Today, I demonstrated an extreme example of an unbalanced force acting on an object with our ping pong ball cannon. My colleague created a great problem which my students will solve tomorrow:
We can estimate the speed of the ping pong ball from yesterday’s demo with the help of some background information, some guesstimates, some assumptions, and a little physics. The ball has a mass of 2.7g, assuming a full vacuum of 101,325 Pascals, and cross-sectional area of the ball of 1.26×10-3 m2. The result is approximately 127.6 N of force pushing the ball inside the 10-ft long tube. Draw a free body diagram of the ball in the tube, and estimate its acceleration. Then sketch the beginning and ending conditions of the ball, including all variables and find its exit speed in mph (pay close attention to ALL units). o you think the ping pong ball was actually going this fast? Why or why not?
Here’s what it did to my soda can.
Tonight, I submitted my application to be part of the 6-12 Science Curriculum Committee. With our new career management web application, I had to request approval to submit the application, but we’ll save that story for another day. I probably got a bit carried away in my application, but I take these efforts seriously. I’m not going to share my entire application since that would be too self promotional. However, I do want to share part of my answer to the prompt “Explain why you feel you can represent your grade level/content area/building colleagues in this work.”
… Most importantly I’m not afraid. I’m not afraid to ask questions; I’m not afraid to call anyone out; I’m not afraid of what people think of me; I’m not afraid to look stupid; I’m not afraid to learn new things; I’m not afraid to take risks; I’m not afraid to fail; I’m not afraid to throw it all out and start again; I’m not afraid to work hard. I’m not afraid of change.
I missed last Friday. I went to the crosstown football game against our sister school but forgot to take a picture. Today, we started the unbalanced forces particle model in Honors Physics. Our paradigm lab is the modified Atwood machine. Since this is the first lab with multiple independent variables and given the complexity of the how to keep the system mass constant while changing the net force, we spent most of class discussing and planning the lab.
This year, we tried a new lab practicum for the constant-acceleration particle model unit. I don’t think we came up with on our own, but I don’t remember where I saw it. Students are presented with a constant-velocity buggy, a ramp, and a marble. They have to mathematically and graphically model the motion of the buggy and marble as it rolls down the ramp. After they have created their models, I provide them with a displacement for the buggy perpendicular to the end of the ramp. They then calculate from where to release the marble such that it rolls into the seat of the buggy.
Based on my observations of my class today as they worked on the lab, I was very surprised when most groups missed the buggy entirely. Only after checking over their calculations after school did I realize that most groups made the same mistake. They incorrectly interpreted the slope of their linearized position vs. time squared graph as the acceleration of the marble when, in fact, the slope is one-half the acceleration of the marble. They then used this incorrect value of the acceleration to calculate the initial displacement of the marble.
We now have something to discuss tomorrow.
##capm ##practicumlab ##setbacks