignment: Machines and Efficiency Laboratory:
Procedure
Preparation
Read the entire lab procedure and plan the steps you will take.
1.
You will need to use two different websites for this virtual lab. The inclined
plane virtual lab is found at The Ramp Inclined Plane Virtual Lab. Click the
download button and it will download and open on your computer. The pulley
system is found at http://www.compassproject.net/sims/pulley.html
2.
Prepare two data tables in your spreadsheet program. Table 1 is for the
inclined plane lab. Label columns: Trial, Object, Mass (kg), Incline Angle (degrees),
Applied Force (N), Work Applied (J), Distance (m). Table 2 is for the pulley lab.
Label columns Trial, Number of pulleys, Mass (kg), Mass of pulleys (kg), and
Necessary Force (N). The example below shows how to set up your data tables.
Table 1 - Inclined Plane
Trial
Object
Mass (kg)
θ Forced Applied (N)
Work Applied (J)
Distance (m)
Table 2 - Pulley
Trial Number of
pullyes
Load Weight
(N)
Pulley Weight
(N)
Necessary Force
(N)
string
(cm)
load
(cm)
Inclined Plane
1.
Familiarize yourself with The Ramp simulation; follow procedures 1–7 below.
Note that procedure 3 asks you to record the results in your data tables.
1.
The simulation contains an image of a man who can push various
items up a ramp. You can make the man apply force to the objects in several
ways: by clicking and dragging the item itself, by moving the slider labeled
Parallel Force directly to the left of the graph, by clicking the up and down
arrows on the Applied Force button on the far left of the screen or by entering
numbers on the Applied Force button.
2.
In this lab, you will measure Applied Work. Collapse the graph that
shows forces by clicking the minimize button in the top right corner of the graph.
Click the button that says Work Graph. The Applied Work will be shown in
yellow-orange on the graph during trials.
3.
To the right of the graph are different items that you can select for the
man to push across the floor. Notice that the masses of these items are given.
Begin by choosing the file cabinet. Record this as well as its mass in Table 1.
4.
Below the part of the screen where you can choose the object to slide
along the ramp, there is a button you can click to make the ramp frictionless.
Make sure that this button is checked.
5.
Below the Frictionless button, there are two sliders. The top one allows
you to change the position of the "man" along the ramp. You can also type in a
position in the button under the slider. The other slider allows you to change the
angle of incline of the ramp. Begin with an incline of 10 degrees.
6.
To the far left of the graph are buttons that you can use to start a trial
so that the various forces are recorded on the graph. Before the recording starts,
you need to click Go. To clear the graph before a new trial, click Clear. You
must click Go again to start a trial.
7.
In the very top left of the screen, there are numbers that record the
time since you clicked Go, and that tell you the velocity of the object. Make sure
you can locate these buttons, as you will use them in your experiment.
2.
Calculate the Applied Force that will make the object move up the ramp with
constant velocity. Because the ramp is frictionless, the only force pushing the
object down the ramp is the component of gravity that is parallel to the ramp. This
is equal to mg sin theta (θ) where m is the mass of the object, g is the acceleration
due to gravity, and θ is the angle of incline. Calculate this value in Table 1. (Note
that some spreadsheet programs like Microsoft Excel use radians in trigonometric
functions. You can convert degrees to radians by multiplying degrees by π (Pi)
and then dividing by 180. In Excel, use the function Pi() for π; multiply the angle of
incline by the ratio Pi()/180 in order to convert to radians.)
3.
Type the value you calculated for Applied Force into the Applied Force box on
the left of the screen. Move the object to the bottom of the ramp by typing, 0.0, into
the position button. Click Go. Watch the object move up the ramp, and make sure
it moves with a constant velocity, or very close to a constant velocity. Remember
that you can check the velocity of the object by looking at the number in the left top
corner of the screen. Click Pause before the object hits the wall. Record the value
of Applied Work in Table 1. Notice the position of the object under the position
slider. Record this value in Table 1 as well.
4.
Choose two more angles of incline and repeat Steps 5 and 6.
5.
Choose a different object. Repeat steps 5 through 7, using the same angles
of incline that you used for the file cabinet. You should end up with six trials in total.
Pulley
The pulley lab allows you to load masses on a pulley setup and lift the load.
You can change the number of pulleys using the button in the pulley system
section of the lab. You can change the weight of the load by entering values or
sliding the bars on the right of the screen. The virtual lab calculates the force
necessary to lift each load after you make your selections found in the Controls
section at the bottom center. This is the same as input force.
7.
Pick a weight for the load. You should keep these values constant for all of
your trials. Notice that if you create a load that is too heavy, the program will
default to a value it can handle (less than 10 newtons). Record these values in
Table 2.
8.
Start with a 1-pulley (single compound) system. Lift the load by pulling down
on the string. Do this a couple times so that you can see how the load and the
string move.
6.
9.
Record the vertical change in height of the end of the string in Table 2.
Record the vertical change of height of the load in Table 2.
10.
Repeat step 9 using a 2-pulley (double compound) system and a 4-pulley
(quadruple compound) system.
Lab Assignment: Machines and Efficiency Laboratory:
Analysis
Inclined Plane
1.
Organizing Data: For each trial, make the following calculations. You should
add columns to your spreadsheet for the calculations.
1.
the change in height of the object, which is the distance along the
ramp multiplied by the sine of the ramp angle
2.
the output force, which is the same as the weight of the object being
raised
3.
the output work, which is the product of the output force and the
change in height of the object
4.
the mechanical advantage, which is equal to the ratio of the output
force to the input force (or the applied force)
5.
the efficiency, which is equal to the ratio of the work output to the work
input. (Remember that W = F • d)
2.
Analyzing Results: In which trial did the machine perform the most work? In
which trial did it perform the least work?
3.
Analyzing Results: Under what conditions was the mechanical advantage
the greatest? When was it the least?
4.
Analyzing Results: How did changing the mass of the object change the
mechanical advantage of the machine?
Pulley
Organizing Data: Make the following calculations for each trial. You should
add columns to your spreadsheet for the calculations:
1.
the work input, which is equal to the product of the necessary force
and the change in height of the string
2.
the work output, which is equal to the sum of the weights of the pulleys
and the load multiplied by the change in height of the load
3.
the mechanical advantage, which is equal to the ratio of the output
force (the sum of the weights of the pulleys and the load) to the input force (or
the necessary force)
4.
the efficiency, which is equal to the ratio of work input to work output
6.
Analyzing Results: In which trial, did the machine perform the most work? In
which trial, did it perform the least work?
7.
Analyzing Results: Under what conditions was the mechanical advantage
the greatest? When was it the least?
5.
Lab Assignment: Machines and Efficiency Laboratory:
Conclusions
1.
Drawing Conclusions: Based on your calculations, which machine has the
most mechanical advantage: a pulley system or an inclined plane?
2.
Drawing Conclusions: Based on your calculations, is an inclined plane or a
pulley system more efficient? Explain your answer.
3.
Evaluating Methods: How would performing this experiment in a hands-on
laboratory affect your calculation of efficiency? What differences you might expect
doing these experiments with real-life machines that you are neglecting in a virtual
setting?
4.
Evaluating Hypotheses: How did your hypothesis compare to the results of
your experiments?
The lab report that you submit to your teacher should include:
1.
A document file (RTF) containing:
-Your experimental design idea and answers to the initial questions
-Your hypothesis about this experiment supported with physics concepts
-Conclusions from this experiment
2.
Copy the following spreadsheet information into your document:
-Data tables 1 and 2
-All of the tables you produced to do your calculations of mechanical advantage
and efficiency for the data collected in tables 1 and 2
Purchase answer to see full
attachment