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10
Photogate Timer
012-06379B
®
g
Set the Photogate Timer to GATE mode. Now move the ball to a starting point somewhere
on the ramp. Mark this starting position with a pencil so you will be able to repeat the run,
starting the ball each time from the same point. Hold the ball at this position using a ruler or
block of wood. Press the RESET button. Release the ball so that it moves along the ramp
and through the photogate. Record the time in Table 3.1.
h
Repeat the trial at least four more times with the same starting point, and record your times in
the table.
i
Measure the distance from the point directly below the ramp to each of the landing spots of
your ball. Record these distances in the data table.
Data and Calculations
c
Take the average of your measured times and of your measured distances. Record these aver-
ages in the data table. Also record the average distance as
d
x
in the space provided to the right
of the table.
Table 3.1
Data from Photogate Timer
Trial
Time
Distance
1
2
3
4
5
Averages
v
0
(avg)
Δ
Δ
Δ
Δ
Δ
d
=
Vertical height,
d
y
=
Average horizontal distance,
d
x
=
Horizontal velocity,
v
0
=
Percentage difference =
d
Divide
Δ
Δ
Δ
Δ
Δ
d
by your average time to determine
v
0
,
the velocity of the ball just before it left the
table.
e
Now determine the horizontal velocity of the sphere using the equations for projectile motion
and your measured values for
d
x
and
d
y
:
d
x
= v
0
t; d
y
= 1/2 at
2
;
where
a
equals the acceleration caused by gravity (9.8 m/s
2
or 980 cm/s
2
).
f
Compare your two values for
v
0
. Report the two values and the percentage difference.
Optional
If you have time, choose a value for
d
x
and a value for
d
y
. For what value of
v
0
will the ball
travel the distance
d
x
as it falls the distance
d
y
? Adjust the height and angle of the ramp and the
starting point until you produce the predicted value of
v
0
. Now run the experiment to see if
your calculated values for
d
x
and
d
y
are correct.