Lab – Conceptual Graphing

Purpose

To make qualitative interpretations of motions from graphs.

Required Equipment/Supplies

TI 83+ with Physics application

Lab Pro or CBL2 ring stand

Motion detector large steel ball

calculator soup can

masking tape board

marker pendulum clamp

Discussion

In this lab you will hone your graphing skills. Using the motion detector you will try to match a randomly generated distance vs. time graph and a velocity vs. time graph. We will explore the graph of an accelerating object, and get our first look at harmonic or cyclical motion.

Procedure

Step 1 Using a motion detector, CBL and a calculator you will set up the graph matching

program as I will show you.

Step 2: Place the motion detector on a table so that its beam is chest high. Place three

strips of tape one meter, two meters and three meters, respectively, from the Motion Detector.

Step 3 Observe the random distance vs. time graph that you are given. Discuss with your

lab partners how someone would duplicate it. Sketch it in your lab book. The distance go from 0 to 3m in 0.5 m increments. When you are ready start timing and see if you can match the graph. Keep trying until it’s a good match.

Step 4 Repeat Step 3, but this time using a velocity vs. time graph.

Step 5. Set the motion detector at the top of a ramp that is at a 5-10 degree angle. Set it

to collect data as instructed by me. Place a soup can about 40 cm away. Start the motion detector and let the can go. When it is done collecting data, observe your distance vs. time and velocity vs time graphs. Sketch them in your notebook.

Step 6 Set up the ring stand and pendulum. Place the motion detector on a stack of books so it is at the same height as the pendulum bob. Pull the bob back at an angle of 20 degrees from the ringstand. Start the motion detector and then let the pendulum swing. When it has finished collecting data observe the distance vs time and velocity vs time graphs. Sketch them in your lab book.

Questions:

1. Explain in words how you moved to duplicate the two graphs that you sketched for parts 3 and 4. Did the graph move the way you predicted it would?

2. Why isn’t the distance vs time graph for the soup can a straight line? Was it moving with constant velocity? Constant acceleration? Explain.

3. How was the sketch of the pendulum different from the sketch of the can rolling down the ramp? We’ll come back to this later in the course, but why do you think that things that move like the pendulum are called “harmonic” (or cyclical) motion?

4. What does the slope of a distance vs. time graph tell us? What does the slope of a velocity vs. time graph tell us?