PASCO
 
MAIN PROCEDURE
In this experiment, students will use a motion sensor to discover the concepts of relative motion and frames of reference.
    1. The cart with the motion sensor is the observer. Hold it motionless for the first data run.
    2. Click Start and push the cart without the motion sensor gently toward the observer. Data collection will automatically stop when the carts are 40 cm apart. Catch the carts before they collide!
    3. For the next data run, click Start then gently push the two carts toward one another. Try to give them both about the same speed as the moving cart in the 1st data collection run. Data collection will automatically stop when the carts are 40 cm apart. Catch the carts before they collide!
    4. For the final data run, place the observer (motion sensor) at one end of the track and the other cart 50 cm away.
    5. Click Start, then gently push the two carts in the same direction both with about the same speed as in the first two data collection runs. Data collection will automatically stop when the carts are 40 cm apart. Catch the carts before they reach the end of the track!
    6. You should have a total of three data runs.
    1. In general, what pattern do you notice between the slope of the position-time graph and the velocity you found from the velocity-time graph?
    2. Looking at the velocities for the three different data runs, how do they roughly compare?
    3. How do you explain these very different velocities, even though you tried to push the carts with about the same speed in each data run?
    4. Specifically, how does the motion of the observer (motion sensor) affect the measured velocity?
    5. Is it possible for an observer to measure a velocity of zero for an object that is moving? Explain.
    6. Is it possible for an observer to measure a non-zero velocity for an object that is motionless? Explain.
    7. Scientists call the location of the observer relative to the object of interest the frame of reference. Why do you think they chose this name?
    8. Thinking of a speedometer in a car, it measures the car’s speed relative to what? How do you know?