FREE FALL
OBJECTIVE
To measure the acceleration of a freely falling object.
INTRODUCTION
There is an old story that Galileo dropped similar spheres off the leaning
tower of Pisa to prove that objects do not, as reported by Aristotle, fall
with accelerations proportional to their masses. There is strong evidence
that Galileo never did the experiment as described in the story, but
gathered his data in an equivalent but much slower manner using inclined
planes. We will do the experiment as described in the traditional story but
using modern electronic timing equipment.
Galileo showed that an object falling freely in a uniform gravitational field
is constantly accelerated. The force that causes the acceleration is the
result of the mutual attraction between the falling mass and the earth. Of
course, if there are other forces present, such as friction or air resistance,
the motion of the falling object would not be one of constant acceleration.
However, if the distance of fall is not too great and the object is sufficiently
dense, the effects of air resistance are very small and may be ignored. If
we use Newton's second law to find the acceleration a of a mass m
subjected to a force F, we get
F
a =
(1)
m
If the force is the gravitational force, we call the acceleration g, the
acceleration due to gravity. This experiment is to study the motion of a
falling object in order to measure the acceleration g.
An object falling from rest with constant acceleration g for a time t will fall
a distance d given by
(2)
d = 1/2gt
2
It this experiment you will measure the height of fall d and the time t for
different heights and use the data to determine the value of g.
1