The Light Bulb! 4/26/09. By: Heather Boynce, Chanci King, and Austin Graham. Heather: Power Point and Calculations. Chanci: Design and Calculations

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1 The Light Bulb! 4/26/09 By: Heather Boynce, Chanci King, and Austin Graham Heather: Power Point and Calculations Chanci: Design and Calculations Austin: Construction and Testing We all approve of the report and all aspects of the project.

2 Abstract: We built an overly-complicated device that goes through a series of steps and includes such concepts as; conservation of energy, conservation of momentum, rotational energy, torque, and center of mass. We built our device to be a visual display of concepts we have learned this semester. By working together, using materials we could find, and applying the concepts mentioned before, we were able to build a Rube Goldberg device which can be used to turn on a light bulb. ii

3 Introduction: In this project we were required to use the concept we learned this semester in class to put together a Rube Goldberg device. This is a device that has many steps to operate a simple electrical device. This device had to include at least four concepts we went over in EF 151 this semester and it had to go through at least five steps. Description of design process: We started our project with the idea of what concepts had to be included. We knew we would have to have a device that would have to have plenty of stored energy as well as go through at least five steps to turn on some form of electrical device. We decided the best form of electrical device to use would be something with a switch rather than a button. This way we could tie something to a switch rather than having to worry about something landing on a button every time. For this reason we decided to use a light bulb with a pull switch. We also knew that we had to include at least four concepts that we have learned throughout the semester. We decided the best four to use in our project were conservation of energy, conservation of momentum, center of mass, and torque. We decided the best way to show conservation of energy would be to start a ball, this way we would also be including rotational kinetic energy, at a height and roll down a ramp. In order to include conservation of momentum we knew we would need to include some sort of collision. We decided an elastic collision would be best. Then we had to consider how to use center of mass. We decided to do this with a balance. Finally, we had to find a way to incorporate torque; we decided to do this using a lever that fell onto a mouse trap. The lever has

4 torque because it rotates about a pivot. Our last step, we decided that a mouse trap would be the best way to pull the string that would turn on the light. Description of Device We decided to start our device off with a golf ball at an initial height giving it potential energy. Then in order to include the concept of conservation of momentum we had the ball roll down the ramp gaining kinetic energy and rotational kinetic energy and then colliding with a block of wood that was initially at rest. When the block is moved by the golf ball it pulls a string which is attached to a wood peg. It pulls the peg out of a PVC pipe that is placed about 19 inches above the ground. This then releases a tennis ball that had originally been held at rest by the wooden peg to roll down a pipe gaining kinetic and rotational energy. The tennis ball then drops onto a balanced piece of wood with some velocity, which throws off the center of mass of the wood balance and causes the wood balance to tilt pulling another piece of string. The other end of that string is tied to a wooden peg holding a wooden lever up which contains potential energy initially. The wooden lever then falls onto a mouse trap with a certain force causing it to snap and pull a string. When that string is pulled it then turns on a light bulb. All the materials that we used in our project we found around our homes, therefore we did not have to buy any supplies. Results of Testing: When we ran our device for the class the first time the ball had too much velocity and missed the balanced wood. We then relocated the piece of balanced wood so that the ball landed on it and the device worked turning on the light bulb.

5 Conclusions: During this project, we incorporated what we learned this semester using calculations and concepts from class to build our very own overly-complicated device. Throughout the process we ran into problems with the ball landing on the balance. We could have been more successful if we conducted further testing and found a way for our device to be more consistent. References: We used notes and equations provided to us from lectures. Calculations: Conservation Of Momentum (Collision) mgh = ½ m v 2 + mgh + ½ I ω 2 (.0457 kg)(9.81)(19 in.) = (1/2)(.0457 kg)v 2 + (1/2)((2/3)(.0457 kg))v 2 V = in. / s mv ball = mv ball + mv wood (.0457 kg)( in/sec) = (.0457 kg)v ball + (.07)v wood V ball v wood = -(v ball v wood ) ( in/sec) 0 = -v ball +v wood Solve for one variable in both equations and then set them equal to each other then solve.

6 v ball = in/s and v wood = in/s in/s in/sec in/s Conservation Of Energy (with rotation) mgh = ½ m v 2 + mgh + ½ I ω 2 (.056 kg)(9.81)(2.5 in.) = (1/2)(.065 kg)v 2 + (1/2)((2/3)(.056 kg))v 2 V = in / s 2.5 in in/s Torque (Rotational Motion) τ = F r sinѳ τ = (.032 kg)(9.81)(12 3 / 8 in.)sin( ) τ = N-in.

7 2.649 N-in in. Center Of Mass We had a symmetrical piece of wood and found the center of mass so that it would balance on another piece of wood. When the tennis ball was projected onto that balanced piece of wood it threw off its center of mass and began to tilt. We then placed a wooden rod on the end the ball was projected onto so that it could counteract that weight and the ball would roll the other direction and the now unbalanced piece of wood tilt the other desired direction. CM = (mr/m) = ( in./2) = in. in the x direction = (3 in./2)= 1.5 in. in the y direction X= in. Y= 1.5 in.