Overview
Project one
Purpose
Students will consider the interplay of physics sub-branches within a very complicated mechanism.
Theory
A Rube Goldberg machine refers to a ridiculously complicated, multistage mechanical device, which ultimately is used to perform a relatively easy task.
The name is that of a cartoonist whose forte consisted of humorous sketches in newspapers showing absurdly over-engineered contraptions to comb one's hair or open a bottle or the like. Rube Goldberg did not invent the concept.
The typical goal of those who build real Rube Goldberg machines is to use as many kinds of physical interaction as possible, and to amaze spectators.
The palette of interactions comes from the laws of mechanics. This has main sub-branches of kinematics (motion of launched objects), dynamics (forces on any object), energy exchange, inertia (one object colliding with another), rigid-body mechanics (turning objects), thermodynamics (heat flow), material deformations, fluid mechanics, orbital mechanics, and oscillations (such as in a pendulum). All of these except orbital mechanics are accessible when making a Rube Goldberg machine.
One especially elaborate instance of such a machine was used in a music video by OK GO. A team of engineers designed and erected a bewilderingly complex device on two floors of a large warehouse to go with the song. Adam Sadowski was in charge of the project and gave a Ted Talk about it, showing the video at the end. This can be found at the following link on YouTube. The actual music video starts near 7:30.
Procedure
1. Watch the video linked above and pay attention. To watch only the Rube Goldberg machine in operation, skip to 7.5 minutes, but the lead-up discussion is somewhat interesting, too.
Analysis
Please answer each of the following questions in Canvas, and use complete, grammatically correct sentences:
- Pick an interaction from the entire sequence as a favorite: Why was it so interesting? (This need not have a long answer. It's just a matter of curiosity.)
- How many interactions occurred in this Rube Goldberg machine video? In other words, how many stages were there? (Counting them all is subjective and difficult, but don't just give Adam Sadowski's answer; watch once more and try to get a rough count of distinct stages within the mechanism. Write the number inside a complete sentence such as "I counted 126.")
- Out of the array of mechanics sub-branches listed in the Theory section above, are there any that were not used other than orbital mechanics? Specify which one (s).
Project two
Purpose
Students will use vector addition on
the Flat-Earth Model.
Theory Vector addition is easy and useful. To add (24,0) to (0,-7), the 1st numbers are added, as are the 2nd , and the order stays the same: (24,-7). These can be x- and y-positions, velocities, forces, etc.
Which way are the streaks on the side windows of a car going 24 MPH if driving through rain falling at 7 MPH? That’s a vector of . The angle is found by taking the arctangent of the second 2nd over the 1st:
The Flat-Earth Model claims earth is a horizontal disk. The north pole is at the center, “Antarctica” is a rim wall at the edge, and the sun and moon move in circular paths above the disk. If true, it should be easy to measure the sun’s altitude and make predictions.
Procedure 1. Find a cardboard box about the size of a microwave, cut off the top flaps, and set it on its side outdoors at noon as pictured on the right.
2. Cut a coffee-cup-sized hole in the middle of the upper wall and tape a sheet of aluminum foil over it. Poke a small hole in that with a pin or tack.
3 With the sun overhead, even if it is slightly cloudy, a spot of light should show on the bottom surface in the box. Propping the box at a tilted angle may be necessary, but then don’t move it. Mark the box bottom where the spot is at noon, and then again at 1PM.
4. Find a ruler and measure the height from the noon mark up to the foil hole. Let this be . Also measure the distance between the marks. Let this be . Units can be inches, centimeters, whatever but use the same for and .The sun’s ray vector in the box is . This vector can also be used to find the sun’s angle above the horizon.
Fig 1: the box as described
5. The sun apparently moves in an hour. (Call someone in Ft. Worth and ask them what time of day the sun is highest in the sky, if skeptical.) The sun’s height in miles is .
6. If the Flat-Earth model is right, the sun always keeps this height, so after three hours, the spot goes laterally. Find the predicted sun angle above the horizon at 3 PM using . Wait for 3 PM and see if that’s nearly right.
Analysis Please answer each of the following in Canvas using complete sentences:
1. How high up (h) is the sun using the Flat-Earth Model?
2. At what angle above the horizon is the sun at 10 PM using this model?
3. What is the diagonal distance to the sun at 10 PM by this model when its position vector is (10000,h) miles?
4. Did this lab disprove all unpopular scientific viewpoints? Why or why not?