Equipment:

    A Squiggle BallTM is a children’s toy made by Hart Enterprises.  Inside of each ball exists a battery-powered motor that rotates at approximately 3 rev/s.  This allows the balls to move in unpredictable paths.  The balls each have a radius of 4 cm and a mass of 120 g.  Around their circumference, they have a rubber rim that allows them to grip the ground better.  These balls come in many different colors.

Fig. 0. Squiggle BallTMs

Part I: Equation of State

Setup:  On top of a ribbed mat, a 70.6x 35.0cm rectangle of PVC pipes is placed. This rectangle is raised by wooden blocks and is clamped to a table using two C-clamps.  Underneath the map, metal rods are placed around the perimeter of the rectangle to ensure that the balls do not become stuck in corners.  This rectangle is divided into two parts by another PVC pipe which is left free to move (termed piston).  Inside the left section, two Force Sensors are placed on both ends of the free-moving piston.  They are held up by a rod placed parallel to the table.  This rod is supported by a ring stand and taped to the rectangular frame to keep the Force Sensors in place.  Electrical tape is added to the frame to keep the Force Sensors at a constant angle with respect to the piston.  The Force Sensors are connected to Channel A and Channel B of the Signal Interface which is then connected to the computer.  Data Studio 1.6.1 is used to take the data.  Inside the right section, 3 to 6 Squiggle BallTM’s (mass=120g and radius=4.0cm) are placed.  These balls contain battery-powered motors that rotate the shell at approximately 3 rev/s.  Diagrams and pictures of the setup are shown below. 

Fig. 1. Diagram of the experimental setup for 3 balls.

 

 

Fig. 2. Aerial view of experimental setup for 4 balls

Fig. 3. Horizontal view of setup

Procedure: Fresh rechargeable batteries were placed in the Squiggle BallTMs before data was taken every day.  The movable piston and Force Sensors were placed x cm's from the right wall of the frame.  The Force Sensors were then taped down to the frame.  The piston was moved away from the Force Sensors and the balls were turned on.  The Force Sensors were tared at this point to zero the effect of the balls colliding with the other walls.  The piston was returned to its original place and Data Studio was told to start taking data.  Data Studio recorded the force on both sensors every .005s (at a frequency of 200Hz).  10 runs were done at each position for 30s.  This experiment was preformed at x= 15, 20, 25, 30, 35, 40, 45, 50, and 55 cm for 3 and 4 balls and at x= 20, 25, 30, 35, 40, 45, 50, and 55 cm for 5 and 6 balls.  The bar on the left and right hand side were marked at these lengths for consistency.  There were small variations in this experiment during data taking.  For 3 balls, the rod was not taped to the frame.  Instead weights were placed behind the Force Sensors.  Also, the Force Sensors were parallel to the ground instead of being suspended upward as in subsequent experiments.  At x=55cm for all runs, the Force Sensors rested against the frame instead of tape.  During all runs, there were times when balls got stuck on a wall or when their motor stopped functioning.  A slight push was given to the balls at this time.

Part II:  Pressure Fluctuation Machine

Setup:  The same rectangular frame, ribbed mat, movable piston, and squiggle balls were used in this experiment.  The Force Sensors were removed and a piece of cardboard on a light metal post was attached to the moveable piston with electric and masking tape.  A Motion Sensor was placed on a block resting on the Signal Interface.  This Sensor was on the left hand side of the wall and placed perpendicular to the cardboard.   The motion sensor was connected to the interface which was in turn connected to the computer.  Squiggle BallTMs were placed on either part of the frame.  See the diagram below.


Fig. 4. Diagram of the experimental setup for 3 vs. 3 balls.

 

Fig. 5. Aerial view of setup for 3 vs. 3 balls

Procedure:  Fresh rechargeable batteries were placed in the Squiggle BallTMs.  The partition was placed at x=35cm, approximately in the middle of the frame.  For the first part, 3 squiggle balls were placed on either sides of the partition.  The balls were turned on, the piston released, and DataStudio was told to take data.  For 30 minutes, DataStudio recorded the position of the cardboard and the time every 0.005s (200Hz).  For the second part, 4 balls were placed in the left section and 2 balls were placed in the right.  Again, the position of the piston was recorded for 30 minutes.  During both of these runs, there were times when a ball got stuck on a wall or when a balls' motor stopped functioning.  A small push was given to the balls at these times.