Objectives

• Analyze the motion of a student walking across the room.
• Predict, sketch, and test distance vs. time kinematics graphs.
• Predict, sketch, and test velocity vs. time kinematics graphs.

Introduction

One of the most effective methods of describing motion is to plot graphs of distance, velocity, and acceleration as a function of time. From such a graphical representation, it is possible to determine in what direction an object is going, how fast it is moving, how far it traveled, and whether it is speeding up or slowing down. In this experiment, you will use a Motion Detector to determine this information by plotting a real time graph of your motion as you move across the classroom.

The Motion Detector measures the time it takes for a high frequency sound pulse to travel from the detector to an object and back. Using this round-trip time and the speed of sound, you can determine the distance to the object; that is, its position. Logger Pro software will perform this calculation for you. It can then use the change in position to calculate the object’s velocity and acceleration. All of this information can be displayed either as a table or a graph. A qualitative analysis of the graphs of your motion will help you develop an understanding of the concepts of kinematics.

 

 

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Regarding the use of these web pages.
The text and general content of this lab experiment is largely the property of Vernier Software for use only by Capilano College Physics students.
Anyone else does not have the right to use these pages.

 

Prelab

1. Use a coordinate system with the origin at far left and positive distances increasing to the right. Sketch the distance vs. time graph (with time along x-axis) for each of the following situations:

• an object at rest
• an object moving in the positive direction with a constant speed
• an object moving in the negative direction with a constant speed
• an object that is accelerating in the positive direction, starting from rest

2. Sketch the velocity vs. time graph for each of the situations described above.

3. Print out the introduction for this experiment (the web page that has an introduction that starts with "One of the most effective methods of ..."). Then on the diagram in the introduction draw an arrow showing the direction of a positive velocity for the person walking. Be sure to write your name, student number and lab section on the printout.

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experiment setup

motion detector

Preliminary Experiments

1. Take notes how the motion detector has been setup and connected to the computer. The motion detector is connected to a Vernier LabPro interface which is connected into the computer serial or USB port. Specialized software ("Logger Pro") captures the data from sensors like the motion detector and presents the data values as well as graph views. The motion detector will detect even small object within a wide cone over a long distance but not reliably anything closer than about half a meter.

2. Aim the Motion Detector so that it points toward an open space.

3. Prepare the computer for data collection by selecting the 104 Logger Pro reference in the browser favorites. Then in the Logger Pro program select "File" and then "Open" and then "MotionDistance.mbl". This will load the motion experiment into the Logger Pro program for displaying distance and velocity with the motion detector. Notice what is being plotted on the graphs and the scaling being used.

4. With this program now, produce a graph of your motion when you walk away from the detector with constant velocity. To do this, stand about 1 m from the Motion Detector and have your lab partner click the collect button. Walk slowly away from the Motion Detector when you hear it begin to click.

5. Sketch what the distance vs. time graph will look like if you walk faster. Check your prediction with the Motion Detector.

6. Try to match the shape of the distance vs. time graphs that you sketched in the Pre-lab Questions section by walking in front of the Motion Detector.

Distance vs Time

Procedure

1. Click graph shown here to enlarged view and describe in words how you would walk to produce this target graph. Sketch/record the graph in your notes.

2. With the MotionDistance experiment loaded into Logger Pro, test your prediction by attempting to replicate the distance vs. time graph. Do this by positioning yourself in front of the motion detector and clicking the "collect" button. When you hear the Motion Detector begin to click, walk in such a way that the graph of your motion matches the target graph on the computer screen.

Hint: Sometimes it is easier to replicate a graph with movement of a book in front of the motion sensor instead of moving yourself. Just recognize the sensor will notice the first thing it sees and try to understand the motion needed to replicate the graph.

3. If you were not successful, repeat the process until your motion closely matches the graph on the screen. Sketch in your notes the graph of your best attempt.

4. Now attempt to replicate the second graph shown here.

5. Answer the analysis questions for this part next before proceeding to the Velocity/Time part.

 

Analysis

1. Describe how you walked for each of the graphs that you matched.
2. Explain the significance of the slope of a distance vs. time graph. Include a discussion of positive and negative slope.
3. What type of motion is occurring when the slope of a distance vs. time graph is zero?
4. What type of motion is occurring when the slope of a distance vs. time graph is constant?
5. What type of motion is occurring when the slope of a distance vs. time graph is changing? Test your answer to this question using the Motion Detector.

 

Velocity vs Time

Procedure

1. Click graph shown here to enlarged view and describe in words how you would walk to produce this velocity vs. time graph .

2. In Logger Pro, load the MotionVelocity experiment (File/Open/MotionVelocity) to test your prediction. Choose a starting position and stand at that point. Start the data collection by clicking "collect" button. When you hear the Motion Detector begin to click, walk in such a way that the graph of your motion matches the target graph on the screen. It will be more difficult to match the velocity graph than it was for the distance graph.

3. Now attempt to replicate the second graph shown here (click graph here for enlarged view).

Analysis

1. Describe how you walked for each of the graphs that you matched.
2. For each of you velocity vs. time graphs, sketch what you believe the distance vs. time graph would look like. Then in Logger Pro, and a distance vs. time graph to check your answer. Do this by double clicking on the y-axis label and checking Distance. Axis scaling can also be changed by clicking them.
3. What does the area under a velocity vs. time graph represent? Test your answer to this question using the Motion Detector.
4. What type of motion is occurring when the slope of a velocity vs. time graph is zero?
5. What type of motion is occurring when the slope of a velocity vs. time graph is not zero? Test your answer using the Motion Detector.

Further

1. Create a distance vs. time graph in front of the Motion Detector and sketch it into your notes. Now, in your notes, describe the motion involved with each part of the graph
2. Repeat the further step one but only now with the velocity vs. time graph.
3. Familiarize yourself with the software scaling of graphs. Try the zoom button to zoom into parts of the graph.
4. Familiarize yourself with other aspects of the software.