Modeling Your Motion When Airborne

HPP A13v1

Modeling Your Motion When Airborne

Modeling Your Motion When Airborne

Review the Hints for Using Excel (Reference E) before coming to this lab.

Last lab you studied the motion of a person as they jumped straight up and down in the air. This lab you are going to expand this study to see what motion results when a person (like a diver) pushes off sideways at the same time as jumping up and becomes airborne. To help you with this investigation, you are also going to be introduced to two pieces of software that will simplify your analyses quite a lot. To get things started, you will first try out this new software to study the motion of a falling croquet ball.

Video of Falling Croquet Balls

Your instructor will show you videos of two falling croquet balls. Watch these videos carefully and discuss the following questions based on your observations.

In words describe the motion of the two balls in the videos. Let's refer to them as the "right croquet ball" and the "left croquet ball" so everyone can keep them straight. When you discuss the motion, be sure to identify to which ball you are referring.

Your instructor introduced the idea of frame rate. If a movie was filmed at a rate of 24 frames/s, then how much time passed between frames 3203 and 3217?

Qualitatively analyzing a movie of falling croquet balls

Start up the computer at your station and open the movie file named 1-Falling balls Movie. Watch the movie by pressing the play button. You can also step through the movie frame by frame by using the left and right arrow keys on the keyboard.

Relevant information: ? This movie was filmed at a rate of 625 frames/s, although some frames have been removed from this file so that only 5 remain. ? The croquet balls start at a height of 1.7 m above the floor. ? The initial frame (#00804) may not have been when the ball first started moving.

1. How much time has passed between the first two frames of this computer file? Explain.

2. (a) Compare the motion of the two balls in the vertical direction. That is, how do their up/down displacements compare during each of the frames?

(b) Compare the motion of the two balls in the horizontal direction. That is, how do their left/right displacements compare during each of the frames?

? Humanized Physics Project 2005 - UNL

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Modeling Your Motion When Airborne

(c) Based on your observations, how does the vertical component of velocity of the left croquet ball compared to that of the right croquet ball? What is your evidence?

(d) Based on your observations, how does the horizontal component of velocity of the left croquet ball compared to that of the right croquet ball? What is your evidence?

Invention Discussion #1 - Concepts of Projectile Motion

Quantitatively analyzing a movie of a falling croquet ball

Now that you have a feel for the motion of the croquet balls, you are going to use this movie to learn to use the new software tools. To get started, complete the following steps...

? "Quit" the software that displayed the movie file. ? Open the file 2-Falling balls.vpt. This should start up the software named VideoPoint. You

should be looking at the movie again as well as some software tools.

Data Collection

VideoPoint is software designed to help you analyze motion from videos. It has already been calibrated so it knows relative distances and the time between adjacent frames. You will now use this software to analyze in detail the motion of the left croquet ball (the one moving in both the x and y directions).

? Click on the "Collect Data" icon on the side bar.

? Carefully click on the location of the left croquet ball. Once you click, the software will automatically move you ahead to the next frame of the movie.

After you have clicked on the five positions, you can go back and adjust the position of your data if necessary. To do this, use the arrow keys to move to the frame where the adjustment is needed and use the arrows on the "Point Adjust" icon on the side bar.

Once you are satisfied with your five data points, then you should see the values of time, x-position, and y-position in the data table. Before you go any further, quickly record these values here (so you won't lose them in case you experience computer problems). This only needs to be recorded once per group.

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? Before you do anything else, save your work so you will not lose your data should there be computer problems. Select "Save As" from the "File" menu. Be sure to give the file a meaningful, appropriate name. Record the name of this VideoPoint file in your logbook.

? "Hide VideoPoint" using the Application menu in the uppermost right corner of the screen. Ask your instructor for assistance if this is unclear.

? Humanized Physics Project 2005 - UNL

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Modeling Your Motion When Airborne

Data Analysis The VideoPoint software should now be hidden. Start up the Excel file 3-Falling balls

Analysis.

Keep in mind that you can easily navigate back and forth between software programs by using the Application menu in the uppermost right corner of the screen.

Go back to the VideoPoint software using the Application menu. Bring the data table window to the front by selecting "Table" from the "Window" menu. Under the "Edit" menu, choose "Select All" to highlight the data and then select "Copy" from this same menu.

Hide VideoPoint again from under the Applications menu. Return to Excel. Click once on the cell A4 and select "Paste" from the "Edit" menu. Your data should now be in the spreadsheet. Ask your instructor for assistance if it did not work.

Before you do anything else, save your work so you will not lose your data should there be computer problems. Select "Save" from the "File" menu. Be sure to give the Excel file a meaningful, appropriate name. Record the name of this file in your logbook.

You can now use the power of Excel to create graphical and functional models of your data of displacement vs. time. You should start by creating models for x-component of displacement vs. time using the following procedures.

Graphical and Functional Model #1 - x-component of displacement vs. time

? Click once on the "Graph Wizard" button.

? Step 1 - Make sure to select XY (Scatter) for the chart type and the Chart sub-type with no connecting lines.

? Step 2 - Click on "Series" and then the "Add" button. Enter a short, but meaningful name for the data. Using your mouse, select all of the cells containing the x values (time) and the y values (x-position).

? Step 3 - Enter a name for the graphical model as well as a title for each axis.

? Step 4 - Select "Place object in Sheet 1" and then click on the "Finish" button.

You should now be looking at a graph of your data on the screen! Save the file again by clicking on "Save."

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Modeling Your Motion When Airborne

Your lab instructor can help you make adjustments to the graph as necessary. You should be sure it is in the correct format (titles, axes, units, etc.) just like all other graphs you have made in lab. In addition, you should check that the data points really appear to represent your data values. You have now created a graphical model of the x-component of displacement as a function of time for this croquet ball.

? Humanized Physics Project 2005 - UNL

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