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Rubberband powered boat

  1. Dec 3, 2012 #1
    I am doing a rubber band powered boat for a project, but I'm not too sure as to what physics theory I can incorporate into it. We made a small wood board boat and powered in using rubber bands and tested to see how long it took to reach the end of the bath tub. Every time we added one more rubber band and saw that when we added the 8th rubber band, the boat started to sink. When we added the 10th rubber band, the boat flipped over.
    How do I know the energy in joules?
    I would really appreciate your help.
     
  2. jcsd
  3. Dec 3, 2012 #2

    jedishrfu

    Staff: Mentor

    Make sure you're using the same strength rubber bands ie when you use the rubber band to lift a small weight it stretches the same length for each rubber band.

    You could try pulling the watercraft with a rubber band to see how much drag force the boat has and use hooks law (assuming the rubber band follows it) to compute a force value. Then from there take measurements of the time and the distance to the end of the pool vs number of rubber bands used.

    The drag would be proportional to the speed of the boat.
     
    Last edited: Dec 3, 2012
  4. Dec 3, 2012 #3
    These are the results:

    #rubber bands Time to reach end of tub (s)
    1 Did not reach
    2 8.5 s
    3 4.8 s
    4 4.2 s
    5 3.5 s
    6 3.4 s
    7 3 s
    8 3.5 s (began sinking)
    9 3.6 s
    10 3.7 s (flipped over)
     
  5. Dec 3, 2012 #4
    I used the same strength of rubber bands. The above data is all I have to come out with a theory and calculations. The bathtub distance is 4.5m. What exactly would I be able to calculate with this data?
    I know that the more rubber bands we added, the faster the boat traveled.
    I'm sorry I have not taken physics before, thus I am very lost.
     
  6. Dec 3, 2012 #5

    jedishrfu

    Staff: Mentor

    what is the distance traveled in meters?

    Could you use KE = 1/2 m v^2 to determine the effective kinetic energy as you add each rubber band?
     
  7. Dec 3, 2012 #6
    'm' stands for mass of the boat?
     
  8. Dec 3, 2012 #7

    jedishrfu

    Staff: Mentor

    yes its the mass of the boat preferably in MKS units.
     
  9. Dec 3, 2012 #8
    Oh ok. Thank you very much for your help. I really appreciate it! :)
     
  10. Dec 3, 2012 #9
    I have one more question. Why did the boat start to sink when we added the 8th rubber band? And why did it flip over when we added the 10th?
     
  11. Dec 3, 2012 #10

    jedishrfu

    Staff: Mentor

    too much power supplied is my guess.

    when a boat is pushed thru the water the front rises. It rises higher and higher based on the speed and eventually the speed is too great and it flips. I'm guessing it flipped bcakward right?

    try pushing the boat your self and you'll feel the drag from the water pushing back. If you use your finger and push real hard it should flip.
     
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