THE PHYSICS LABORATORY

Name: Nanting Zheng

Date: 02/04/2014

Purpose: To learn to use the computer, interface, and a photogate sensor to conduct a scientific experiment that determines the velocity and distance of a falling object with respect to time. Students will be able to compare their data with theoretical values such as the force of gravity by performing multiple trials of the experiment to calculate the force.

Apparatus: A picket fence, photogate, Lab Pro, and the Logger pro Software.

Theory: A force may be thought as an influence that tends to change the motion of an object. One can easily find the theoretical value of force by multiplying the acceleration of gravity, ‘g’, which is 9.8 m/secˆ2 by the mass of the object. However, in this experiment, the student can only obtain a close estimate of the value for ‘g’ by finding the average of the slopes of the graphs and taking the standard deviation into consideration. The mass of the picket fence should also be reconsidered to eliminate as much error as possible. The error propagation formula below will assist in determining the value of F while taking any uncertainties into considered.

Where,

= Uncertainties associated with force

C= Calculated Force by multiplying g*m

= The smallest increment on the scale for measuring the picket fence

A= The mass of the picket fence

B= Standard deviation

B= The average value of g

Procedure:

1. Setup the photogate as shown below and connect the photogate into the input of the LabPro interface that is connected to a PC.

2. Open the file entitled ‘Lab #1 The Computer in the Laboratory’in the “Physics 1 Labs”folder.

3. Check to see if the photogate is working by either looking at the Gate State reading in the status bar at the top left of the screen or by checking the red indicator light of the photogate itself.

4. Click on Collect to start data recording. Hold picket fence perpendicularly to the photogate as shown above and release it from above.

5. Click Stop to end data recording and copy and paste velocity and time into Excel.

6. Repeat steps 4 and 5 for 5 more times and for the last trial, remember to copy the distance and time into excel.

Data and Calculations:

Table 1: The velocity of the picket fence with respect to time

Time (s)

Velocity (m/s)

0

0.014514

0.03592

1.559165

0.0473

0.065395

1.860421

0.074795

0.0904

2.133711

0.99195

0.112595

2.321932

0.120495

0.13354

2.522808

0.140796

0.152442

2.716307

0.159095

0.170402

0.176495

Graph 1: The velocity of the picket fence with respect to time

Table 2: The distance of the free fall respect to time

Time (s)

Distance (m)

0

0.014514

0.03592

0.05

0.0473

0.065395

0.1

0.074795

0.0904

0.15

0.099195

0.112595

0.2

0.120495

0.13354

0.25

0.140796

0.152442

0.3

0.159095

0.170402

0.35

0.176495

Graph 2: The distance of free fall vs time elapsed

Table 3: The acceleration values for trials

Trial No.

Slope

Accel. “g”

(m/secˆ2)

Average “g”

(m/sec ˆ2)

Standard deviation

1

9.9061

9.9061

9.7206

0.2651

2

9.5684

9.5684