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The Electrifying

Acceleration of Gravity

Laboratory

 

Background Information:

            When an object falls through space acted on only by the force of gravity, it is said to be experiencing free fall.  Galileo Galilee was an Italian scientist, who in the 1600's experimented with falling objects.  Galileo found that all objects fall at the same rate. 

 

            Galileo's experiments showed that all falling objects on Earth experience the same acceleration due to gravity.  The acceleration of gravity (g) is 9.8 m/s2. (980 cm/s2)

 

Materials:

            electric timer                             500-g mass                              strip of paper               

            meter stick (ruler)                     carbon paper disc                     metal clip

            ladder                                       ring stand and clamp                 scotch tape

            piece of carpet to protect the floor                                           


Procedure:

 

            1.  Observe the instructor as the use of the Spark Timer is explained.

 

 

            2.  Obtain a strip of paper that has recorded the motion of the falling object.  Look at the dots on your strip of paper and note that the end attached to the mass has dots very close together.  Then the separation becomes greater and greater. 

 

                        . . . . . . .   .      .        .         .           .              .                .                           .

 

                        Beginning                                                                                                                             End

 

 

            3.  Fasten the strip of paper to your lab table using a piece of tape at each end.

 

 

            4.  Identify the beginning and end of the tape.     

 

 

                5.  Circle the first dot, and then circle every third dot afterwards.  Label these circled dots        as follows:  0 sec, 3/60 sec,  6/60 sec,  9/60 sec,  12/60 sec,  15/60 sec, etc.

 

 

                . . . . . . .   .      .        .         .           .              .                .                           .

 

            Beginning                                                                                                                             End

 

 

            6.  Measure the total displacement from the first dot (time zero) to each circled dot on your strip of paper.  Record these measurements in your data table.  Make sure to measure from the first dot each time.  DO NOT MEASURE THE DISTANCE BETWEEN THE DOTS!!

 

 

            7.  Calculate the change in position for each interval (0 to 3/60, 3/60 to 6/60, 6/60 to 9/60, etc.) by taking the final displacement minus the initial displacement for the interval.  (example:  d 2 minus d 1)  Record these values in your data table.  See your teacher for help.

 

 

            8.  Calculate the average velocity (v avg) for the interval by taking the change in position and dividing by the change in time (3/60 sec  = 0.05 sec) Record these values in your data table.

 

 

Graph:

 

            -Plot a graph of Average Velocity vs. Time using the data from the first and last columns of your data table. 

 

            Note:  You have calculated each velocity value at the mid-point of each time interval.  Therefore, your x coordinate should be halfway between the two times in column one.  (ex:  your first point should be half-way between 0 and 3/60 sec)

 

            -Make sure your graph has a title.

 

            -Draw the best-fit line (use a ruler) that passes as close to as many points as possible on your graph.  Note:  your line will NOT go through the point (0,0)

 

 

Analysis of Graph:                                                                                                                

           

            In your lab report, describe the

                        - shape of the graph

                        - relationship between time and average velocity

                        - points that were not included in your best-fit line (outliers)

 

 

Calculations:

 

           

            Slope

 

            1.  Draw two "nice" new points on your best-fit line, and find their (x,y) coordinates.  We will call these (x1,y1) and (x2, y2)

 

            2.  Calculate the slope of your line using the equation:

 

 

                                                (y2 - y1)

                        Slope = ____________________

                                                (x2 - x1)                       

 

 

            DON'T FORGET UNITS FOR YOUR SLOPE CALCULATION!!

 

            3.  The slope of your line represents the value for the acceleration of gravity of the falling object.

           

            4.  Calculate the class average for the acceleration of gravity.

Calculations continued:

 

            Experimental Error:

 

            Calculate your experimental error using the equation:

 

 

                        [your value for accel - accepted value for accel]

exp error = _____________________________________________                                                                            X 100  = _____ %

                                                accepted value for acceleration

 

           

            The accepted value for acceleration of gravity is 980 cm/s2.

 

 

                        Note:  Do all calculations in [  ] first.                                    

 

 

 

 

Questions:  Answer in complete sentences on the lab report sheet

 

1.  Why was air resistance not an important factor in this experiment?  Would the experiment be different if we used a different falling object, such as a feather?  Explain.

 

2.  What do you think the acceleration of gravity would be on the moon?  (guess a number)  Explain your answer.

 

3.  When Galileo was live, the world still did not know about electricity.  Obviously he could not have used an electric timer for his experiments.  Try to think of a way that Galileo could have conducted his work in the 1600's.