Description 1: Constant Velocity.
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.
Description 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.
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, Real Time Physics, Mechanics, Dual-Range
Force Sensor, 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?
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 physical characteristic is described by the slope
of the line of v Vs t?
j) 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,, Real Time Physics, Mechanics, Dual-Range
Force Sensor, 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)?
