The goal of this activity was to take photographs of different stages of a water balloon colliding with the ground using a modified contact trigger.  A contact trigger is simply two pieces of metal separated by a thin non-conductive material.  When an object lands on the top metal plate, the two touch, completing a circuit and setting off the flash unit.  We modified this design, because a normal contact trigger only allows the photographer to take a photo of the instant the object hits the trigger, which doesn't allow for different stages of collision to be captured. 

    Our design consists of two flexible metal plates hanging over a table about 4 feet high. The plates are separated by a thin piece of wood, and a string is connected to the top plate.  The other end of the string is tied onto the balloon.  When the balloon hits the ground and the string tightens, the top plate is pulled down into contact with the bottom plate, thus setting off the flash unit.  By changing the length of the string, different stages of the collision can be captured.  With a longer string, the balloon has to compress more in order to tighten the string, so a photo is taken at a later stage than that captured with a normal contact trigger.  In order to capture a photo of the balloon on its rebound, some modifications were made to the apparatus.  By attaching the string to the bottom one and decreasing the distance between the two plates, a rebound photo was able to be taken.  When the balloon hits the ground it pulls the bottom plate downwards, so when the balloon starts to bounce back up, the metal springs back up to touch the top plate and set off the flash unit.  An animation of our apparatus in action is below.

 

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