2/16 Tuazon

Quick stuff to know:
- Turned in: Nothing
- Returned: Energy test
- Assignments made: Finish Crazy Coasters calculations (Plus working on your group's windmill or Rube Goldberg machine)


Detailed stuff:
I walked into my second class period on this fine February the 16th of the year 2012 thinking about how I was going to prepare for yet another gathering-info-to-write-my-blog-with session. Then I forgot all about it two seconds later.


No matter. My memory will serve me well.


So on that fine, fine day, after my short term memory threw out the thoughts of my blog, we picked up our Energy Test from our folders. 


We began the class period with Coats-Haan and Mr. Ebersole asking us what were some good ways and bad ways of measuring the exit velocity of the marble as it left our rollercoasters. Two good ways were to use one of the photogates around the room (which Coats-Haan shows us how to use) and to measure it using the 3rd kinematics equation and the distance that the marble travels from being ejected at table height until it hits the ground. (I detail both of the good methods in my answer to the QotD.) One of the bad ways included using timers because they would be unreliable due to the great amount of human error involved in stopping and starting the them. Using Ui + Ki = Uf + Kf could also be considered a bad way because even though it gives a ballpark exit velocity, it does not take friction into consideration. 


Afterwards, Mr. Ebersole dismissed us from our tables so we could continue working on our ever-so-innovative rollercoasters and so we could experimentally measure the exit velocity using the two good methods. 


Matt's group had to finish putting their through-the-cardboard rollercoaster together. It was actually beginning to look sort of bulky and intimidating with all the tubing and double cardboard panels everywhere. It was like a Franken-coaster. However, Coats-Haan and Mr. Ebersole did say that many other groups throughout the day were copying their raging through-the-cardboard design. Good for them, setting precedents and whatnot. 


Back at our overly duck-taped, one-loop wonder, Trevor, Chris, Aimee and I went straight for the photogate at the end of the room to measure our exit velocity. It took us a while, though. Sometimes, because the beginning of our track was so steep, the marble would not land on the track until a second or two later and the marble would have an usually slow exit velocity from not being able to pick up the full speed from the tubing. Much of our time was spent stacking and removing Chris' folders and trying to get the photogate to sense that the marble was passing through it. Late we realized that the marble was simply shooting out a little too high for the photogate to sense it, and we all mentally smacked ourselves in the faces. 


Measuring with the 3rd kinematics equation method was a little more eventful. We propped our rollercoaster board up on top of Mr. Ebersole's table back by the AP lab, and after we measured the height of the table (0.8 m), we had a great time trying to see if the marble would land in the same spot every time (this is not a necessary step to finding the exit velocity). After our initial marble release, Chris put his eraser approximately where the marble landed (about .9 m away in the x-direction from the end of the rollercoaster) and we continued putting the marble through the coaster to see how often the marble would land in the area around the eraser. 


To end the period, we relaxed and finished our final calculations on the Crazy Coasters worksheet. 


Note: For #13, when you use the 3rd kinematics equation, use a height of 4 m instead of the 4.6 m (a measurement which has been wrong for years, apparently). The time you get as your answer in #13 will be used in the 3rd kinematics equation as well for #14. 


Question of the Day: 
Q: How do you measure exit velocity with the photogate timer?  How do you measure it by projecting it off the table?


A: To measure exit velocity with the photogate timer, you take the diameter of the ball and divide it by the change in time from the moment the ball entered the photogate to the moment it left the photogate. 


To measure the exit velocity by projecting the ball off the table, you use the 3rd kinematics equation for the motion in the y-direction to solve for the time it takes to touch the ground. You then take the distance in the x-direction that the ball traveled and divide it by the time you found using the 3rd kinematics equation to get the exit velocity. 


End Blog.


(Not too shabby for not remembering it until now, eh?)