Rube Goldberg

Mechanisms:

• Pushing a ball down a ramp

• That ball goes into a cup attached to a string on a pulley, weighing down left side of pulley

• LEFT: cup comes down to a flat surface and knocks over the first of a sequence of dominoes

• *The last domino in the sequence hits another ball down a ramp with a loop de loop

• The ball finishes the loop and hits scissors which cuts a string

• The string has a straw attached to it, which falls into the final cup when the string is cut

• RIGHT: other platform of pulley comes up, edge hits a ruler

• *Ruler has a nail attached to the end of it; ruler is rotated by the impact and the opposite end pops a balloon filled with water

• The water flows into a funnel

• The funnel directs the water into the final cup

• END RESULT: final cup has water and a straw in it!

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Physics Behind It:
The chain reaction starts with a 43g ball at the top of a ramp. It travels down around 3 inches, converting potential into kinetic energy, and falls down a ramp (energy estimate: initial potential=mgh=.0321 N, final kinetic is the same, minus a bit for friction, so around .03 N). Next, the ball falls into a cup attached to a pulley with a piece of wood on the other side (energy estimate: acceleration of the pulley=9.8(mass of cup and ball-mass of wood piece)/mass of cup and ball=6.98 m/s^2). After that on the right side, the wood hits another piece of wood, giving it an angular impulse (energy estimate: all kinetic energy from wood minus some for friction from the collision, initial momentum=mass of wood x velocity=.026 mxs). Then that piece of wood swings and pops a balloon, which water drains out of into a funnel. As the water flows down, potential energy turns to kinetic as it enters the bottle. On the left side, the cup with the ball falls and knocks over dominoes, a step in which some energy is lost through each collision. The dominoes knock over a 17g ball at a height of 18 inches down a loop de loop (energy estimate: initial potential=.017 x 9.8 x .45=.075N, kinetic final=.075N minus a little for friction).  The ball then transfers all of its momentum to a collision with the scissors, causing the scissors to cut the string and then straw falls into the cup.

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Results:

We faced many challenges in different parts of our mechanisms and worked very hard to overcome them. In the pulley system, a challenge we saw was that the two sides continued to knock into each other, causing either side to lose momentum. This was not a desirable factor for our machine because we needed the right side to have lots of speed in order to hit the wooden peg that would poke the balloon. To solve this issue, we made a border between the two sides so that the cup and wooden piece would no longer touch. We also made sure the right side was fast enough by using a larger ball at the beginning and loading the cup with small objects to ensure that it would send the right side flying up quickly. Doing this we learned the importance of mass and friction in a pulley system and how they can affect each other. 

While the creation of the lever to pop the water balloon wasn’t too hard, getting it to work came with an unexpected challenge. After experimenting with the pulley to get it to be close enough to swing all the way every time, it became evident similar experimenting would need to be done to pop the balloon. Due to the circular nature of the balloon, and how close the lever was against the cardboard backing, the tack often missed the balloon. The tack was tested, and it was sharp enough to pop the balloon. The height and closeness of the balloon was adjusted, however the tack-lever wasn’t at 100%.

Creating the waterpark-like bucket was a harder challenge than first met the eye. Getting the water to come out of the pipe with the funnel attached, and hit the water bucket in the right way so it would tilt was hard. Initially, it was hard to find the right looseness of the holes on the sides of the bucket that the straw went through. Then, it was a challenge to get the bucket to tip, as it just held the water. The first thing tested was adding a weight to one side, so it would tilt that way. This method was discovered after extensive research on how the machines work, however all the weight did was cause the bucket to be already tilted as far as it would go. Water would hit the bucket and eventually just pour out due to the angle, which isn’t the same as the buckets at water parks. (Various weights were tested). The next idea was to put a wall in the bucket, so that the water could only fill one side of it, causing it to lean that way. While this did eventually work, it was hard to place the funnel and the water bucket mechanism together on the machine. The water bucket’s purpose in this machine was to pour the water into a funnel, which would carry it to the same cup the straw would drop into. However upon assembly, the ending spots of the bucket and the scissors were not the same. For this reason, the bucket is missing from the final design, and the water just poured straight from the water balloon into a separate water bottle. 

For the last mechanism, the scissor cutting the string releasing the straw to fall into the cup, the main challenge was getting the scissors to cut the string. Factors that affected this outcome included the sharpness of the scissors, placement of the string in the scissors, and the force required to close the scissors hard enough to cut the string. The sharpness was a quick fix, finding the sharpest pair of scissors is pretty easy. The placement of the string relied on how long it was, how much it stretched, and how far open the scissors could rest. With the addition of push pins, it was easy to manipulate where the string was placed and made it so that it could be moved anywhere. To increase the chances of the ball hitting the scissors, we experimented with adding a plate to the handle of the scissors but found that there was some added movement that took away from the force applied to the scissors. Without the plate, the ball needed to land more precisely however the trade off was a more forceful close of the scissors which we deemed more important to the functionality of the mechanism.

Another issue we faced was the connection between the cup on the pulley coming down and the ball rolling down the loop de loop. Sometimes the cup would land in different places and not be able to push the dominoes, then sometimes the dominoes would not fall properly and would not push the ball with enough force. We fixed these problems by adding a wall to the right of the cup, ensuring consistency in where it lands and by messing with the positions of the dominoes and also taping two together to give the reaction additional mass, creating a greater impulse on the ball. In the end, there was still inconsistency with this part of our design because of us not building in enough space to have a proper reaction of the dominoes, so they fell unevenly and did not push the ball consistently.