During this semester, you will use the Pasco 850 Universal interface connected to a computer and several software packages to collect and analyze data and present your results. Most of the time, when doing experiments, you will work as a team of two. Each team will have one Pasco 850 interface and a laptop computer to work with. All students are required to participate in all activities and stay until the session is dismissed.
Laboratory exercises are not just about getting the right result, but about recognizing that fundamental physics principles shape our everyday experiences and underlie many of the devices that we use in our personal and professional lives. Please do not treat the laboratories as cookbook exercises. Permit yourself to think! Thoughtful answers to the questions in blue will give you most of the laboratory credit.
Open a Microsoft Word document to keep a log of your experimental procedures and your results. This log will form the basis of your lab report. Address the points highlighted in blue.
Open a Microsoft Word document to keep a log of your experimental procedures and your results. This log will form the basis of your lab report. Address the points highlighted in blue.
Grading scheme for all labs:
25% for completion
In order to receive full
credit, you have to complete the entire lab and answer all parts.
Use full sentences explaining your results, show work, insert and properly label tables
and plots, proofread, and use correct units. Make comments if you are
stuck or if your results seem to have errors. Mention what could have
caused these errors in your results and how the results could be improved.
The reports are to help you, so use them like a journal to help
you think about the material.
25% for accuracy
You do have to put effort into
these labs. This is a 4 credit-hour course with lab, so, just like for
in-person labs, you have to set aside time to work on the labs.
50% for a reflection at the end of your report, i.e. a
personal account of your experience with the lab. It should be written
in the first person. You can format it as a report to a friend or
acquaintance.
You should reflect on the material and mention how well you understood
it.
Did you understand what you were doing during an exercise or activity, or did
you just follow instructions?
Do your results make sense to you, or do you expect them to be wrong? Why?
Do you have suggestions on how to improve the exercise or activities so students
can learn more from them?
...
Some of the phrases you may want to use are:
The most important thing was...
I learned that...
At the time I felt...
This was likely due to...
After thinking about it...
Later I realized...
This was because...
This was like...
I wonder what would happen if...
I'm still unsure about...
...
Today you will familiarize yourself with some of the software and hardware tools you will use in your studio sessions.
Equipment needed:Exercise 1
Your main tool for analyzing data will be the Microsoft Excel spreadsheet program. Let us go ahead and start using it.
Assume you have performed an experiment, measuring the position of an object moving along a straight-line path as a function of time. Your data are shown in the table below. You suspect that the object moved with constant speed, covering equal distance in equal time intervals. You want to verify this by producing a plot of position versus time and confirming that it is well-fitted by a straight line. If yes, then the slope of the straight line is equal the speed of the object in units of m/s.
Time (s) | Position (m) |
---|---|
0 | 0.00 |
1.5 | 2.64 |
3 | 5.22 |
4.5 | 7.61 |
6 | 10.22 |
7.5 | 12.84 |
9 | 15.43 |
10.5 | 17.98 |
12 | 20.52 |
13.5 | 23.03 |
15 | 25.37 |
Basic instructions for producing the plot are given below. Experiment with the various options Excel presents to you.
(a) Open Excel and enter your data.
(b) Produce a graph of position versus time.
(c) Study your graph. The plot of position versus time should resemble a straight line. The slope of the best fitting straight line should yield the average speed of the object. You can find this slope by adding a trendline to your graph.
(d) The fit is not perfect. The data you have collected contain experimental uncertainties. To find the resulting uncertainty in the slope you must use the regression function.
Note: The trendline is the best fitting straight line to the data.
It is the same line you get from the regression function line fit plot.
The slope of this trendline is your best estimate of the average speed.
The statistical uncertainty in the average speed is the standard error in the
slope you get from the regression function. This uncertainty only includes
the error due to the scatter in the data points, not any systematic error, such
as a calibration error.
Paste your labeled plot of position versus time (including the trendline) into your Word document and answer the questions below.
To practice entering and copying formulas, let us calculate the speed of the object for each small time interval from the raw data.
We want cell C2 to hold the speed of the object between t = 0 and t = 1 s. Speed is distance covered divided by the time interval. The distance covered is the difference between the entries in cells B3 and B2 and the time interval is the difference between the entries in cells A3 and A2.
Construct a plot of speed versus time. Let us use the a method that does not depend on the data occupying adjacent columns.
Paste your labeled plot of speed versus time into your Word document.
There is a huge scatter in the values, because of experimental uncertainties in the measurements of small distances and time intervals. But if we make many measurements we expect the average of these uncertainties to decrease with the number of measurements. (The fitting routine producing the trendline averages over all data points and therefore produces a speed value with a much smaller uncertainty.)
Let us find the average value of all entries in column C.
What is the value of the average speed? How does it compare to the slope of the straight-line fit?
Exercise 2
Sometimes the best way to measure the position of a moving object as a function of time is to make a video recording and then analyze the video clip. In this exercise, you will analyze a clip showing a cart moving on an air track. You will determine the position of the cart as a function of time by stepping through the video clip frame-by-frame and by reading the time and the position coordinates of the cart off each frame. You will construct a spreadsheet with columns for time and position, and a plot of position of the cart versus time.
To play the video clip or to step through it frame-by-frame click the "Begin" button. The "Video Analysis" web page will open. You can toggle between the current page and the "Video Analysis" page.
Paste your labeled plot of x(m) versus time (s) (including the trendline) into your Word document and answer the questions below.
Exercise 3
Use an on-line simulation from the University of Colorado PhET
group to explore vector addition.
Click
HERE to open the simulation.
Click the "Lab" image. Explore the interface
Use the simulation to solve the following problems:
(a) You walk 15.5 m in a direction 14.9o North of East.
Use the simulation to represent your displacement vector.
(b) To get to a restaurant, you leave home and drive 9
miles South and then 17 miles West.
Use the simulation to represent your displacement vector.
(c) Suppose you and a friend are test-driving a new car. You drive out of the car dealership and go 12 miles East, and then 5 miles South. Then, your friend drives 15 miles West, and 10 miles North.
(d) An airplane is flying North with a velocity of 200 m/s with respect to the air. A strong wind is blowing East at 30 m/s with respect to the ground.
In the studio sessions, you will also collect data using Pasco 850 interface and the Capstone software. The Pasco 850 interface is a data acquisition system connected to the computer. It can collect information from various analog and digital sensors, and generate seven different output signals. This exercise will familiarize you with this data acquisition system.
The instrument you will use today is the motion sensor. The motion sensor is a sonar ranging device. It uses pulses of ultrasound that reflect from an object to determine the position of the object. Our motion sensor cannot accurately measure distances smaller than approximately 20 cm.
You will use the motion sensor to measure the position of a mass oscillating on a spring as a function of time.
Pause the video when needed, so that you can follow the procedure step by step and learn about some of the capabilities of the data acquisition system.
Highlight your final graph in Capstone, click Edit,
Copy, and then paste it into your word document.
Do you think you are now familiar enough to acquire data with the motion sensor
without needing additional instructions? Please comment.
Convert your log into a lab report. See the grading scheme for all lab reports.
Name:
E-mail address:
Laboratory 1 Report
Save your Word document (your name_lab1.docx), go to Canvas, Assignments, Lab 1, and submit your document.