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Home Interactives 1D Kinematics Motion Detector Notes

Motion Detector Notes

Notes:

The Motion Detector Interactive was made to work with phones and tablets in Portrait mode. While the intent was to use the Interactive with phones and tablets, it will also work with Chromebooks, laptops, and desktop computers. The only requirement is that the device the Interactive is used on is equipped with a camera that can focus on a printout of an ArUco marker. The Marker PDF can be used in situations in which students are holding a phone or tablet and walking towards or away from the stationary marker. We also provide a Quarter-Sized Marker to be used in situations in which space is limited and/or movement is not possible. These markers can be moved towards or away from the computer with arm movements.

Teaching Ideas and Suggestions:

We believe this Interactive is best used in the earliest stages of a learning cycle on kinematic graphing. We have two other very popular Interactives - Pace Tracer 1 and Pace Tracer 2 - which can be used in later stages of the learning cycle. The Pace Tracer apps provide students with a game-like challenge of moving in a specific manner so as to match a pre-made position-time graph (Pace Tracer 1) or velocity-time graph (Pace Tracer 2).

Motion Detector uses the camera of the device as a motion-detecting instrument. With most operating systems, the user of the device must first give permission to Motion Detector to use the device. (It's safe. You have our pledge that no video is collected by Motion Detector. It is only used for motion detection). The user then calibrates Motion Detector by pointing the camera at the printed ArUco marker from a distance of 1 m away. This 1-meter distance does not need to be precise; from the tip of the finger on an outstretched arm to the nose when standing sideways can be called 1 meter. Once calibrated, a small dot will appear on the position axis of the graph. As the phone is moved towards or away from the marker, the dot will move along the axis. When ready, the student can tap Go and move in an intended manner. The position of the phone is marked on the graph in real time over the course of 8 seconds. For reference, the + direction is away from the ArUco marker.

Motion Detector includes a display toggle for the two graphs. Tapping the hide/show button above the graph will toggle its visibility from visible to invisible. This is a handy feature for classrooms wishing to exclusively study position-time graphs or velocity-time graphs.

We recognize that not everyone is a fan of phones being used in a classroom. And in some places, they aren't even permitted. We get it! But Motion Detector is not reliant upon a phone. It simply requires a device with a camera and a browser. School issued Chromebooks, laptops, and tablets also work. And the device with the camera doesn't even need to be the device that moves. If you have a desktop computer, then have the students hold the markers and move with the markers as the computer's front-facing camera acts as the detector. Students will see their motion plotted on the monitor as they move.

Motion Detector does a great job with position-time graphs. Like most motion detection systems, velocity-time graphs will display results that may be less than satisfying. For instance, when detecting the intended-to-be-constant-velocity motion of a student, the graph will unlikely be a horizontal line. It is more likely to be a jagged, zig-zag line that is grossly approximated as a horizontal line. We have found better results with velocity-time graphs by using a cart and low-friction track as the moving object. Equip the track with an end bracket to prevent the cart from rolling off either end. A computer or Chromebook can be placed about 25 cm from the track's end. A printed marker can be secured to a lightweight but rigid surface and secured to the cart. A gentle push will send the cart across the track at near constant speed. Motion Detector should be able to detect the movement of the marker and plot the motion. Accelerated motions can be analyzed using a cart in motion along a gently inclined track.


The Physics Classroom has not yet provided a classroom-ready activity sheet for use with this Interactive. There are likely a load of motion detector type activities readily available from other sources that can be adapted for use with Motion Detector. An alternative to providing an activity sheet is to provide students with some questions to explore. Here's a few starter questions that you might find useful:
  1. What does a position-time graph look like for an object at rest?
  2. How is a position-time graph for an object moving in the positive direction (away from the marker) distinguished from the graph for an object moving in the negative direction (toward the marker)?
  3. How is a position-time graph for an object moving fast distinguished from the graph for an object moving slow?
  4. How is a position-time graph for an object moving at constant speed distinguished from the graph for an object moving with a changing speed?
  5. How is a position-time graph for an object that is speeding up distinguished from the graph for an object that is slowing down?
  6. What does a velocity-time graph look like for an object at rest?
  7. How is a velocity-time graph for an object moving in the positive direction (away from the marker) distinguished from the graph for an object moving in the negative direction (toward the marker)?
  8. How is a velocity-time graph for an object moving fast distinguished from the graph for an object moving slow?
  9. How is a velocity-time graph for an object moving at constant speed distinguished from the graph for an object moving with a changing speed?
  10. How is a velocity-time graph for an object that is speeding up distinguished from the graph for an object that is slowing down?

Related Resources:

There are numerous resources at The Physics Classroom website that serve as very complementary supports for the Motion Detector Interactive. These include:
  • Physics Interactives:
    Motion Detector is a great starting point for an interactive learning experience. Why not try one of our other Interactives as a follow-up? You may particularly like our Graph That Motion, our Kinematic Graphing, and our Graphs and Ramps Interactives.
  • Minds On Physics Internet Modules:
    The Minds On Physics Internet Modules include a collection of interactive questioning modules that help learners assess their understanding of physics concepts and solidify those understandings by answering questions that require higher-order thinking. Missions KG1 - KG3 of the Kinematic Graphing module provide great complements to this interactive for position-time graphs. Missions KG5 - KG7 make great complements for velocity-time graphs. They are best used in the middle to later stages of the learning cycle. Visit the Minds On Physics Internet Modules.
  • Calculator Pad:
    Are you ready for calculations and problem solving. The Calculator Pad is our go-to section for that. If you haven't seen our 2022 update, then you need to check it out. You will find a couple of problem sets on the analysis of position-time graphs.

    Visit Kinematics Chapter of The Calculator Pad.
  • Science Reasoning Activities:
    Science classrooms should be filled with reasoning activities. There is one related activity in the Kinematics section of the Science Reasoning Center that will challenge students to employ close reading, data analysis, and logical reasoning. The activity is named ...

    Kinematics

    Visit the Science Reasoning Center.


Additional resources and ideas for incorporating Motion Detector into an instructional unit on kinematic graphing can be found at the Teacher Toolkits section of The Physics Classroom website. Visit Teacher Toolkits.


Credits:
A special thanks goes out to Chris from Nerd Island Studios (makers of SimBucket) for putting together and testing this Interactive.

Visit: Motion Detector Interactive