Course and Section_______ Names ___________________________

Date___________ _________________________________

One Dimensional Motion

Introduction

In the first part of this lab, we will be analyzing distance, velocity, and acceleration in one- dimension. We will be using a sonic motion sensor throughout this entire lab; so this first part is also to introduce you to this device and the supporting software.

The sonic motion sensor sends out pulses of sound that are at frequencies too high to be audible to humans. The pulses reflect off objects in their path, and the reflected pulses are returned to the sensor. The Pasco interface transmits the data to the Data Studio computer program, which can display and manipulate it. The computer records the time from which the pulse is first sent out until the pulse returns. The system can then calculate the distance to the object. The computer program is then able to determine the velocity and acceleration of the object.

The sensor cannot detect objects that are closer than 0.3m from the detector. The pulses also spread outward in a cone as they move away from the sensor, so make sure that the area in which you are working is as clear of obstacles as possible. The sensor is sensitive enough to detect small deviations in distance; therefore, an object with a flat reflecting surface may produce the best results.

EQUIPMENT: Sonic motion sensor, Pasco interface, Data Studio, meter stick.

A. Data Acquisition

PROCEDURE:

Open Data Studio and select Create Experiment. If Data Studio is unable to find the interface, make sure the power to the Pasco interface is turned on and the cables are connected (check with your instructor). Under Sensors, select and double click on Motion Sensor. The display should now show the motion sensor connected to the interface.

Close the Experiment Setup window and double click on Graph under Displays (lower left). A graph for plotting position versus time should appear. To start taking data with the motion sensor, click on the Start button at the top of the screen. To stop taking data, click Stop. Experiment with the motion sensor to get a sense of the size and range of objects that it can detect. Note that objects that are outside a certain cone of the ultrasonic beam cannot be detected.

B. Position Graphs

PROCEDURE:

The motion sensor should be plugged into the PASCO interface and ready to take data. You should notice how it is connected, for future reference. To start recording data, click on the "Start" button. Click on "Stop" to finish. Practice walking in the path of the sensor at a steady pace and/or standing still to create a position versus time graph.

Once a set of data is taken, you should see a graph of position vs. time. Click on the run of interest so that it is highlighted. If you would like to erase the data set, hit the delete key once the data set is highlighted. To the left you will also see various options for representing the data or choosing which data to look at.

1. Now see if you can create the following position graphs by walking in front of the sensor.

(a) Walk with constant velocity toward the sensor. Sketch here the resulting graph of position vs. time. How do you know the velocity was constant?

(b) Repeat (a), this time moving away from the sensor.

(c) Next you will be asked to try walking while accelerating toward the sensor. First, predict what the graph of position should look like. Then try it and describe the results.

(d) Try to reproduce the graph shown below. You may need to try this exercise a few times. Make a printout of the best graph. Describe the motion used to produce the graph on the printout of the graph you create. Note: In order to identify your graph, and perhaps add printed notes, click on the "Note" button. You will get a box within which you can write your name and any other identifying information you want to add. You can move the box around by clicking and dragging it.

Plot #1:

d(m)

t (s)

2. Looking at Plot #1, and using the relationship between distance and velocity, predict what the velocity versus time graph should look like. Make a sketch.

v(m/s)
		t (s)

3. You can display the velocity versus time graph by clicking on Velocity under the Data menu (upper left) and dragging it onto the position graph. Is this plot the same as you predicted? If not, then sketch the actual plot on the graph above using dotted lines.

C. Velocity Graphs

PROCEDURE

1. Now that DataStudio is set to produce velocity graphs, practice making velocity graphs by walking in front of the sensor as in the previous activity. First, delete the position graph by clicking on it and hitting the delete button. Then try to match the following velocity versus time curve. Make a printout of the best graph you create. On the printout of this curve, describe the motion used to produce the graph.

[Note: There are five sections to the graph. It would be a good idea to separate each section with a vertical dotted line. Label them I, II, III, … Then you could refer to each section when describing the motion.]

Plot #2:

v (m/s)		t (s)

2. How are positive and negative velocities defined?

3. Predict what the position versus time graph should look like for this situation and sketch it in the space provided.

x (m)
		t (s)

4. Now click and drag “Position” from the left-hand menu onto the velocity graph, to see

if your prediction was correct. If not, then sketch the actual plot above using dotted lines.

5. How can you tell from the velocity versus time plot that the object has changed direction?

6. Finally, let's look at an accelerating object. Predict what you think the graph will look like if you walk towards the sensor with a constant acceleration. Sketch your prediction below.

v(m/s)

t (s)

7. Now collect data by walking towards the sensor while speeding up. Does your graph look like your prediction?