PASCO ME-9215B Photogate Timer - Manual (Page 9)

012-06379B Photogate Timer
5 ®
Experiment 1: Instantaneous Versus Average Velocity
x
0
1-2 cm support
x
1
Figure 1.1: Setting Up the Equipment
D
D/2 D/2
Card-
board D
Figure 1.2: Measuring Veloc-
ity in Gate Mode
EQUIPMENT NEEDED:
- Photogate Timer with Accessory Photogate
- Air Track System with one glider.
Introduction
An average velocity can be a useful value. If you know you will average 50 miles per
hour on a 200 mile trip, it’s easy to determine how long the trip will take. On the other
hand, the highway patrolman following you doesn’t care about your average speed over
200 miles. He wants to know how fast you’re driving at the instant his radar strikes your
car, so he can determine whether or not to give you a ticket. He wants to know your
instantaneous velocity. In this experiment you’ll investigate the relationship between
instantaneous and average velocities, and see how a series of average velocities can be
used to deduce an instantaneous velocity.
Procedure
c
Set up the air track as shown in
Figure 1.1, elevating one end of
the track with a 1-2 cm support.
d
Choose a point x
1
near the center
of the track. Measure the position
of x
1
on the air track metric scale,
and record this value in Table 1.1.
If you are using an air track with-
out a scale, use a meter stick to
measure the distance of x
1
from the edge of the upper end of the track.
e
Choose a starting point x
0
for the glider, near the upper end of the track. With a pencil,
carefully mark this spot on the air track so you can always start the glider from the
same point.
f
Place the Photogate Timer and Accessory Photogate at points equidistant from x
1
, as
shown in the figure. Record the distance between the photogates as D in Table 1.1.
g
Set the slide switch on the Photogate Timer to PULSE.
h
Press the RESET button.
i
Hold the glider steady at x
0
, then release it. Record time t
1
, the time
displayed after the glider has passed through both photogates.
j
Repeat steps 6 and 7 at least four more times, recording the times as t
2
through t
5
.
k
Now repeat steps 4 through 9, decreasing D by approximately 10 centi-
meters.
l
Continue decreasing D in 10 centimeter increments. At each value of D,
repeat steps 4 through 8.