Background

Motion is an integral part of our daily activities. We rise from bed, take an early morning jog around the block, drive to school, walk to class, visit the library. All of these activities involve various kinds of motion. Pictures and graphs are useful ways to represent motion. The motion of a rolling tennis ball was frozen in the stroboscopic photograph shown above. The camera shutter was left open in a darkened room for 0.5 sec, while the film was exposed as the stroboscopic light flashed for a split second every 0.1 second. Which way was the ball rolling? How would you describe the motion of the tennis ball?

Purpose

1) To investigate horizontal motion.

2) To generate hypotheses for what can cause horizontal motion.

3) To create a model to predict the future and past positions of an object moving horizontally.

Materials

MacIntosh Computer	Motion Detector
Logger Pro Software	ULI box
Cart and track	styrofoam "reflectors"
batteries	battery slugs

Procedure

1) Choose 1-2 lab partners. Begin by setting the carts in motion carefully observing the carts move horizontally on the track. Practice pushing the carts to produce the most uniform motion you can. Discuss in your group what is meant by uniform motion.

2) While performing this experiment you should be reading through Experiment 0 to learn how to use the ULI, motion detector, and the Logger Pro software. Set up the experiment as outlined in the Procedure of Experiment 0.

3) Start your experiment by placing a cart on the track, pressing the Collect button on the Logger Pro window, and giving the cart a push down the track while the motion detector is clicking.

Did your graph look as you predicted it would? What should a distance vs. time graph of uniform motion look like? Repeat the experiment (several times if need be) and adjust the sampling rate, experiment length, and speed of the cart.

4) If time permits, analyze your plotted distance vs. time data by fitting a mathematical function to your graph using the Logger Pro software and following step 7 in the Procedure of Experiment 0.

5) Print out copies of the function-fitted graph for each member of your group. Indicate on your graph what mathematical function you used to fit your data (i.e. linear, quadratic, geometric, etc). (Note: Each student should turn in a separate Lab Report so be sure to print enough copies of the graphs for everyone in your group.)

Lab Report

Follow the Lab Report Guidelines (given in a separate hand-out) very carefully. Be sure to include all data collected in the experiment either in graph or table form. Be sure to describe the experiment accurately and according to the Lab Report Guidelines. Discuss the meaning of any graphs you obtained in terms of the objectives of the experiment. Be sure to label clearly any sketches, figures and graphs included in your report. As a help to get you started in writing your first lab report, some suggestions are listed below:

1) Describe what you did to produce a cart rolling on the track with uniform motion (constant speed).

2) Write down the mathematical function that describes the line that fits the data in any graphs you obtained. Express the equation using "significant digits" (i.e. does y=1.1846035 - 4.7823944x express the accuracy in the experiment well?) Be sure to describe all terms, and include units of measurement. Discuss the meaning of the slope of your distance vs. time graph. Give your interpretation of why your graph is a straight line (if it is).

3) Give your interpretation of any parts of your graph that deviate from a straight line. Make suggestions for the causes for such deviations from a straight line.