The Polar Express. Section: D1. Group Members: David Fellers Shannon MacAdams Ryan McGranaghan Ryan Whitted

Transcription

1 The Polar Express Section: D1 Group Members: David Fellers Shannon MacAdams Ryan McGranaghan Ryan Whitted

2 Overview This device uses a series of steps to accomplish the simple task of raising a kilogram of weight the height of a meter. The device utilizes many inexpensive materials with no one item weighing over 2.5 kg. Using minimal space (specifically 0.5 m wide x 1.0 m long x 0.5 meter high), the device manually starts with a billiard ball, energy is transferred to a marble, a mousetrap is engaged, and a car rolls diagonally down a ramp while a counterweight provides enough force to pull the rest of the kilogram the whole length of a meter within ten seconds. Design Process We began solely using the concept of a ramp. The rest of our ideas followed logically in order to allow the ramp and car to function properly. In fact, the video examples of Rude-Goldberg devices were extremely helpful in the brainstorming stage, and even when we began construction. More specifically, we obtained the idea for the ball falling into cloth to raise another ball from one of the Japanese videos. Furthermore, we wanted at least four energy transfers so we could classify the system as a true Rube- Goldberg device. Moreover, to keep the mechanism within the size guidelines without sacrificing our vision, we maximized our work area by cutting some heavy duty cardboard that we got at Home Depot 1.0 m x 0.5 m and built the ramp 0.5 m high. Each measurement was carefully conducted in order to enable the weight to be lifted the full meter. We had to manually begin the process with a billiard ball. Initially, we began the billiard ball on a ramp going into the taut part of the cloth to project the marble. However, this process did not run as smoothly as we planned due to the fact that the repeatability of our results was inconsistent, thus we took out the ramp and replaced it with a raised platform that sits at an angle so the ball can drop vertically onto the cloth instead of horizontally. The tunnel and track that led to the mousetrap was the easiest part of the project and required only a small amount of time. However, perhaps the biggest complication we encountered came from the fact that we initially planned for a gate to be holding the car at the top of the ramp. This approach was unsuccessful due to the fact that there was simply too much weight on the car. We could not figure out how to make a gate that would not only resist buckling at the Newton weight of the car, but could also be pulled out with relative ease. Therefore, we decided to use the spring energy of a mousetrap that was rigged to release a string that was attached to the back of the car. When we tested this out, everything worked smoothly except that the kilogram of weight did not lift the required length. We then engineered a small pulley and added a counterweight of about 2.0 lbs that pulled straight down and was released at the same time the car was released by the mousetrap. The weight was easily lifted the full meter well within the time constraint of ten seconds. Design Description The device begins with a billiard ball that falls from a height of approximately 0.25 m onto a taut cloth. The cloth gives and the marble on the loose end of the cloth is projected into a cup that acts as a tunnel for the track. The track leads to the sensitive end of the mousetrap and the mousetrap is engaged. A string tied to the spring on the mousetrap releases the strings that are attached to the counterweight and the car, sending

3 the car down the ramp and the counterweight straight down. The kilogram of mass is lifted off of the ground quite quickly to the full length of a meter, accomplishing the simple task within the time, weight, and size constraints. Sketches Mouse trap engaged. The car and the counter weight. The transfer of momentum from billiard ball to marble.

4 Stored Energy Mass billiard ball=.15 kg Height of billiard ball=30 cm =.3 m Energy of billiard ball= mgh =.15*9.81*.3 = Mass marble= 8.9 g =.0089 kg Height of marble=12 cm=.15 m Energy of marble= mgh =.0089*9.81*.15 =.0131 J Spring constant=.0953 Deflection of spring= 1/2πr2 =1/2*π*.05= m Energy of mouse trap= 1/2kx2 = ½*.0953* = J Mass of cart= 2.5 kg Height of cart=.5 m Energy of cart= mgh = 2.5*9.81*.5 = J Mass of counterweight=.907 kg Height of counterweight=.45 m Energy of counterweight= mgh =.907*9.81*.45 = 4 J Mass to be lifted= 1 kg Final height lifted mass= 1 m Energy to lift mass= mgh = 1*9.81*1= 9.81 J Total energy= = J Efficiency = 9.81/ = 58.68%

5 Pricing of Materials Base $2.50 Ramp $1.00 All cardboard $1.00 Tape $2.00 Cup $0.05 Thumb tacks $0.04 Nails $0.10 Mousetrap $0.35 Track $0.50 Cloth $0.20 Car $1.50 Strings $0.25 Weights $3.00 Polar bear $1.00 Pulley $0.50 Billiard ball $1.00 Marble $0.05 Baggie $0.05 Rubber Band $0.05 Total $15.14 Conclusions Our group felt confident in our system of reactions going in to class based on the information that the test run before the presentation was a complete success. However, complications arose when we tested the project in presentation. First of all, the marble did not make it to the mousetrap the first two runs and the tape that held the strings connecting to the car and the counterweight was too sticky and did not release. These mistakes were simply overlooked problems by our group, not defects in our Rude- Goldberg device. Other than these few difficulties, the project was overall a success. The whole team worked very well together and the work environment throughout was one of collaboration and constructive problem solving. One of the only things we could have done differently was to begin brainstorming earlier so we would have a better visualization of the project before construction began.