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Add a Low-Friction Pulley

The Ultra Pulley Accessory (order code SPA) connects to the photogate by using the

accessory rod that comes with the photogate. Place the rod though the hole in the

photogate and move the pulley into position so that the rod can be threaded into it.

Tighten up the rod so that the pulley is held firmly against the photogate. The Ultra

Pulley is a low-friction pulley with ten

spokes. The spokes break the photogate

beam so that the rotation of the pulley

can be monitored by the photogate. For

example, the motion of an Atwood’s

machine could be studied with an Ultra

Pulley and the Vernier Photogate.

Laser Pointer Stand

This light-weight tripod is a perfect

support for a laser pointer. The stand

features fold-out legs and a clip

attached to the adjustable ball. A socket head assembly securely holds the laser in

place. This assembly allows you to accurately point the laser at the photogate. A

VELCRO

strap integrated into one of the tripod legs allows you to attach the laser

to objects such as ring stands and railings.

Vernier Photogate and Early TI Publications

The Vernier Photogate should not be used as a replacement for the simple photogates

(using the TI light sensor) described in the CBL Experiment Workbook (which comes

with the CBL) or in Exploring Physics and Math with the CBL System. The

programs used with these books will not work with this type of photogate.

More Information on Geometric Aspects of Photogate Timing

Photogates have a number of geometric complications that result in the effective

length of an object passing through the gate being slightly less than the actual length.

Motion Timing

The Motion Timing mode uses a photogate or pulley connected to the digital input.

During operation, times are recorded as leading opaque edges of a “picket fence,”

bar tape, or a pulley spoke pass through the photogate beam. These times are

displayed in a data table. More importantly, if you enter the distance between the

leading edges of the opaque bands in the Length of Object field, the program can

analyze the times, and calculate velocities, displacements, and accelerations.

Pulse Timing

In this mode, a measurement from when a photogate gets blocked to when it gets

blocked again will be recorded.

Gate Timing

For this mode, timing will begin when the photogate is first blocked. The timing will

continue until the gate is unblocked. The duration of the interruption is thus timed. If

the length of the object is entered in the Length of Object field, the velocity is

calculated.

Pendulum Timing

the Pendulum Timing mode uses a photogate connected to an interface. The timing

will begin when the photogate is first interrupted. The timing will continue until the

photogate is interrupted twice more, so that you get the time for a complete swing of

a pendulum or other oscillating object.

Photogate Timing

In Photogate Timing mode, only a time and Gate State column are displayed. You

may add other calculated columns as desired.

For a good discussion of these issues, see Eugene P. Mosca and John P. Ertel,

“Photogates: An instrument evaluation,” Am. J. Phys. 57 (9), 840-844 (1989).

A more comprehensive tutorial can be found in the following documents:

 Logger Pro Introduction to the Vernier Photogate

http://vnr.st/xe80

 LabQuest Introduction to the Vernier Photogate

http://vnr.st/xe6f

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