Physics Frontiers

Page

Dynamics with a Smartphone

Tracker is a free video analysis and modeling tool built on the Open Source Physics (OSP) Java framework. It is designed to be used in physics education. Visit the Tracker Site to download the installer software appropriate to your operating system, e.g. Windows, Mac, Linux. The package may be used for:

  • Manual and automated object tracking with position, velocity and acceleration overlays and data.
  • Center of mass tracks.
  • Interactive graphical vectors and vector sums.
  • Much more.

Introductory Guides and Support

Note: tracker requires Java 1.6 or higher so check that your version is up to date and install if necessary.

Example 1

Acceleration of a tennis ball in free fall.

Free Fall Video

Tracker works best when the object to be tracked is brightly coloured and has a background which provides a clean contrast. However, there is no need to be over fussy. In this experiment, A2 sized white cards are taped together and hung on a wall or from a ceiling. A whiteboard or clutter free wall works just as well. A tennis ball (yellow) is dropped in front of the cards while the smart phone records the drop. Best results are obtained if the smartphone video setting is set to at least 60 frames per second (fps). If 90 fps is available, it works really well – gives clear free-fall object images while still keeping video file size relatively small. If you want to catch really fast action then using the slow motion option on your phone,  ‘SloMo’ , is recommended. Typically this will record at 120 fps. Higher frame rates may be available. However, remember that file size will scale with frame rate so try to reduce video duration to keep video file size down. Generally, your analysis will use a clip which is a couple of seconds in duration so no need to record feature films. Once you have your video recorded and transferred to your laptop, you are ready to start your video analysis.

When setting up your experiment, remember to add an object of known length to the field of view to allow ‘distance calibration’ using the Tracker ‘Calibration Stick’. A ruler or meter stick is generally available and good for this.

Fall of tennis ball tracked frame by frame. Graph shows straight line fit to a drop velocity versus time plot. Slope of line yields a value of 9.4 m/s^2 for g.

 

Using the ‘Autotracker’ tool in Tracker to follow a pendulum recorded using Video ‘SloMo’ mode (120 fps) on iPhone 6. Track data (x position of pendulum) is plotted, top right. The pendulum period may be read from the graph.

 

School Physics and Applied Maths

Some Leaving and Junior Certificate Physics, and Leaving Cert Applied Maths which Tracker could help reinforce.

Mechanics

  1. Measurement of Velocity and Acceleration
  2. To show that Acceleration is proportional to Force
  3. Verification of the principle of conservation of Momentum
  4. To show that Acceleration is proportional to Force
  5. Verification of Boyle’s Law
  6. Investigation of relationship between period and length for a simple pendulum and hence calculation of “g” (Higher)

Sound

13 & 14. Investigation of the variation of fundamental frequency of a stretched string with length and tension

Junior Certificate

OP 1 Displacement, Velocity, and Acceleration Graphs

OP 8 Weight, Feather and a Stone falling.

Others?

Applied Maths

  • Linear Acceleration
  • Projectiles
  • Collisions
  • Circular Motion
  • Simple Harmonic Motion
  • Rigid Body Motion

Acknowledgements

Thanks to John Kelly for setting up Tracker on the laptops and all the lab prep for the workshop. Thanks also to Eamonn Campbell for his help with the video recording.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s