# Question #f2b92

Oct 1, 2014

Your result for acceleration due to gravity, $\text{g}$, of ${\text{7.2m/s}}^{2}$ is incorrect. The kinematic formula that you should use to determine the acceleration due to gravity in this experiment is
$\text{d}$ = ${\text{v"_"i""t" + "1/2 gt}}^{2}$.
Since initial velocity is 0m/s, the equation becomes $\text{d}$ = ${\text{1/2gt}}^{2}$. Multiply both sides times 2, and you get
$\text{2d}$ = ${\text{gt}}^{2}$. Divide both sides by ${\text{t}}^{2}$, and you get ${\text{2d"/"t}}^{2}$. Plug in the values from your experiment, and you get
${\text{-2.64m"/"(0.43s)}}^{2}$ = -${\text{14.3m/s}}^{2}$.

You should get a value closer to -${\text{9.8m/s}}^{2}$. Did you measure the distance correctly? How many times did you drop the marble? Did you practice timing the drop before recording your data? Are your times consistent with one another? Is it possible that the marble was affected by air resistance?

I would recommend that you practice timing the drops until the times for the drops are consistent. (Important: Make sure the individuals doing the dropping and timing are at eye level with the top of the table or whatever you are dropping the marble from.) Then drop the marble three times for three trials to get an average for your time. If any of your times is way off from the others, throw out that one and repeat the drop.

I think the major issues are making sure the drop times are consistent by practicing first, before actually recording any data. If the time remains around .43s, and you are sure of your height measurement, then I would propose that air resistance is affecting the acceleration of the drop.