Studio Physics I
Activity 01 — Introduction to Motion in One Dimension
General Instructions for Activities in Physics I
Here are a few comments to help you in all the activities that you will do in this course.
Please read these carefully.
A) Activities are divided into three parts:
● Observations – observing the general behavior of a system and collecting data,
● Analysis – making sense of the data with mathematics, and
● Exercise – a written homework problem based on the activity.
B) Observations must be done in class, with your active participation. You will record your
observations in a bound laboratory notebook. Your written record must be clear and neat
enough for someone else to read. You must bring your notebook to each class. A TA or
instructor will check that your observations are complete just before you leave. At that time,
you will sign an attendance sheet to verify that you participated in that class.
C) Analysis will begin in class and continue until the end of the period or you have completed
your analysis, in which case you should start on the Exercise. You will make your own
analysis notes in your laboratory notebook based on the analysis steps and questions in that
day's activity instructions. Complete the analysis at home if you run out of time. Once you
are satisfied that your analysis is correct, you will prepare a written report to be handed in for
grading at the beginning of the next class.
D) The Exercise portion will follow the analysis and it will be similar to a homework problem.
Again, work the problem out in your laboratory notebook first, and then copy it to be handed
in for grading at the beginning of the next class. You can do the exercise at home.
E) Your Written Report is due at the beginning of the next class. You should note at the top of
the page your name, section number, and activity number. The written report will include
your data, analysis, and solution of the exercise. You are permitted to work with and obtain
help from any source as you prepare your report – however, you may not directly copy
another person's report. Your written report should be succinct – usually two pages (front
and back of one sheet) will suffice. Handwritten reports are fine (if legible), but we will not
accept paper with ragged edges torn from a spiral notebook.
F) Graphs are important in all three parts of the activity. All graphs in your laboratory
notebook and in your written reports should have their axes clearly labeled with units and
scales. While you need not go into extraordinary detail when drawing your graphs, they
should clearly show the general shapes of the lines and/or curves, values of
minimum/maximum points, and any other features that are important for understanding the
data. You can ignore data taken before or after the time range you are interested in. For
example, if you are analyzing the motion of a cart, any data taken after you stop the cart with
your hand are irrelevant.
Copyright©1999-2001 Cummings, Laws, Thornton, Sokoloff; Rev. 02-Jan-07 Bedrosian
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Measuring the Position, Velocity, and Acceleration of a Cart on a Track
Push and release--keep hand
out of way of motion detector
We will be measuring the position, velocity, and acceleration of a cart on a track in the next
several activities. The points listed below will help you make more efficient progress with your
observations and take better data.
A) The "motion detectors" we use are actually ultrasonic position detectors. They should always
be set on narrow beam using the small switch on the top. Note that even with the detector on
narrow setting, any object close to the track will disturb the measurements. The track should
be located well away from any objects that could reflect sound pulses, including the electrical
outlets on the tables, your laptop computer, books, backpacks, etc.
B) The position reported by the motion detector is the distance from the detector, meaning that
velocity away from the detector (the arrow in the figure above) is the positive direction.
C) The motion detector does not work properly when the cart is closer than 20 cm (0.2 m).
D) The motion detector is connected to the LabPro device (on Digi-Sonic Channel 2). The
LabPro is connected to your laptop with a USB connector. The LabPro should be connected
before you start the LoggerPro software. When you connect the LabPro to your laptop for
the first time, the Windows "Found New Hardware" Wizard will run. Accept the defaults.
You must wait for the Wizard to complete before starting LoggerPro. Patience is a
virtue. If the Wizard does not complete in a few minutes, please get help.
E) Make sure your track is level. We have a carpenter’s level if you need it (just ask).
Observation Instructions
(Note each step in your laboratory notebook as you complete it, along with any data or graphs.)
1) Make sure the LabPro power is on by pressing the "setup" button on top. You should hear a
tone and see some lights flash. Connect the USB cable to your laptop and wait for the wizard
to complete (point D above). Go to your Physics I folder and double-click on the file
Kinematics.xmbl. This will start LoggerPro-3. Set up the motion detector, track, and cart as
needed to answer the questions below.
2) Nearly Constant Velocity. Start the cart 0.2 meters away from the motion detector. Give
the cart a gentle push away from the motion detector and let it go. Keep your fingers and
hand on the end of the cart away from the motion detector so that the cart is always the
closest object to the detector. Catch the cart when it gets to the end of the track. The track is
almost frictionless and so the cart’s acceleration will be small, but the cart will slow down
gradually due to friction. We will measure the effect of friction in a later activity. When you
feel that you are ready to collect actual data, set up the equipment and then click the “collect”
button at the top of the screen. There is a 1-2 second delay between doing this and the start
of data collection. When you hear the motion detector start to make a clicking noise,
give the cart a gentle push. Gentle pushes work better than hard pushes.
Copyright©1999-2001 Cummings, Laws, Thornton, Sokoloff; Rev. 02-Jan-07 Bedrosian
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3) For Constant Velocity:
a) Make measurements with LoggerPro as described above in Step 2.
b) Draw graphs of displacement (position) and velocity versus time.
4) Constant Acceleration. Mount the fan on the cart so that it is secure. Start the cart 0.2
meters away from the motion detector. Do not give the cart a push to get it moving. Rather,
turn on the fan and orient it so that the cart moves way from the motion detector speeding up
as it goes. Since the fan exerts a constant force on a constant mass, and we assume constant
friction and air resistance, the acceleration of the cart will be constant.
Start from rest
Fan Unit
5) For Constant Acceleration:
a) Make measurements with LoggerPro as described above in Figure 2.
b) Draw graphs of displacement and velocity.
At this point, if you have run out of time, save your data (by saving the LoggerPro file on your
laptop) so that you can work on the Analysis at home. If you have time, we expect your team to
start the Analysis in class, not leave early. You should try to finish the Analysis in class.
Analysis
6) For Constant Velocity:
a) Displacement is distance from the motion detector. Was it increasing or decreasing?
b) Velocity is the time derivative of displacement. Was it positive or negative?
c) How does your answer for (a) relate to your answer for (b)?
d) What would the graphs look like under ideal conditions with no friction?
7) For Constant Acceleration:
a) What would the graphs look like under ideal conditions with constant acceleration?
b) The cart should be speeding up. How can you tell from the velocity graph?
c) Pick two times, t1 and t2, between which the velocity graph looks like a straight line.
Use the mouse to locate the cursor over the position graph at t1 and use the Examine
Icon ("x=") to determine the value of position at t1. Call it x1. Similarly, get x2 at t2.
d) Again using the mouse, go to the velocity graph, click on the graph at t1 and hold the
button down, drag the mouse to t2, and release the button. You should see that portion of
the graph shaded. Use the Integrate Icon to find the area under shaded part of the graph.
e) Compare the displacement = (x2–x1) from 7.c with the integral from 7.d. Should they
give the same number within experimental error?
f) Use the Linear Fit Icon to find the best fit of a straight line to the velocity graph between
t1 and t2. The slope of that line will be acceleration. How does the numerical value of
slope for the line compare with the average acceleration = (v2–v1) / (t2–t1) ?
g) Suppose you had only an acceleration graph (ideal) but you did not know the initial
velocity. Could you correctly predict whether the cart was speeding up or slowing down?
(Be careful here! You might want to come back to this question after doing the exercise.)
Copyright©1999-2001 Cummings, Laws, Thornton, Sokoloff; Rev. 02-Jan-07 Bedrosian
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EXERCISE: Working with Position, Velocity, and Acceleration Graphs
In this exercise, you are given a graph of velocity of a cart versus time (shown below) and you
will need to calculate graphs of displacement and acceleration versus time. You will also be
asked to identify the time intervals during which the cart is speeding up and slowing down. You
can assume that the displacement = zero at time = zero.
v (m/s)
+1
t (sec)
0
2
4
6
8
10
-1
8) During what time interval(s), if any, is the cart speeding up? Slowing down? Hint: Try
sketching a graph of absolute value of velocity (speed) versus time.
9) Draw a graph of acceleration versus time. Your graph should include units and clearly show
the shape of the curve(s) that you draw.
10) Draw a graph of displacement versus time. Your graph should include units, clearly show the
shape of the curve(s) that you draw, and the value(s) at any minimum points, maximum
points, and points where the curvature changes. Hint: If you do your calculations using areas
instead of the formulas for one-dimensional motion, you will do the calculations faster and
with more likelihood of getting the correct answers.
11) What simple feature of the graph of velocity versus time tells you the time at which the cart
has the maximum displacement? Hint: Use physical reasoning in addition to math.
12) Compare the time intervals in which the cart is speeding up / slowing down with your graph
of acceleration versus time. Can you determine a relationship between acceleration and
velocity that reliably predicts whether the cart is speeding up or slowing down?
Important: You should have concluded that the cart is speeding up when acceleration and
velocity have the same sign, and slowing down when acceleration and velocity have opposite
signs. If you did not get that result, please check with your instructor or TA.
Copyright©1999-2001 Cummings, Laws, Thornton, Sokoloff; Rev. 02-Jan-07 Bedrosian
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