# 7.2: Introduction

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There is always some delay between the time an observation is made and the time it takes for a person to react and push the stop watch button, so the g-Ball will be used initially to remove the reaction time of a person from the process.  Objects falling in air all experience the same acceleration due to gravity, however, the air may affect these objects differently.  The average acceleration (a) of an object as it falls through air depends on the distance (d) it falls, and the time (t) it took for the object to fall.

$d = \dfrac {1}{2} at^2 \nonumber$