3
The default data-collection mode for Object Acceleration is Time-based. While
collecting data, accelerations and their associated time values are recorded. The
reported time value, referred to as the acceleration mid-time, is determined by
averaging the velocity mid-time values used for the acceleration value
calculation. You can make multiple acceleration measurements in the same data
set; however, it may be necessary to adjust the experiment duration in order to
collect your desired data.
Objects with more than two flags, such as a picket fence, will report
acceleration measurements for each successive pair of flags as the object passes
through the gate. It is not necessary to have one flag completely pass through
both gates before the subsequent flag enters the gate, such as happens when
using a Vernier Cart Picket Fence. Corresponding successive flag-velocity
measurements for the two internal gates are used when calculating accelerations
for multi-flagged objects.
For objects that have more than two flags, the average of the multiple
acceleration measurements can be used to represent the average acceleration of
the object.
Tips for using Object-Based Sensor Channels
l
To ensure you get accurate velocity and acceleration measurements, your
object should start outside the arms of the photogate and pass completely
through the gate without reversing the direction of motion partway through
the gate. When this is not followed, the reported data may not accurately
reflect the object’s motion.
l
We do not recommend using these sensor channels with pulleys, wheels, or
bar tape as these objects cannot be made to start completely outside the
gates.
l
Velocity measurements are only displayed when the second gate is blocked
within one second of the first gate being blocked.
l
Acceleration measurements require an object to have two or more “flags”
break the internal photogate beams while passing through the gate.
l
Accelerations are only displayed when, for each flag, the second gate is
blocked within one second of the first gate, and when the second flag blocks
its first gate within one second of the first flag unblocking its second gate.
l
Sensor meters for object-based sensor channels will update as objects pass
through the Go Direct Photogate; however, measurements are not stored in
the software unless you are actively collecting data.
l
The default data-collection mode for object-based sensor channels is Time-
based. No values are recorded for these sensor channels when using
Photogate Timing modes.
Gate-State Sensor Channels
Gate-State sensor channels report the same data that our traditional photogates
report. You can use these sensor channels along with object-based sensor data
collection to explore and verify velocity and acceleration calculations. The gate-
Object-based Sensor Channels
The object-based sensor channels are unique to Go Direct Photogate. These
sensor channels make use of the double-gate design for measurement of velocity
and acceleration. The object-based channel measurements do not depend on the
geometry of the object or its direction of motion through the gate.
Object Velocity
This channel is the default sensor channel of Go Direct Photogate. The channel
reports the velocity of an object as it passes through the arms of Go Direct
Photogate. This is similar to using a pair of traditional photogates in Pulse-
Timing mode.
Velocities are calculated by finding the time interval associated with the
successive blocking of the two internal gates. This time interval is referred to as
the pulse time. The ratio of the distance between the internal gates (2.0 cm) and
the pulse time is reported as the magnitude of the object’s velocity. An object
that first blocks Gate 1 then blocks Gate 2 will report positive velocities. An
object that first blocks Gate 2 then blocks Gate 1 will report negative velocities.
Velocity measurements can be displayed with units of m/s (default), cm/s, or ft/s.
The default data-collection mode for Object Velocity is Time-based. While
collecting data, velocities and their associated time values are recorded. The
reported time value, referred to as the velocity mid-time, is determined by
averaging the times used for the pulse-time calculation. You can make multiple
velocity measurements in the same data set; however, it may be necessary to
adjust the experiment duration in order to collect your desired data.
Objects with multiple flags, such as a picket fence, will report velocity
measurements for each flag as the object passes through the gate. It is not
necessary to have one flag completely pass through both gates before the
subsequent flag enters the gate, such as happens when using a Vernier Cart
Picket Fence. Corresponding blocked events for the two internal gates are used
when reporting velocities for multi-flagged objects.
For objects that have multiple flags, the average of the multiple velocity
measurements can be used to represent the average velocity of the object. The
slope of the best-fit line through the Velocity
vs.
Time data can be used to
calculate the average acceleration of the object as it passed through the gate.
Object Acceleration (multiple flags)
This sensor channel reports the acceleration of objects having two or more flags
that break the internal photogate beams while passing through the gate. This is
similar to using a pair of traditional photogates in Gate-and-Pulse-Timing mode.
Accelerations are calculated using velocity and velocity mid-time values
calculated for each flag as described in the Object Velocity section. The ratio of
the difference in successive flag velocity measurements and the difference in
their associated velocity mid-time values is reported as the object’s acceleration.
The acceleration values can be displayed with units of m/s
2
(default), cm/s
2
, or
ft/s
2
.