2-Mar-2015 Free Fall Lab--determination of g and some statistics for analyzing data

The purpose of This lab is to examine the validity of the statement that in the absence of all other external forces except gravity, a falling body will accelerate at 9.8 m/s^2.

After professor has done the test with the equipment like picture 1.

(picture 1)

Professor gave us some series of dots on the paper corresponding to the position of the falling mass every 1/60^th of a second.(picture 2)

                                     (picture 2)

Place a two-meter stick next to the tape. Line up the 0-m mark with one of the dots and record the position of each dot as measured from the 0-cm mark. Then open Microsoft Excel and write down the data. (picture 3)

                                               (picture 3)

First cell  means time, I forget to enter TIME in cell A1.
X meas the distance between the dot and 0-m mark.
The third cell △x means the distance between the dot and next dot.
In cell D1, there is Mid-interval time (this gives the time for the middle of each 1/60^th second interval).
In the last cell, there is Mid-interval speed that comes from △x/(1/60).

we will have a line form the Mid-interval time/velocity graph(picture 4).
the equation is y = 9.60x + 0.69.

                                                                              (picture 4)
The slope is acceleration.  this acceleration 9.60 m/s^2 is our value of gravity.
After professor collected all of acceleration from other students in the class, we have a new data table(picture 5).

                                                                            (picture 5)

Then, we calculated a average g = 9.56 m/s^2.
The absolute difference is 9.56 - 9.8 = -0.24 m/s^2.
The relative difference is (absolute difference / 9.8)*100% = -2.45%

Different masses should have the same acceleration by freely falling-- gravity 9.8m/s^2. However, There were some errors. I think there was air friction. that is why we can not get the 9.8m/s^2.