Gravitational Acceleration
A special case of constant acceleration is free fall (falling in vacuum). In problems of free fall,
the direction of free fall is defined along the yaxis, and the positive position along the yaxis
corresponds to upward motion. The acceleration due to gravity (g) equals 9.8 m/s
2
(along the
negative yaxis). The equations of motion for free fall are very similar to those discussed
previously for constant acceleration:
where y
0
and v
0
are the position and the velocity of the object at time t = 0.
Example
A pitcher tosses a baseball straight up, with an initial speed of 25 m/s. (a) How long does it take
to reach its highest point ? (b) How high does the ball rise above its release point ? (c) How long
will it take for the ball to reach a point 25 m above its release point.
Figure 2.4. Vertical position of baseball as function of time.
a) Our starting points are the equations of motion:
The initial conditions are:
* v(t = 0) = v
0
= 25 m/s (upwards movement)
* y(t = 0) = y
0
= 0 m (Note: origin defined as position of ball at t = 0)
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 Fall '09
 Acceleration, ball, Highest point

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