act011

8/7/2019 act011

http://slidepdf.com/reader/full/act011 1/4

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, and your written record must be clear and neat enough for someone else toread.

C) Analysis is done after you have completed your observations. You will make your ownanalysis notes based on the analysis steps and questions in that day's activity instructions.Once you are satisfied that your analysis is correct, you will prepare a brief written report to

be handed in for grading.

D) The Exercise portion will follow the analysis and it will be similar to a homework problem.

E) Your Written Report is due at the end of the class. You should note at the top of the

page your name, section number, and activity number. The written report will includeyour data, analysis, and solution of the exercise. You are permitted to work with and obtainhelp from any source as you prepare your report – however, you may not directly copyanother person's report. Your written report should be succinct – usually two pages (frontand back of one sheet) will suffice. Handwritten reports are fine but must be legible.

F) Graphs are important in all three parts of the activity. All graphs in your written reportsshould 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 shapesof the lines and/or curves, values of minimum/maximum points, and any other features thatare important for understanding the data. You can ignore data taken before or after the timerange you are interested in. For example, if you are analyzing the motion of a cart, any datataken after you stop the cart with your hand are irrelevant.

Copyright©1999-2001 Cummings, Laws, Thornton, Sokoloff; Rev. Aug 09 RPI 1

8/7/2019 act011


Measuring the Position, Velocity, and Acceleration of a Cart on a Track

Push and release--keep handout of way of motion detector

We will be measuring the position, velocity, and acceleration of a cart on a track in the nextseveral 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 shouldalways be set on narrow beam using the small switch on the top. Note that even with thedetector 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 ). TheLabPro is connected to your laptop with a USB connector. The LabPro should be connectedbefore 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 avirtue. 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 report 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 atone and see some lights flash. Connect the USB cable to your laptop and wait for thewizard to complete (point D above). Start a LoggerPro session by clicking on theLoggerPro icon. Using the LoggerPro ‘File’ option, go to your Physics I folder (its defaultlocation is on the C dirve) and double-click on the file Kinematics.xmbl. Set up the motiondetector, 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. Givethe cart a gentle push away from the motion detector and let it go. Keep your fingers andhand on the end of the cart away from the motion detector so that the cart is always theclosest object to the detector. Catch the cart when it gets to the end of the track. The track isalmost frictionless and so the cart’s acceleration will be small, but the cart will slow downgradually due to friction. We will measure the effect of friction in a later activity. Whenyou 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 andthe start of data collection. When you hear the motion detector start to make a clickingnoise, give the cart a gentle push. Gentle pushes work better than hard pushes.

3) For Constant Velocity:a) Make measurements with LoggerPro as described above in Step 2.


8/7/2019 act011


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 0.2meters 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 upas it goes. Since the fan exerts a constant force on a constant mass, and we assume constantfriction and air resistance, the acceleration of the cart will be constant.

Fan UnitStart from rest

5) For Constant Acceleration:a) Make measurements with LoggerPro as described above in Figure 2. b) Draw graphs of displacement and velocity.

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 ExamineIcon ("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 portionof the graph shaded. Use the Integrate Icon to find the area under shaded part of thegraph.

e) Compare the displacement = (x2–x1) from 7.c with the integral from 7.d. Should theygive 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 betweent1 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 initialvelocity. Could you correctly predict whether the cart was speeding up or slowingdown? (Be careful here! You might want to come back to this question after doing theexercise.)


8/7/2019 act011


Documents

act011