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# Teachers Guide - Activity P06 Acceleration Due to Gravity

By Suzanne Mcdonald,2014-01-20 04:04
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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

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

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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