Day 115: Bag and Tag

Today is the infamous bag-and-tag day for the FIRST Robotics Competition. For the past six weeks and three days, students have been obsessed with designing, building, and testing this year’s robot, Annie, for the Aerial Assist game. By midnight, the robot must be sealed in a large plastic bag and secured with a security tag. Despite having Annie bagged, we will continue to work just as hard over the next two weeks until our first competition at the Lake Superior Regional in Duluth, MN. I’ll share more details of Annie later as the media team is busy working on the photos and videos. The bag was sealed at 11:57 pm!

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Day 114: Raku Pottery

My colleague has arranged for a special project for our Honors Physics classes. Over the next couple of months, they will have the opportunity to craft a ceramic piece and have it fired in the Raku process. To introduce the project we shared several examples made by a student in a previous year. I have three students in my class who have taken ceramics which will make it easier to manage this project since I know little. Really looking forward to this practical application of rotational motion!

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  ##rotationalmotion ##practicumlab  

Day 113: Moment of Inertia Lab

Today’s lab we are doing as a whole class in more of an interactive lecture demonstration format. The apparatus, procedure, and analysis are somewhat involved and I want to ensure that each student understands each step along the way. The purpose is to experimentally determine the moment of inertia of a solid disc and a ring. We will do this by first determining the angular acceleration of the system by graphing angular velocity vs. time. We will then determine the moment of inertia of the system by graphing applied torque vs. angular acceleration. We have to first determine the moment of the apparatus so we can subtract that from the moment of the disc and ring. There is a great opportunity for a side discussion of how the vertical intercept of the torque vs. angular acceleration graph is the torque due to friction in the bearing.

The data we collected in class looked good, but the experimental results show a moment of inertia ten times greater than what is calculated using the mass and geometry of the disc. We haven’t figured out what the problem is. We did realize that we weren’t accounting for the acceleration of the mass hanger and, therefore, the tension in the string is less than the force of gravity. However, I fixed that, and it had minimal impact on the results. If anyone sees a flaw in the experimental design, please let me know!

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  ##setbacks ##paradigmlab ##expdesign ##rotationalmotion  

Day 112: Moment of Inertia Demonstrations

We are exploring moment of inertia from several different perspectives. We’ve felt it experientially, derived equations mathematically, observed its effects, and will measure it experimentally. Today, I performed a simple demonstration of rolling two wheels of equal size and mass but different mass distribution down a slight incline. The wheels experience the same torque and yet clearly accelerate at different rates. It is a simple, but convincing demonstration of the effect of the moment of inertia of an object.

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  ##demos ##rotationalmotion  

Day 111: Business Partnership Breakfast

This morning I was at school at 5:30am to prepare for the school district’s Business Partnership Breakfast. I was proud to attend with my colleagues and three students from Huskie Robotics, FIRST Team 3061. We and our partnership with Navistar were being recognized. While addressing those in attendance, I focused on the mission of FIRST and how business partnerships go beyond the financial support that allows us to participate and be competitive and connect employees to students through mentoring. One of the students then shared her experience working with various mentors at Navistar. She did a fantastic job. We ended our presentation with a brief demonstration of last year’s robot. Since last year’s game involved frisbees, the distribute gave everyone in attendance a “business partnership” frisbee to take home!

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Day 110: Rotational Equilibrium (Balanced Torques)

Today students practiced analyzing a system in rotational equilibrium. We had them hang two masses on the stick and calculate where a third mass should be placed such that the meter stick would be balanced. We then had students hang an object of unknown mass and calculate its mass. This was good practice for calculating torques. It was also good practice for their upcoming lab practicum. Throughout the activity, students discovered that the system would be more stable if the bracket at the center of the meter was oriented such that the screw was facing downward. Several pairs were surprised at the inaccuracy of their prediction until they realized that they didn’t account for the mass (and torque) of the mass hangers. One common thought among students was that the mass of the mass hangers didn’t matter since all objects were hung from similar mass hangers. I let them think about this for a few seconds until they realized that each mass hanger had a different length lever arm!

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  ##paradigmlab ##rotationalmotion