Vernier Software and Technology
Vernier Software & Technology
Tech Info Library

Should I use a photogate or a Motion Detector?

Motion Detectors and photogates can both measure motion, but both have advantages for certain experiments.

Photogate, order code VPG-BTD, $49
Photogates are sometimes capable of higher accuracy and function more like a spark timer in that the only information collected is the time at which a specific event occurred. Because of the sparse amount of data, students need to have a deeper understanding of the math behind an event in order to analyze the data. The age and ability of the student determines whether this is a pedagogical advantage or a disadvantage.

Motion Detector, order code MD-BTD, $89 or Go!Motion, order code GO-MOT, $124 or Go Direct® Motion Detector, order code GDX-MD, $99
Motion Detectors present a more comprehensive record of the experiment since they can produce real-time graphs of an event. For example, when a student walks towards and away from a motion detector, they see instantly that moving away from the sensor produces an increase in a position vs. time graph. This added feedback is especially powerful for visually-oriented learners, and those with fewer math skills. However, motion detectors can produce noisier data due to sound reflecting off of something other than the intended target.

The area of detection for a photogate is much smaller than that of a motion detector, which can help to focus the data on only the event of interest. As a result, there are some events that can only be measured with photogates such as smart pulley (rotational data) and projectile motion with an object such as a marble.

Our starter package for physics includes only the motion detector, while our deluxe package includes both a motion detector and two photogates. For a list of the types of experiments and innovative uses that can be performed with each sensor, see below:

Motion Detector uses:
http://www.vernier.com/publishers/probecorrelation.html?sensor=MD-BTD

Photogate uses:
http://www.vernier.com/publishers/probecorrelation.html?sensor=VPG-BTD

Dynamics Cart and Track System with Motion Encoder, order code DTS-EC, $409 or Go Direct® Sensor Cart (Green), order code GDX-CART-G, $169
Two other attractive, but more expensive options for measuring motion are the Motion Encoder System and the Go Direct Sensor Cart.

The Motion Encoder System adds an optical position sensing system to record cart motion and replaces a motion detector for cart-on-track activities. This system produces high quality position data and it simplifies experimental setup.

The Go Direct Sensor Cart has a built-in encoder wheel for tracking cart position on or off a track. Like the Motion Encoder System, the Sensor Cart generates exceptional data and has the added advantage of working off-track.

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