The Vernier Motion Encoder System: Motion Encoding Made Personal

The Vernier Motion Encoder System marks a significant shift in the science teacher’s ability to transition between the conceptual, formula-based physics of motion to the “real world” application of those concepts and formulas—and here’s the big news—without the need for disclaimers explaining away anomalous data, inconsistent graphs, and the general background noise of low resolution measurements. While it is possible to argue that the essence of a motion activity transitions from concept to concrete without using meaningful data since the students at this level are able to imagine what was supposed to happen, by actually capturing accurate and precise motion data, the traditional conclusion of the motion lesson is actually just the beginning of what is now possible to experiment with and visualize.

While it would be easy to dismiss all the good science taught with primitive methods, instead the simplicity, accuracy and operational speed of Vernier’s Motion Encoder System provides students not only a crystal clear insight into the nuts and bolts of motion, but also raises the bar on the subtitles and nuances of motion through actual hands-on experimentation and, if you will, science play.

Vernier describes their paradigm shift somewhat dryly as, “The encoder strip consists of alternating black and white bars with a 4 mm period, allowing the optical sensor to detect the passage of the bars as the cart moves. With two sensors appropriately placed, a change in position with 1 mm resolution can be determined, as well as the direction of travel. A narrow infrared beam transmits motion data to a receiver.”

This descriptive paragraph reminded me of a NASA STARDUST announcement where a sample return mission brought back some comet material that contained features known as CAIs or calcium aluminum inclusions. The excitement of CAIs is in their status as one of the first solids to condense out of the solar nebula after the birth of our solar system.  What NASA should have announced is that comets contain material older than the earth! And let the details shake out once the reader’s attention was secured. Check out this link to a NASA/JPL instructional product that adds more humor and exclamation points to comet science.

cart-n-sensorVernier, in their humble pursuit of elegant science teaching solutions, has produced a motion track the length of a tall student’s arm with carts the size of human hands and a motion resolution at the limit of our finger fine motor skill!

Well, OK, maybe it’s not quite as exciting as being truly older than dirt, but given the overwhelming quantity of our brain that is devoted to exploring the world with our hands, the Motion Encoder System has just brought the fundamental principles of motion into a bio-conceptual arena that we humans are uniquely prepared to explore.

Continuing the theme of the old ceiling becoming the new floor, the Motion Encoder System can first make the abstract concrete, and then provide a safe and power playground to visualize motion data as the actual motion is happening, but then become a testing instrument itself as students mentally explore motion beyond the fabricated universe of a metal track, low friction vehicles, and infrared sensors. In other words, once the foundations of motion are understood, the Motion Encoder System itself becomes a tool in a larger exploration toolbox.

For example, imagine what the motion vs. time graph looks like if you centered a car on the level track with the entire track able to roll back and forth on “bearings” of smooth round pencils. Consider sliding the track to the right while the sensor is on the left side of the track. Did the car move? Or is it relative? Was the motion uniform? Did the car continue to move when the track stopped? You might be asking, “What a practical application of this tangent of questioning?” How about the crash landing of the Genesis spacecraft?

Genesis was a NASA mission that collected solar wind particles on special tiles of various elements. The collection of impregnated hexagons were sealed in their sample return capsule and flown back to earth where upon reentering the atmosphere, the parafoil failed to deploy. Due to the extreme fragility of the pure elemental wafers, landing on the ground was ruled out and the plan was to pluck the floating spacecraft out of the air by a highly trained helicopter pilot using a giant hook suspended from his craft. Unfortunately, as often happens, Murphy’s Law came home from vacatsledion early and at just the wrong moment. And this particular instance is not just a loose reference to Murphy’s Law, but in fact a historical repeat of the foundational mistake that potentially created the so-called Law in the first place.


You see Murphy was a real engineer named Edward Murphy Jr. who did real science with real people and used real data collection sensors. During the rocket sled g-force deceleration testing in the late 1940s. Murphy thought it would be a good idea to insert strain gauges into the harness of the rocket sled in order to measure the actual g-forces experienced by the test subject. After the initial run using a chimpanzee, the sensors read zero. Upon further inspection, it was discovered that every sensor was wired backwards thus unablecrash to record the deceleration. In the case of the Genesis Sample Return Capsule, an onboard accelerometer was included to detect atmospheric resistance on the capsule through deceleration which would then signal the deployment of the drogue parachute further slowing the capsule velocity down to a safe parafoil release speed. Except the accelerometer was installed upside-down. The sensor never detected the slowdown. The drogue chute never deployed. The parafoil never unfolded. And the entire 450-pound sample return capsule never hesitated when it slammed into the Utah desert at 193 miles an hour. (From a purely scientific viewpoint, however, the impact did provide an excellent example of meteoritic cratering complete with crater rim, rays, and reverse stratigraphy.)

 So back to the main question…what will the graph look like if the track moves instead of the car? And now try to visualize which direction an accelerometer should be pointed (up or down) in order to detect a spacecraft slowing due to the atmosphere. Should it point in the direction of travel or the opposite? Are you sure? Are you willing to bet $264 Million on it?

Or perhaps collisions are of interest. The Vernier Motion Encoder System includes two carts, one with a sensor, and one with a retractable spring plunger, and both carts with magnetic and hook-and-pile endcaps.

cart-w-massInertia is another aspect that plays very well with real-time motion data collection. But first a minor digression. A funny thing happened on the way to the Newton’s Cradle demonstration. The teacher was prepared to share the magic of conservation of momentum when it occurred to her that the usual explanation of the balls motion is actually a violation of the very law she was excited to demonstrate. If momentum truly is conserved, then the dropping of two balls on one side would not produce two balls on the rising other side, but rather one ball rising with the conserved momentum of two balls. Physics is not a democracy. There is nothing that would divide up the momentum fairly between the two receiving balls giving them an equal chance to fly away. The solution must be that dropping two balls is not one event, but two. And on the far side, two corresponding results occur. In other words, one ball is dropped, then another ball is dropped, and one ball rises from the first event followed quickly by the second ball from the second event. Two balls is two events happening at two different moments in timinsole1e. Before the furthest out ball can fall, all inner balls must be out of the way. In fact it is quite similar to how we cause traffic jams on unobstructed highways, and why the interval lights on on-ramps keep traffic flowing. Explore the oxymoronic concept of “Moving Jams” if you want to learn more about traffic psychophysics.


Click for motion.

So back on task. When two carts are used on the track, basic applications of F=ma can be explored where one or both carts are moving in various combinations of speed and direction simulating head-on collisions and rear-end collisions. The spring plunger softens the impacts while preserving the result. And the inquiry can run from the carts to the graphs through prediction, or take the inference route where the graph is interpreted to hypothesize the nature of the collision.I could imagine a forensics presentation reenacting an accident using the Motion Encoder System from data graphs generated during the crime scene investigation.

iphoneCollisions can also be used to inspect dampeners such as those in shoe insoles. By inserting the insole between the spring plunger on the cart at the bottom of the inclined track, the rebound of the sensor cart can measure the difference between various insole’s ability to absorb shock.

And yet another tangent of exploration deals with seatbelt use. When turned loose with the track, I noticed a student place her iPhone on the cart. The iPhone was running a seismograph app, and the student was playing the with the “look” of an impact as measured by a “third party” along for the ride. If the iPhone was held in place, the majority of the impact force was consumed by the spring. If the iPhone could slide off the cart, a much stronger impulse was recorded when the iPhone eventually hit something with less elasticity than the spring cart.

In the end Vernier has again offered teachers a powerful tool that provides students with the ability to explore the intricacies of motion, this time with an arms-length of track using a hand-sized cart measuring at the resolution of finger dexterity. In other words, the Vernier Motion Encoder System makes motion personal.


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