Studio Physics I
Introduction to Motion in One Dimension
Here are a few comments to help you in all the lab work that you do in this course. Please
read these carefully.
A) Record all answers to questions on your own sheet of paper. Questions are clearly labeled,
“Question (A)” “Question (B)” etc.
B) “Sketch” means that you need to record the shape and most important characteristics of the
graph. You do not need numerical values. However, it should be clear where values are
zero, positive and negative.
C) When you record graphical data, you should always record ONLY the RELEVANT
DATA. You should not record any portion of the graph that corresponds to something that
happened before or after the period of time that interests you.
D) The motion detectors record the position, velocity and acceleration of WHATEVER object is
closest to it. This means that it will record your hand, book bag or whatever-rather than the
object that you want it to track-if you are not careful.
E) Do not try to detect objects that are closer than 0.5 meters from the detector. The motion
detectors go crazy and record complete nonsense.
F) Slow and/or gentle pushes and pulls almost always get you better data than fast and/or hard.
G) The carts and tracks that we use have reasonably low frictional forces between them. This
means that if you give a cart a good push, it will keep moving at a reasonably constant speed.
(It will not slow down much.)
H) Make sure your track is level. We have a carpenter’s level for this purpose.
I) You can hurt yourself with the fans. PLEASE BE VERY CAREFUL!!
LECTURE TAKE AWAY CONCEPTS:
1D Equations of Motion for Constant Acceleration
Basic Equations
1.
v  v 0  a t  t 0 
2.
x  x 0  v 0 ( t  t 0 )  12 a ( t  t 0 ) 2
Derived Equations
3.
x  x 0  12 ( v0  v)( t  t 0 )
4.
5.
x  x 0  v( t  t 0 )  12 a ( t  t 0 ) 2
v 2  v 02  2a x  x 0 
OBJECTIVES OF THE ACTIVITY:
1. Making sure LoggerPro is installed and working correctly on your laptop.
2. Understanding the basic operation of the motion detector, cart, and track. (We use these a lot.)
3. Learning general rules and guidelines that will apply to all Physics I activities.
4. Making and interpreting graphs of simple motion measurements in 1D.
Copyright©1999-2001 Cummings, Laws, Thornton, Sokoloff; Rev. 2003 Bedrosian, Borland
ACTIVITY: Position, Velocity, and Acceleration Graphs
1) You have a cart, a motion detector, and a fan. The system can be set up for constant velocity
(figure 1) or constant acceleration (figure 2).
Figure 1: Constant Velocity. Start the cart 0.5 meters away from the motion detector. Give
the cart a quick, hard push away from the motion detector and let it go. Catch the cart when
it gets to the end of the track. The track is essentially frictionless so no forces should act on
the cart, meaning acceleration is zero.
Push and release--keep hand
out of way of motion detector
Figure 2: Constant Acceleration. Mount the fan on the cart so that it is secure. Start the
cart 0.5 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, the
acceleration of the cart is constant.
Start from rest
Fan Unit
2) Open the software program “LoggerPro” (in the “Vernier Software” folder). You open the
file you will need for the first part of this activity by going File, Open, <Your Physics1
Data Folder>, L01A3-1 (Vel from Pos).mbl Set up the motion detector, track, and cart as
desired to answer the questions below. . Keep in mind that you have to keep your hand (and
everything else) positioned so that the cart is always the closest thing to the motion detector.
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 push.
3) For Constant Velocity (as in Figure 1):
a) What do your actual data look like for position versus time? Sketch a graph.
b) What do your actual data look like for velocity versus time? Sketch a graph. Make sure
that you include only relevant data in your sketch of the graph. [If you cannot get the
motion detector to make a clicking noise or you have any other problem taking data, go
back and check step #1. If you still cannot get it to work after 5 minutes or so, get help
from your instructor or a TA.]
c) Is your graph of position (x) versus time (t) linear or not?
d) Is x increasing, decreasing, or staying the same with time?
e) Is the slope of the line of x versus t constant or not?
f) What physical characteristic is described by the slope of the line of x vs t?
Copyright©1999-2001 Cummings, Laws, Thornton, Sokoloff; Rev. 2003 Bedrosian, Borland
g)
h)
i)
j)
Is your graph of velocity versus time increasing, decreasing, or staying the same?
What is the slope of your graph of v vs t?
What physical characteristic is described by the slope of the line of v vs t?
Sketch a graph of position versus time when you start the cart at the end of track farthest
from the detector and push the cart toward the detector.
k) Fill in the blanks: As the cart moves away from the detector, displacement is
__________(+ or –) and _____________ (increasing or decreasing). As the cart moves
toward the detector, displacement is __________(+ or –) and _____________ (increasing
or decreasing).
4) For Constant Acceleration (as in Figure 2):
You open the file you will need for the rest of the activity by going File, Open,, <Your Physics1
Data Folder>, L02A3-1 (Slowing Down).mbl You do not want to save your old file.
a) What do your actual data look like for velocity versus time? Sketch a graph.
b) What do your actual data look like for acceleration versus time? Sketch a graph.
c) What do your actual data look like for position versus time? You should sketch a graph.
You can display that graph by doing the following: Point your cursor to the word
acceleration on the y axis of the bottom graph and left click. You will get a check box
option menu. Remove the check from acceleration and add a check next to distance.
d) Is your graph of position versus time linear or not?
e) Is the slope of the line of x versus t constant or not?
f) What does your answer to “e” indicate about the velocity of the cart?
g) Is your graph of velocity versus time increasing, decreasing, or staying the same?
h) What is the slope of your graph of v vs t?
i) What does your answer to “h” indicate about the acceleration of the cart?
j) Sketch a graph of velocity versus time when you start the cart at the end of track farthest
from the detector and let the fan blow it toward the detector.
5) Slowing Down and Speeding Up:
Place the cart with the fan running at the end of the track farthest from the motion detector
and give it a gentle push toward the detector. The direction of the force from the fan should
oppose the initial motion, in other words push it away from the detector. Try to push just
hard enough so that the cart momentarily stops about 50-60 cm from the detector, then moves
back to the end of the track. Catch it before it falls off! Take data when you have practiced
this a few times.
a) Was the initial velocity of the cart (just after your push) positive or negative?
b) Was the final velocity of the cart (just before you caught it) positive or negative?
c) Did the cart’s acceleration change sign before and after the cart momentarily stopped, or
did the acceleration remain approximately constant with the same sign?
d) Is the cart slowing down or speeding up when the acceleration and velocity have opposite
signs (one positive and one negative)? (Slowing down means that the absolute value or
magnitude of velocity is getting smaller. Speeding up means that the absolute value or
magnitude of velocity is getting larger.)
e) Is the cart slowing down or speeding up when the acceleration and velocity have the same
signs (both positive or both negative)?
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. 2003 Bedrosian, Borland