Setup of the Quantitative Description of Your Rube Goldberg Device Step

Milestone 2 Guidance For your final project… Most important…. KEEP IT SIMPLE

• Thank about the equations you are most comfortable with when it comes to calculating velocities and energy transfer. Build your device around those situations.

• Start with a pencil sketch!

• Use at least three steps. Your “selected step” for analysis cannot be your first or last step because you need to analyze the transitions before and after your selected step.

Example:

The only time the initial velocity is zero is if gravity starts the step’s motion. If there is any sort of interaction between two objects, the initial velocity of the step is the velocity of the object AFTER that interaction. In the above example, the red ball is at rest when the blue ball starts. The selected step, though, starts with the velocity that the red ball has picked up from the interaction with the blue ball. Any transition that involves contact with moving objects will have a transfer of energy. For an object that flips a switch and releases a ball allowing gravity to act on it, there is work done to flip the switch, but no energy transferred to the next step. For Milestone Two, if you chose the step that you will analyze for your final project, you can use the work you do for Milestone Two and my feedback to make it all perfect for the final submission. For Part 1 of this milestone, you will describe the selected step.

For Part 2 of Milestone 2, we look to the transition between the previous step and the selected step:

This section has three parts. First, describe in words what is happening between the two objects at the transition and how the energy is being transferred. This is just to set the stage, do not include equations and numbers in this intro section. The second part is to introduce the equations you will be using to track the energy and momentum. Conservation of momentum tells us that the total momentum before the collision will equal that total momentum after the collision. Conservation of energy tells us that the total kinetic energy before the collision is equal to the total kinetic energy after the collision. The trick is to write the equations to match those two scenarios. The assignment also asks you to explain “the connection between the basic physics concepts in the equations and the interaction of the object and force(s) from step to step.” That means you need to explain what numbers you will plug into the equations, where you will find them and what you will solve for. The final part of this section is to perform the calculations and describe how those numbers indicate the future path of the object in the selected step. In Part 3 of Milestone 2, we look at how the energy distribution changes throughout the course of the selected step:

We are looking at the changes in kinetic and potential energy as the ball travels through the selected step. The total energy remains constant throughout the step. This example has changes in height, which means changes in potential and kinetic energy. Your selected step might not have changes in height, which means

you will not have any changes in how the energy is distributed. If that is the case, be sure to explain why there is no change in energy… don’t just skip this part of the milestone! For Part 4 of Milestone 2, we go through the exact same process as we did for Part 2, but we use the transition to the subsequent step for our analysis.

When I set up my scene, I double clicked (right click on a PC) on the blue ball and looked for the VELOCITY option. I set the initial velocity to 3.5 m/sec to kick off the interaction. In the MATERIALS option, I set the friction to zero and the restitution to one. A restitution of one is what makes the collisions elastic and zero friction will give us constant energy throughout the motion. After that, I clicked on all objects and surfaces one at a time to make those same friction and restitution settings. Most of all, have fun with it!! Try not to overthink it. Review the project guidelines again after you finish writing your project and use the checklist below to make sure it is complete:

 Part I: Description of selected step

 Part II A: Description of transfer of energy through the interaction between previous and selected step. What do you know about energy and momentum?

 Part II B: Provide equations you will use to describe energy and momentum transfer between steps. Also indicate what you will measure and what you will solve for.

 Part II C: Perform calculations. Show all work and include standard units.

 Part III A and B: Provide equations to calculate changes in energy throughout the step, then perform the calculations showing all work and using standard units. If there are no energy changes, explain why the energy does not change. DO NOT SKIP THIS PART

 Part IV A: Description of transfer of energy through the interaction between selected and subsequent step. What do you know about energy and momentum?

 Part IV B: Provide equations you will use to describe energy and momentum transfer between steps. Also indicate what you will measure and what you will solve for.

 Part IV C: Perform calculations. Show all work and include standard units. You can also use the project rubric to ensure each section has the required amount of detail.