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Teachers Guide - Activity P06 Acceleration Due to Gravity

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Teachers Guide - Activity P06 Acceleration Due to Gravity

Name _____________________ Class ______________ Date _________

    Activity P06: Acceleration Due to Gravity

    (Motion Sensor)

Concept DataStudio ScienceWorkshop ScienceWorkshop (Win)

    (Mac)

    Linear motion P06 Gravity.ds G14 Gravity G14_GRAV.SWS

Equipment Needed Qty Other Qty

    2 Ball, rubber 1 Motion Sensor (CI-6742)

    1 Level (optional) 1 Base and Support Rod (ME-9355)

    Meter stick 1

    What Do You Think?

    How can a Motion Sensor be used to measure the acceleration due to gravity of a falling object?

    Take time to answer the ‘What Do You Think?’ question(s) in the Lab Report section.

    Background

    Over twenty-two centuries ago, a Greek philosopher and scientist named

    Aristotle proposed that there is a natural force that causes heavy objects to fall

    toward the center of Earth. He called this force “gravity”. In the seventeenth

    century, the English scientist Isaac Newton was able to show that gravity is a

    universal force that extends beyond Earth. It is the force that causes the moon

    to orbit the Earth and the Earth to orbit the Sun.

    When an object is in “free fall”, it means that the only force acting on it is the

    force of gravity. As an object falls freely, it accelerates. For a falling object near

    the surface of Earth, the rate of change of velocity is a constant value. This

    value is the acceleration due to gravity. If you ignore air resistance, a falling ball

    accelerates as if it is in free fall. You can measure the motion of the falling ball

    to find the value of the acceleration due to gravity.

SAFETY REMINDER.

     Follow directions for using the equipment.

For You To Do

    Use the Motion Sensor to measure the motion of a ball as it falls and bounces. Use DataStudio or

    ScienceWorkshop to record and display the position and velocity of the ball. Examine the slope of

    the line on a velocity versus time graph to find the acceleration of the ball.

    P06 ? 1999 PASCO scientific p. 35

Physics Labs with Computers, Vol. 1 Student Workbook

    P06: Acceleration Due to Gravity 012-07000A

    About the Motion Sensor

    The Motion Sensor sends out pulses of PULSE

    ultrasound and picks up the echoes of

    ECHOultrasound that bounce back from objects in

    front of it. OBJECT

    The software program keeps track of the

    time when the pulses go out and the time

    when the echoes come back. One-half of the MOTION SENSORround trip time is the time that it took for the

    ultrasound to reach the object. Since

    ultrasound travels at the speed of sound, or about 344 meters per second (or about 700 miles per

    hour), the program figures out how far away the object is as follows:

    roundtrip time distance to objectspeed of sound2The speed of sound through air depends on several factors, including the temperature of the air.

    Because the temperature of air can change, the speed of sound can change. You can calibrate the

    Motion Sensor so it uses an accurate measurement of

    the speed of sound.

    PART I: Computer Setup

    1. Connect the ScienceWorkshop interface to the

    computer, turn on the interface, and turn on the

    computer.

    2. Plug the modular connector on one end of the

    interface cable into the side of the Motion Sensor.

    Connect the stereo phone plugs of the Motion Sensor to Digital Channels 1 and 2 on the

    interface. Connect the yellow plug to Digital Channel 1 and the other plug to Digital

    Channel 2.

    3. Open the file titled as shown:

    DataStudio ScienceWorkshop (Mac) ScienceWorkshop (Win)

    P06 Gravity.ds G14 Gravity G14_GRAV.SWS

     The DataStudio document has a Workbook display. Read the instructions in the Workbook.

     The ScienceWorkshop document has a Graph display of Position and Velocity versus Time.

     The Trigger Rate for the Motion Sensor is 60 times per second (60 Hz).

    p. 36 ? 1999 PASCO scientific P06

Name _____________________ Class ______________ Date _________

PART II: Sensor Calibration and Equipment Setup

    Sensor Calibration

     Calibrate the Motion Sensor so it can use an accurate

    measurement of the speed of sound in air. You will need a

    meter stick and a flat surface that can be used as a target to

    reflect the pulses from the Motion Sensor.

    Set Up the Sensor

    1. Place the Motion Sensor so it is exactly one meter away

    from a flat surface that can reflect the pulses from the

    Motion Sensor.

     For example, put the Motion Sensor on a support rod near

    the edge of a table. Aim the Motion Sensor so it sends

    pulses down to the floor. If the floor has a rug or carpet on

    it, put a flat, smooth piece of wood or some other flat

    surface on the floor directly below the Motion Sensor.

    (• NOTE: Remove the meter stick after you use it to measure

    the distance from the Motion Sensor to the reflector.)

    Calibrate the Software

    2. In the Experiment Setup window, double-click the sensor‟s icon.

     Result: In DataStudio, the Sensor Properties window opens.

    Click the „Motion Sensor‟ tab. Result: The calibration window opens and the sensor begins

    to click a few times per second.

    P06 ? 1999 PASCO scientific p. 37

Physics Labs with Computers, Vol. 1 Student Workbook

    P06: Acceleration Due to Gravity 012-07000A

     Result: In ScienceWorkshop, the sensor‟s calibration window opens and the sensor begins

    to click a few times per second.

    p. 38 ? 1999 PASCO scientific P06

Name _____________________ Class ______________ Date _________

3. Calibrate the software.

     First, make sure that the sensor is one meter from the target.

     Second, click the „Calibrate‟ button in the Motion Sensor window. Result: The software

    calculates the speed of sound based on the calibration distance (one meter) and the round

    trip time of the pulse and echo

    4. Click „OK‟ to return to the Experiment Setup

    window.

    Equipment Setup

     Make sure that the floor is level. If it is not, put a

    hard flat surface on the floor and put pieces of

    paper or shims under the edges of the hard flat

    surface to level it.

    1. Put a base and support rod near the edge of a table.

    Mount the Motion Sensor on the support rod so

    the Motion Sensor is aimed downward at the floor. 2. Adjust the position of the Motion Sensor on the

    support rod so that there is about 1.5 meters

    between the Motion Sensor and the floor.

    PART III: Data Recording

    1. Prepare to drop the ball so it falls straight down

    beneath the Motion Sensor. Hold the ball between

    your finger and thumb under the Motion Sensor no

    closer than 15 cm (about 6 inches) below the

    Motion Sensor.

    2. Start recording data. (Hint: In DataStudio, click „Start‟. In ScienceWorkshop, click „REC‟.)

    Drop the ball. Let the ball bounce several times. NOTE: Be sure to move your hand out of the way as soon as you release the ball.

    3. After the ball bounces several times on the floor, stop recording data.

    P06 ? 1999 PASCO scientific p. 39

Physics Labs with Computers, Vol. 1 Student Workbook

    P06: Acceleration Due to Gravity 012-07000A

    Analyzing the Data

     The position plot of the Graph shows a “mirror image” of a ball bouncing on a flat surface.

    The velocity plot shows a “sawtooth” pattern. Notice in the velocity plot that the velocity of

    the ball is positive part of the time and negative part of the time. The Motion Sensor records

    motion away from it as positive and motion towards it as negative.

    1. In the plot of Velocity versus Time, use the cursor to click-and-draw a rectangle around a

    region that is relatively straight.

    2. Use the Graph display‟s built-in analysis tools to determine the slope of the region you

    selected.

     Hint: In DataStudio, select „Linear‟ from the „Fit‟ menu (). Hint: In ScienceWorkshop, click the „Statistics‟ button () to open the statistics area.

    Select „Curve Fit, Linear Fit‟ from the „Statistics Menu‟ (). p. 40 ? 1999 PASCO scientific P06

Name _____________________ Class ______________ Date _________

3. Record the value of the slope in the Data Table. This is the value for the acceleration due to

    gravity on the falling object.

     Hint: In DataStudio, the slope appears in the „Fit‟ window. Hint: In ScienceWorkshop, the Statistics area shows the general formula for a line (y = a1 +

    a2 x), the constant a1, and the linear coefficient a2. The linear coefficient is the slope of the

    line.

    Record your results in the Lab Report section.

    P06 ? 1999 PASCO scientific p. 41

Physics Labs with Computers, Vol. 1 Student Workbook

    P06: Acceleration Due to Gravity 012-07000A

    Lab Report - Activity P06: Acceleration Due to Gravity

    What Do You Think?

    How can a Motion Sensor be used to measure the acceleration due to gravity of a falling object?

Data Table

    ‘g’ (slope of velocity versus time) = _________ Questions

    1. How does your value for „g‟ (slope of velocity versus time) compare to the accepted value

    2of the acceleration of a free falling object (9.8 m/s)?

    accepted value-experimental value Reminder: percent difference = x100% accepted value

2. What factors do you think may cause the experimental value to be different from the

    accepted value?

    p. 42 ? 1999 PASCO scientific P06

Name _____________________ Class ______________ Date _________

P06 ? 1999 PASCO scientific p. 43

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