Rube Goldberg Machine
By: Matthew Stark
Tags: Physics

STORY

When coming up with a design for a Rube Golberg project, I looked around my room for objects to use. The first object that caught my attention was my bookshelf, full of many books that I haven’t read since middle school. These old books inspired me to create a library themed machine using my favorite childhood books. The story of my machine is therefore a representation of my childhood story and my love for reading.

The Reading Machine

BUILD PROCESS

My build process started with one question: “How can I incorporate books into a Rube Goldberg machine?” The first idea that came to mind were to use the books as dominoes. As a kid, I always enjoyed setting up wooden planks around my house and knocking them down with one push. So, I decided to use the wooden planks to knock over small books, which would knock over larger and larger books.

The machine could not start with a domino, however, so I decided how to implement the marble in the PVC pipe first. I figured that the best way to maximize the initial energy of the machine was to start the marble high up to increase potential energy. My idea was to have the marble hit an upright book, which would fall over and trigger the next section.

When brainstorming more ideas to incorporate books, I came up with the idea to turn one into a lever. By laying a book on a small rod and placing a ball on one end, I created a seesaw mechanism that would activate when the one side was pushed down. The book from the previous section would fall over, causing the seesaw to tip and allow the ball to roll down the track.

I set up the ball to knock into the first wooden domino, triggering the reaction I described earlier. Later, I added twists and turns to extend the length of the machine. After the dominoes knocked down the books, I decided to incorperate a pendulum. I used my fan with a ball and string attached, placing the ball at the end of the line of books. My idea was for the books to knock into the ball, setting the pendulum into action.

Finally, I had to figure out how to use the mousetrap. I decided the mousetrap would be the easiest way to pop the balloon because of its high potential energy which is quickly realeased. In order to trigger the mousetrap, I added another few dominoes near it that would be knocked over by the pendulum. To pop the balloon, I added a wooden stick to the side of the trap, which would swing around and slam against the balloon. The first time I tried it the balloon wouldn’t pop, so I added another spike to the stick to pierce it.

After many runs, multiple adjustments, and so much time setting up dominoes, I had recorded a perfect run.

ENERGY CALCULATIONS

Marble down PVC pipe (LoggerPro)

Mass of marble: 0.005 kg

Initial height: 0.162 m

Velocity of ball after run: 1.568 m/s

PE = mgh = 0.005(9.8)(0.162) = 0.0079 J

KE = (1/2)mv² + (2/5)Iw² = (1/2)mv² + (2/5)mR²(v²/R²) = (7/10)mv²

KE = (7/10)(0.005)(1.568)² = 0.0086 J

PE was converted to KE, with a small margin of error.

2. Rubber ball down track (hand calc, friction ignored)

Mass of ball: 0.247 kg

Initial height: 0.04 m

PE i = KE f

PE = mgh = (0.247)(0.04)(9.8) = 0.097 J

KE f = 0.097 J

3. Pendulum (hand calc, friction ignored)

Mass of ball: 0.023 kg

Initial height: 0.08 m

Final height: 0.025 m

PE i = mgh = (.023)(9.8)(.08) = .018 J

PE f = mgh = (.023)(9.8)(.025) = .007 J

PE f - PE i = KE f = .011 J

4. Mousetrap (LoggerPro)

Angle = π

PE i= integral(Tdθ) = Area under curve at θ = [0, 3.14] = 10.08 J

KE f - PE i= 0

KE f= 10.08 J