PocketLab Joins Ozobot to Study Position, Velocity and Acceleration Concepts

Ozobot (ozobot.com) is a tiny one inch diameter line-traveling robot that can be used in conjunction with PocketLab to easily study the physics concepts of position, velocity, and acceleration and their time graphs.  PocketLab is simply taped to the top of an Ozobot using double-sided mounting tape.  In other words, Ozobot gives Pocket lab a ride.  The photo below shows this setup, with Ozobot following a 1/4" heavy black line drawn with a chisel tip marking pen.

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A magnetic ruler can be easily constructed to capture position/time information on the Ozobot/PocketLab duo. The photo below shows the magnetic ruler.  Small neodymium magnets are taped 15 cm apart on a stick that can be purchased at hobby shops such a Michaels.  PocketLab is set to record values of magnetic field magnitude.  As the PocketLab/Ozobot pair travel along the line, the magnetic field magnitude rises to a peak when reaching each of the magnets on the ruler.  The data file created by the PocketLab app can then be used to determine the times for each of the peaks.  With position and time known, a graph of position and time can then be constructed, perhaps in Microsoft Excel.

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CONSTANT SPEED EXAMPLE
 
The movie below shows data captured when Ozobot/PocketLab move at a constant speed along the line.
The two charts below were created using Excel with raw data from the PocketLab app magnetometer magnitude.  It is seen that the peaks are very close to being equally spaced in time, roughly 2 seconds apart.  With the distance between magnets fixed at 15 cm, velocity is therefore constant. The slope of the position versus time chart tells us that the velocity is about 7.546 cm/s, as shown by the linear regression data from Excel.  The Excel file is attached for anyone interested in viewing its details.
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CONSTANT ACCELERATION EXAMPLE
Ozobot can be programmed using OzoBlockly (ozoblockly.com) in a way that causes Ozobot to accelerate rather than travel at constant velocity.  The OzoBlockly program shown in the figure below was used in this investigation.  Ozobot begins at a speed of 35 mm/s and then increases as it approaches each of line intersections at the magnets by 10 mm/s.  Because Ozobot is carrying the weight of PocketLab, the speeds are actually somewhat less.
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The movie below shows data captured with Ozobot/PocketLab traveling with  acceleration.  You will note that as its speed increases, the distance between peaks of magnetic field magnitude decrease.
The two charts below were created using Excel with raw data from the PocketLab app magnetometer magnitude.  Again, we note that the peaks are more closely spaced as time progresses.  The thin black straight line on the position vs. time graph clearly shows that the curved blue line implies acceleration.  When a linear fit is done on the velocity vs. time chart, we find that the average acceleration is about 0.2932 cm/s/s.  The Excel file is attached for anyone interested in viewing its details.
magrgaphaccel5positionvelocityvstimel7

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