Lab Name:________________________________________ Partners:__________________________________________________________________________ Physics 170 Lab #2 MATERIALS: motion detector LabPro interface vernier calipers air track, blower and glider with "flag" riser blocks RESOURCES: Chapter 2 of the text (Giancoli) PRELIMINARY QUESTIONS: You must complete these preliminary questions before you begin collecting data. Make sure to have one of the T.A.'s (Brian or Alan on Tuesday, Luke or Mike on Wednesday) or Dr. Fischer initial your work before you begin collecting data. PRE-LAB GOALS: These questions are intended to get you thinking about position and velocity graphs. Question 2 will be particularly helpful in the lab when you study a glider moving with constant acceleration. 1. The velocity as a function of time of a toy car is shown in the graph below. Uniformly Accelerated Motion
b
.
t
.c .d
.
a
(a) When is the acceleration of the car positive, negative and zero? Explain your answer. You may refer to different regions according to the labels "a, b, c, d" on the graph.
(b) From the information in the graph, describe in a few sentences the motion of the car. Your description should include a discussion of the car's position, velocity and acceleration. You may
1
refer to different regions according to the labels "a, b, c, d" on the graph.
2. Let's say you observe the toy car rolling along in "one dimension" and you are told that the car is moving with a constant acceleration. (a) If the car starts out with zero velocity at t = 0, sketch a graph of the car's velocity as a function of time, assuming the car moves in the positive x-direction. Justify your graph in words and equations.
(b) How is the graph different if the car starts out with a non-zero velocity at t = 0? Explain.
2
(c) Sketch a graph of the car's position as a function of time if the car again has a constant acceleration. Justify your graph in words and equations.
Please read through the lab and give some thought to questions 2 and 3 in part 2. T.A. initials___________________ (You will receive no credit for these questions without these initials.) LABORATORY GOALS: There are two goals for this laboratory exercise. The first goal is to determine the acceleration of a glider on an air track for several different angles of incline of the track. The second goal is to obtain a value for the acceleration due to gravity. General procedure for collecting data for the glider on the air track 1. Turn on the air track and let the blower run for a couple of minutes. Place the glider on the track and check that the track is level. Make necessary adjustments to level the track, getting help from one of your T.A.s if necessary. 2. Place the "flag" on top of your glider, and place one of the riser blocks under a leg of the air track. You're going to use the motion detector to collect data for the motion of the glider. Position the motion detector at the higher end of the air track looking down at the flag on top of the glider. The figure below shows the general setup.
3
Setup for this experiment. The glider should be at least 40cm from the motion detector when you begin collecting data. 3. Now you're going to see if you can collect data, and if you've got the motion detector properly lined up with the flag on the glider. You can launch LoggerPro the same way you did in the first lab by going to the Physics Lab folder and opening the file "LabM1." Take a test run to see if the data collection is working properly, and make adjustments as necessary. 4. The experiment file "LabM1" shows distance and velocity versus time. LoggerPro has tools for performing some types of analysis, such as fitting curves (much like Graphical Analysis). To use these, you need to drag the mouse pointer across the region of the data that you want to look at. Then if you select the "Regression Line" tool, you can get information about a linear fit, or you can select the "Curve Fit" button and fit the data to a function of your choice. Try this out on your graphs. Part 1. Acceleration of the glider 1. Collect data for the distance and velocity of the as glider a function of time when there is 1 riser block under a leg of the air track. 2. Two of the equations of motion for constant acceleration are:
x = x 0 + v 0 t + 1 at 2 and v = v 0 + at . 2
Determine x0 , v0 , and a from the distance versus time graph, and v0 , a from the velocity versus time graph. Write the values you get below with the proper units, and explain how you have obtained these values. Attach a copy of the graph you used to find the values.
3. Remove the riser block from under the leg of the air track. Measure its thickness with the vernier calipers. Record the thickness of one riser below, giving units and an estimated uncertainty in your measurement.
4
4. We want to look at the relationship between the acceleration of the glider and the angle of incline of the air track. We are going to collect data systematically. The procedure will be to measure the thickness of the riser block(s), place the block(s) under the air track leg, perform 3 separate trials for each angle, and determine the acceleration of the glider from both the distance and velocity data for each trial. [Group] When you measure the thickness of the blocks, do you think it is better to measure the blocks individually or to measure them stacked together? Explain your reasoning.
5. Follow the procedure described above, and fill in the data table below, where h is the thickness of the riser block(s), and the "x vs. t" or "v vs. t" labels identify from which data set the value of a is obtained.
Number of blocks h (m) Trial 1 a (m/s2) from x vs. t 1 from v vs. t from x vs. t 2 from v vs. t from x vs. t 3 from v vs. t from x vs. t 4 from v vs. t from x vs. t 5 from v vs. t Trial 2 a (m/s2) Trial 3 a (m/s2) Avg (x vs. t) a (m/s2) Avg (v vs. t) a (m/s2)
5
Part 2. Determination of the acceleration due to gravity, g 1. [Group] Let's define the angle as the angle of incline of the air track, as shown below.
What should the acceleration of the glider be when = 0? Why do you say this? When = 90? Why do you say this? 2. The acceleration of the glider is the vector component of the acceleration due to gravity, g, that points in a direction parallel to the air track. We'll call this the x-direction. Using the picture below, determine an expression for ax in terms of g and . Explain your work clearly. Glider y-direction
ax x-direction g
3. How is h, the thickness of your riser blocks, related to the angle ? (HINT: The "best" way to do this is to use the distance between the l...