The Experiment

These are the steps that I took to conduct the experiment:
1.  Fill a bathtub with water and ensure that the submarine does not touch the bottom.
2. Fill the submarine with enough water such that it does is half-submerged in the water. (Volume varies depending on the size of body of the submarine)
3.  Ensuring that the water from the submarine body does not leak, turn the submarine 30 times so that the rubber band in the body will be twisted 30 times. Keep this constant throughout all the different trials.
4.  Determine a starting line in the bathtub. Slowly let go of the submarine and start the stopwatch at the same time.
5.  Stop the stopwatch at 30s (time should be kept constant throughout all the trials). Measure the distance that the submarine travelled.
6.  Repeat the experiment 3 times.
7. Cut 2 cm (markings) off the propeller to test for the next round.. 
8. Repeat steps 1-7 until the length of the propeller reaches 1 cm.
9. Compare and contrast the results.

How to twist the submarine: (twist it 30 times)

Initially, when we put the submarine into the water (with the modified body and propeller) it still did not work.

After observing how the submarine moved, I realized that I did not have enough water in the body to keep the submarine stable. Hence, I added more water so that the submarine will be steadier. Besides that, I also observed that the body of the submarine was spinning too, which was not supposed to be the case. Only the propeller should be spinning. I presumed that it was the lack of stabilising fins that caused this observation. Lastly, the submarine kept going off track and when it hits the side of the bath tub, it will lose kinetic energy. In order to resolve this, I decided to use a chopstick to guide to submarine such that it would not hit the side of the bath tub.

Modifications that I made:
1. Added more water into the body of the submarine 
2. Added more and longer stabilising fins (using chopsticks)
3. Used a chopstick to guide the movement of the submarine

I wasn't able to video all the experiments. Hence, here is the last experiment where the propeller is at 1cm. The video shows that whole process which I used for the previous trials as well.

Next post will be on the results!