Holding
a Constant Force
with a Finger
Experiments
from Team Labs
Experiment Profile
| Connections: | Physical Science, Physics, Biology, Physiology, Mathematics, Technology | |
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| Skills: | Graphing, Analyzing, Measuring, Inferring, Spread Sheet Formulas | |
| Math Concepts: | Difference, Sum of Difference, Absolute Value | |
| Duration: | 1 Class Period | |
| Team Size: | 2-3 students per group, or whole class demonstration | |
| Content Standards: | Science
Standard A (5-8)(9-12) Science Standard B (5-8)(9-12) Science Standard E (5-8)(9-12) Math Standard 1, 4, 5, 7, 9, 13 (5-8)(9-12) |
Summary
This finger force experiment is an excellent activity to introduce students to the basic measurement unit of force--the newton--and to develop their thinking and analysis skills. The activity is in itself very simple, but there are many opportunities for analysis, spread sheet skills and applied math to condense the data collected from the force probe into a more useful result.
To perform the experiment, have each student hold the force probe in their hand and try as best as they can to hold a constant force on the probe for the duration of one trial. Trials are typically thirty to sixty seconds in length using a sample rate of 100 samples per second. A typical value of force to use as a target is 20 newtons.
Several trials of holding a constant force are collected, from both the same student and other students. The analysis section of the activity comes from the comparisons of the results. It is very difficult to look at the raw data, either in graph form or tabular form, and determine which trial is actually the closest to the objective. By applying some simple math concepts and using the Excel spreadsheet, the student can reduce each trial to a single number. This number can be used as a "score", for easy comparison with other trials. There are several acceptable ways to produce this "score", and even more ways to compare the data statistically. This provides for a lively classroom discussion of methods and techniques and helps develop the problem-solving and thinking skills of the students. The Excel spread sheet is employed to perform the hundreds of calculations involved, demonstrating the power of the computer to analyze data.
Materials
- Host Computer
- ThinkStation SP16 Interface Kit
- ThinkStation Interface
- Power Supply
- Communications Cable
- Excelerator 2000 Software
- Force Probe with Table Adapter
Background
The muscles of the human body can be employed to perform many tasks. It is rare in nature that they are called upon to hold something steady. Try holding a small weight out at arm’s length for thirty seconds. This thirty seconds can seem like a very long time. Fine motor control is a learned skill, and a variety of feedback mechanisms are used by the brain to help control the muscles. The main feedback is usually visual, but the touch sensors of the body are also used. The level of control varies widely between students, with much variation observed between young students in the primary grades, and older students of high school age.
By employing the computer and the ThinkStation Probeware System, several additional feedback mechanisms become available. The subject can look at the graph as the data is collected, or look at the digital display of the force measurement. Students can discuss which feedback mechanism is the most effective.
The data can be analyzed in many ways. In this experiment, we will use a sum of difference technique. Using the spread sheet and the data in tabular format, each measurement of force is subtracted from the desired "target" value of 20 newtons. The result is the "error" of each measurement. These error values are then summed to create the score. Using this technique, a perfect score would be zero, with the increasing score indicating a trial that is farther away from the intended result. Students can compare their "scores" after several trials and determine the best approaches to holding a constant force.
The simple difference calculation for error does not create the desired result. A student with equal measurements above and below the desired target value would achieve a score of zero. The absolute value function must be used such that the error values are always positive. It is generally best to allow the students to discover this requirement on their own.
Other analysis techniques can be employed to examine this data. The students could compare averages, means, standard deviations or a variety of other statistical terms to compare results. The activity can be changed to a different objective, such as minimizing the standard deviation. Many possibilities for evaluation of the data exist, and each can be discussed in the classroom. This is the true objective of the Finger Force experiment.
Procedure
Collecting Data with the Force Probe
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1. Connect the ThinkStation Interface to your computer. Attach a force probe to one of the analog jacks on the front panel of the ThinkStation Interface. Snap the Table Adapter (flat surface) onto the end of the probe. Be sure to push it on hard enough that it snaps over the o-ring of the tip. A slight amount of lubrication (such as lip balm or petroleum jelly) can be used to make this easier. |
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2. Next, launch Excelerator 2000 and click on the Connect&GOTM icon. Excelerator will automatically identify the force probe and create a graph of force vs. time. The software also sets a default sample rate of 100 samples per second and default duration of 10 seconds. We will change the duration to thirty seconds using the Experiment Clock dialog. |
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3. To change the duration of the experiment, click on the Edit Clock icon located on the right side of the Excelerator toolbar. |
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Set the duration to 30 seconds. |
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4. Click on Window in your menu items and select the Digital Display to display the force probe readings in a digital format. Arrange the windows with the digital display at the top and the force graph across the bottom. |
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5. At this point, you are ready to record some data. Hold the force probe in one hand with either the index finger or thumb on the tip of the probe. The Table Adapter provides a larger surface area for the finger to contact the probe. |
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Click the green GO button on the left side of the Excelerator toolbar. |
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6. Excelerator will record the force being applied to the probe for the duration of 30 seconds and will display a graph similar to the one shown here. |
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7. Practice and record as many trials as desired. When the subject is ready for their best run, have them hold the desired force and click the GO button. Record the entire trial. When complete, save the trial by clicking on the Save Trial button on the toolbar. |
Analysis of the Data
| 1. Try to compare the results from several trials. It is difficult to determine how well you achieved your goal of holding the constant force. A numerical method of analyzing the data must be developed. | |
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2. Click on the Excel window to activate Excel. Select the trial of interest. Trials are saved by number, such as "trial 1", "trial 2", etc. You can double click on the sheet tab at the bottom of the Excel screen to rename the trial using the subject’s name, if desired. The trial should appear similar to the one shown here. |
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3. Beginning in cell D6, enter the formula:
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| 4. Fill the formula down adjacent to all of the measurements on the sheet. The formula can simply be "dragged" down the column to accomplish this. TIP- you can also double click the lower right corner of the cell containing the formula. Excel will copy the formula down for any cell that has data in the cell to the left. This is a very handy trick to know! | |
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5. This column represents the error in the measurement from the desired force value of 20 newtons (be sure to label the column with a heading and units). Note that the error is both positive and negative. |
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6. Next, compute the absolute value of the error. In cell E6, enter the formula below and fill down adjacent to all of the measurements.
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The result is an error table that contains only positive values. |
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7. Now it is time to actually compute the score. The score is simply the sum of the absolute value of the difference. In cell F6, enter the formula:
Note that this can also be done by entering =sum( and then using the mouse to select the data you wish to sum. |
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8. The result is the desired score as shown here. You may want to apply some formatting to the cell such as boldface type or various colors to make the result stand out. It is also good to discuss the number of significant figures used to display the data. How much “precision” is required, or desirable? |
Assessment
To confirm the students understanding of the analysis techniques employed, ask them to discuss other approaches to calculating the score. Discuss the merits and shortfalls of any alternative approaches. For example, the students could use the Mean and Standard Deviation function available in Excel to examine the data, and compare results using these metrics.
How could the absolute value of the error be computed if Excel did not provide an absolute value function? How was it done in the "old" days? Does the square root of the sum of the squares provide the same result? Can the square and square root functions be employed to achieve the absolute value of a number?
Extensions
- What factors make holding a constant force easier or more difficult?
- What happens if someone is talking to the subject while they are running a trial? Does that affect their concentration?
- Can this activity be used as a lie detector?
- Which feedback mechanisms provide the best results, and is it the same for each student?
- How much does practice affect the outcome? Can people actually learn to do this better?
- Taken as a statistical group, who is better at holding a constant force -- boys or girls?
- Does the target force affect a subject’s ability to hold the force constant? Should the target force be scaled by one’s body weight or age?
This activity will produce the opportunity for a variety of classroom discussions. The objective is to engage your students’ thinking processes and help them develop problem-solving skills while employing the tools of technology. Can you imagine doing this activity without a probeware system and a computer? It would be very tedious and time consuming.
We at Team Labs would be very interested in any classroom applications of this activity or feedback you wish to provide. Please send any questions or comments to webmaster@teamlabs.com.
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About the author... John Staarmann is the President and Chief Scientist at Team Labs. He is the designer and developer of the Force Probe. |
If you have a great experiment idea, please send mail to the WebMaster. |
Download a PDF of this experiment
(65 KB)
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