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:
- What does a position-time graph look like for an object at rest?
- 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)?
- How is a position-time graph for an object moving fast distinguished from the graph for an object moving slow?
- 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?
- How is a position-time graph for an object that is speeding up distinguished from the graph for an object that is slowing down?
- What does a velocity-time graph look like for an object at rest?
- 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)?
- How is a velocity-time graph for an object moving fast distinguished from the graph for an object moving slow?
- 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?
- How is a velocity-time graph for an object that is speeding up distinguished from the graph for an object that is slowing down?
There are numerous resources at The Physics Classroom website that serve as very complementary supports for the Motion Detector Interactive. These include: