PASCO ME-9215B Photogate Timer - Manual (Page 31)

012-06379B Photogate Timer
27 ®
Teachers Guide
Notes - on Procedure, Experiment 1:
Instantaneous vs Average Velocity
f
In order to accurately measure D, allow D to the be the
distance between the points where the glider first trig-
gers the Photogate Timers.
i
If the Photogate Timer does not have a memory func-
tion, after the glider has passed through both
photogates, prevent it from triggering the Photogate
Timer again upon rebound.
Notes - on Analysis
Here are the results for the measurement of average ve-
locities with Photogate Timers positioned at seven differ-
ent distances apart.
Here is a plot of the average velocities of the glider being
measured by Photogate Timers positioned at seven differ-
ent distances apart. Answers - to Questions
c
The average velocity becomes a closer approximation
to the instantaneous velocity when the distance be-
tween the photogates is reduced.
d
Yes. The maximum error can be evaluated using the
standard deviation or best fit methods.
e
Timer accuracy has the greatest impact on the accu-
racy of velocity measurements. The ability to measure
small time intervals accurately will allow a better ap-
proximation of the instantaneous velocity. The object
being timed and type of motion should not influence
the accuracy of the measurements.
f
Instantaneous velocity is always inferred from an aver-
age velocity.
D t
1
t
2
t
3
t
4
t
5
t
avg
v
avg
(cm) (s) (s) (s) (s) (s) (s) (m/s)
80 1.85 1.85 1.85 1.86 1.86 1.85 0.43
70 1.61 1.61 1.61 1.61 1.62 1.61 0.43
60 1.37 1.38 1.38 1.37 1.38 1.38 0.44
50 1.13 1.14 1.14 1.13 1.14 1.14 0.44
40 0.90 0.90 0.91 0.90 0.90 0.90 0.44
30 0.68 0.68 0.68 0.68 0.68 0.68 0.44
20 0.45 0.45 0.45 0.45 0.45 0.45 0.45
Exp. 1 - Instantaneous Versus Average Velocity
Table 1.1
X
1
= 100.0 cm