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ICLE Standards:
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Physical Science: Develop an understanding of
forces and motions. Develop an understanding of energy and matter.
Science and Technology: Develop an understanding
about science and technology.
Mathematical Connections: Use and value the
connections between mathematics and other disciplines.
Functions: Represent and analyze relationships
using tables and formulae.
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Performance Task:
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Note to the teacher: For this activity, students
will need the following materials: mechanical support arm, small mass set,
S-hook, stopwatch, steel pulley, barrel pulley, meter stick, DC motor, power supply,
mechanical breadboard, masking tape, cord. It is best for students to work in groups of four.
For this activity, you will perform a laboratory experiment to determine
the effect of certain variables on the efficiency and operation of an electric motor. The task consists of two
parts. Part A gives procedures for you to set up the experiment, and Part B gives procedures for
collecting data in the experiment.
Part A: Setting Up The Experiment
- Using a set screw, secure barrel pulley (take-up drum) to the shaft of
the motor.
- Attach motor assembly to the mechanical breadboard.
- Using the S-hook, hang a single steel pulley to an eyelet on the
horizontal arm of the support stand.
- Align the support stand with the motor so that the axis of rotation of
both the motor/drum assembly and the pulley are parallel.
- Attach one end of the cord securely to the barrel pulley (take-up drum).
Feed the other end over the pulley. Attach it to a 50 g (0.05 kg) mass
hanger
- By hand, turn the drum/motor shaft until the cord is taut.
- Tape the meter stick in position to measure the height (h) the hanger
moves at a constant speed. The starting point should start after the hanger starts to move.
Use the
maximum distance the hanger moves before it reaches the pulley.
- Plug in the power supply.
- Connect the motor to the power supply.
Part B: Collecting Data
- One student operates the power supply unit, one student is the catcher
of the hanging masses, one student times the event, and another student records the data collected in
the Data Table (attached).
- Start collecting data while using the empty mass hanger only.
- Set the power supply for DC, turn the power adjustment knob to 0, and
turn the mode to volts.
- Turn on the power and slowly increase the voltage until the hanger moves
upward at a constant speed.
- Turn off the power switch without moving the adjustment knob.
- Reset the hanger in the starting position.
- Turn on the power and measure the time it takes the hanger to move from
the starting position to the end position. Turn off the power when the hanger reaches the end position.
At this time the hanger may fall, and the catcher is to make sure it is caught. Do this for three
trials, find the average of your three trials, and record in the Data Table.
- Reset the hanger in the starting position.
- Redo procedure #7, but this time change the mode to amps.
- Change jobs in your lab groups and redo data collecting procedures 3-9,
but add additional masses to the hanger. First add 50 g (0.05 kg) to the original mass, then 150 g (0.15
kg) to the original mass, and finally 350 g (0.35 kg) to the original mass.
- Perform the following calculations, putting your results in the Data
Table:
a. Weight (w) = mass (m) x acceleration due to gravity (a)
b. Work in (Wj) = volts (V) x current (I) x time (t)
c. Work out (Wo) = weight (w) x height (h)
d. % Efficiency = Work Out x 100%
Write up a laboratory report, giving a brief summary of your experiment and
stating any conclusions that you can make. Answer each of the following questions.
- Under what conditions would the motor efficiency be 100%?
- Is the motor an efficient method (>50%) to lift a mass?
- What happened to the voltage when the mass lifted was increased?
- What happened to the current when the mass lifted was increased?
- What happened to the percent efficiency when the mass lifted was
increased?
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Knowledge / Skills:
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Exhibit good data management skills by
collecting, organizing, and graphing data.
(s19)
Understand and apply the concepts of work and
power and how they relate to energy. An object experiences work when a
force displaces the object; power is the time-rate of doing work. (s19)
Follow written directions carefully and
accurately. (ela6)
Follow written directions carefully and accurately. (ela20)
Use writing as a tool for learning in formats
such as learning logs, laboratory reports, note-taking, and journals. (ela40)
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Rubric:
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4 Points =
The students complete the entire task without any assistance from
others. They work cooperatively to set up the experiment, indicating a
thorough understanding of the components necessary to establish a working
station. The students accurately and neatly collect the data and perform
all necessary computations. Their laboratory report is complete, correct, and
clearly written. There is a clear indication that the students have a good understanding of all major
concepts involved in the experiment.
3 Points = The students need some assistance from
others to complete the task. They work cooperatively to set up the
experiment, but have some difficulty setting it up. This is an indication
that they do not have a thorough understanding of the components necessary
to establish a working station. The students have some difficulty carrying
out the experiment, but finally complete their Data Table, which is fairly
accurate and well tabulated. Their laboratory report is complete, but lacks
clarity and conciseness in some of the written presentation. Students
appear to have an acceptable understanding of the major concepts involved
in the experiment.
2 Points = The students need much assistance from
others to complete the task. Although the students worked cooperatively,
they had difficulty collecting the data for analysis. Their data table was
not as neat nor as well organized as it could have been. The written laboratory report
is vague and hard to follow. The students demonstrate a lack of understanding of some of the
major concepts involved in the experiment.
1 Point = The students were unable to complete the task. They did not
set up a usable work station. Hence, it was not possible for them to
execute the experiment. They did make some attempt to collect data, but
those data were incomplete and inaccurate. The students were not able to
reach any meaningful conclusions. They demonstrated a lack of understanding
of most of the major concepts involved in the experiment.
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