Setup

 The setup of this essentially a dropping mechanism, a water tank, and the nscesary photographic equipment to accompany it.


First is the water tank, which is simply a glass aquarium that we have filled nearly full with water. There are also three Ziploc bags that are full of sand in the bottom of the tank. These bags are designed to absorb the impact of the objects as they hit the bottom of the tank so that the tank isn't cracked. The reason that we put the sand into bags is so that the sand wouldn't disperse throughout the water every time that it was stirred up. That would eventually make the water opaque and we would therefore not be able to take very good pictures.


Second is the dropping apparatus. In order to support the dropping apparatus, we had to construct a support system with ring-stands, ring-stand rods, and ring-stand clamps. The system constructed is shown in the picture below.




Compared with some actual pictures:



We then attached the final clamp, which serves as the dropping mechanism, to the top horizontal bar. With a quick turn of the clamp, it is now easy to drop an object from the clamp and into the water below.


In order to determine when the timing for the flash should begin, we placed a photogate in the path of a dropping object with the help of yet another clamp as seen in the picture above. when the path between the LEDs in the photogate becomes blocked, the photogate sends a signal to the flash timing apparatus to tell it to begin counting for the flash.


We also needed to construct a timing apparatus to give us an easily changeable and very consistent way to time the interval between the blocking of the photogate and the time the flash is set off. In order to measure the time, we used a computer with a program on it called an intervalometer. This allowed us to input a time into the computer, which would count that time after the photogate was closed to the time that it set off the flashes. One drawback of the program is that it only allowed a delay time of 100 ms. If, however, we moved the cable to the second slot on the output box, the we could add an interval time with a maximum time of 100 ms. This was still not enough to capture the end of the splash, so we moved the plug again to the next slot, which doubles the interval time and adds it to the delay time. This input plug, however, was broken. We therefore moved it to the third and final plug, which triples the interval time and adds it to the delay time. Now we could set off a flash at any time of the flash


We also had to connect the flash to the computer and the photogate. In order to do this, we connected the two leads of the photogate into the input box. The lead from the LED went into the top of the box in the second slot and the lead from the phototransistor went into the side of the box. Next to the input for the LED is a dial for sensitivity, which we set for the middle setting. The input box had two leads that connected it to the output box and also part of a parallel cord that connected it to the computer. The other part of the parallel cord connected the computer to the output box. On the output box, we plugged the output cord into the appropriate plug (see paragraph above). The cord split into two cords in a Y and went into each of the flashes.


Of course, this all requires power to work. There is also a power box that ahs a cord that plugs into the input box. A cord from the input box provides power in series to the output box. The power box plugs into an outlet. The computer has its own cord that also plugs into an outlet. Each of the flashes also have a power cords, which plug into the outlet.

The flashes each attach to a mounting clamp. The flash on the left is attached to one of the ring stands. The other flash is attached to the table leg.


You have probably noticed that I have yet to mention a camera. This is simply because everything else needs to be set up before the camera is of any use. Now that we have everything else ready, we can position the camera about 0.75 m in front of the aquarium. Since we have no adjustable tripods that are low enough to the ground to photograph what we want, we had to improvise. We did find a tripod that was not adjustable, however, and attached the camera to that. We then placed the tripod on top of five physics books so that the books could provide a taller base for the camera. As you can see, the base for this project is physics.

The following settings were used on the camera:

We began the project attempting to view our results using the approximately 3 cm wide and tall LCD display on our digital camera. If we wanted to be able to see any real results of the pictures that we had taken, we had to remove the memory card from the camera, take it down the hall to the computer which had the memory card reader attached to it, wait for the computer to log on, and then wait for the computer to load the picture. Instead of having to do all this, we simply attached an A/V cable from the camera to a TV that we brought into the lab. This allowed us to have instant feedback of our results. If we wanted to view full quality pictures, we still had to use the computer, but this made it easier for preliminary analysis of results.