PASCO ME-8930, Instruction Manual, Page: 19 / 40

012–06734A Smart Timer
15
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EQUIPMENT AND MATERIALS REQUIRED
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The purpose is to determine the acceleration due to the Earth’s gravity.
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The accepted value for the acceleration due to gravity on the Earth’s surface is 9.8 m/s
2
.
With the Smart Timer, the acceleration due to Earth’s gravity can be quickly determined
experimentally. The acceleration may be calculated from measurements of distance and
time, or it can be measured directly.
To calculate the acceleration from time measurements, the following formula must be used:
Note that
!
t is not t
2
, but is 1/2 t
2
(see Figure 1.1).
Figure 1.1
Explanation of why ½ t
2
is used in the formula for calcu-
lating g
V
1
V
2
Δ
t
Δ
t =
1 2 1 2
t
1
+
1 2 1 2
( t
2
– t
1
)
=
1 2 1 2
t
1
+
1 2 1 2
t
2
–
1 2 1 2
t
1
Δ
t =
1 2 1 2
t
2
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PART A—Determining the acceleration from time and
distance measurements
1. Mount the photogate on a stand, or hold the Photogate
steady so it is parallel to the floor, as shown in
Figure 1.2.
Figure 1.2
Experiment setup
Smart Timer
Picket Fence
Photogate
Picket Fence must
be dropped at a
90º angle.
To Smart Timer
channel 1 or 2
The 5 cm fence should
block the photogate
beam.
g =
Δ v
Δ t
=
v
2
– v
1
1 2 1 2 t
2
where
v
1
= 5cm
t
1
and v
2
= 5cm
t
2
– t
1