Archive for February 2012
Good Intentions, Bad Lab
Posted on: February 28, 2012
A couple of weeks ago we did a lab straight from the textbook. (Here is the Lab Instructions, typed up and put it into my words.) I’d been looking for a good Conservation of Energy Lab. I wanted to use the Vernier devices, but there wasn’t anything in their book that I liked. Rather than make something up from scratch, I decided to work directly from the Holt Physics textbook.
The lab had two parts; the first was to calculate the spring force constant using a Hooke’s Law device. I didn’t have that device, so I created my own by first designing a simple indicator on Solidworks (3D CAD Software) and then printing eight of them in the 3D printer. That worked out great. (I will try to remember to post my Hooke’s device design, you can build them for about $0.25 each.) Unfortunately, it was the only part of the lab that worked out at all.
We were able to use a ring stand, ruler, and indicator to successfully calculate the spring force constant. The second part of the lab was supposed to demonstrate conservation of mechanical energy by bouncing the weight and measuring the high and low point. Quite honestly, it just didn’t make sense. At first it did, but the more I thought about it, the less sense it made.
To begin with, it was nearly impossible to measure the bottom and top of the bounce with any accuracy. It was pure guesswork and the kids were really struggling.
This is a great bunch of kids, I warned them ahead of time that this was the first time using this lab, there might be some hiccups. They were understanding and really tried to make this work, but they were totally frustrated. I told them I would grade the lab on their effort, spring constant results, qualitative analysis, and attempt at explaining the results.
Clearly, I need a much better lab for next year. I was originally thinking of calculating the spring force constant, then determining the weight of an unknown object based on distance the spring stretches. That makes sense for the chapter on oscillations, but not for Conservation of Mechanical Energy. I don’t have an air track, but I’m really good at McGuyvering solutions, as you all well know.
Please throw your awesome labs my way, I need help.
The Last Three Robot Challenges
Posted on: February 6, 2012
- In: Engineering | Robots
- 5 Comments
The last three challenges of the LEGO portion of our show are:
#3 – Ribbon Climb
#2 – Battle Bots
and #1 – Inventorying the kits for next year.
Sorry for the trick, but we started trying to put the kits back in order. Most weren’t done after a full hour. All the groups have both a standard kit and a blue resource kit. They were under orders not to borrow or loan to other groups. That didn’t happen. I needed the basic kits back in shape so the students next year can build the basic robot that we use for the first couple of months. The kits are a complete mess.
One trick I came up with from my manufacturing days… I made photocopies of the groups of parts. The student place the identical parts on their picture. When the sheet is full, they deposit that sheet’s parts into the assigned storage location. So simple a child can do it, or hopefully a high school senior.
On to the ribbon climb. This was a variation of the rope climb, but the kids liked it a lot more. The ribbon was a 7 foot-high, 3 inch-wide strip of manila folder that was covered on all sides with duct tape. The folder gave it rigidity so that it could stay within edge guides. The tape gave us protection from massive paper cuts and also provided a higher friction surface.
I educated the kids on the use of gears and mechanical advantage. Some of them listened and their robots carried between 0.5 and 1.5 kg of additional weight up a ribbon.
The actual last challenge was Battle Bots. The rules quickly morphed into the following, and it was a major hit.
- Teams can battle every robot once a day for points. I had to witness the point battles for it to count. Teams can battle as often as they want, just not for points.
- Robots can only be built with the parts in their two kits. No outside materials are allowed.
- You win by flipping your opponent’s robot over or pushing it out of the arena. (Nobody got pushed out, the wall were too high – there will be lower walls next year.)
- The battle goes one minute. If at the end of a minute, there is no winner, both teams get one point. If there is a winner, the winner gets 3 points, the loser gets 1 point.
- You win by accumulating the most points over the period of 5 days.
This got them battling right away. The robots were constantly improved and new strategies were tried. In the end, there can be only one.
Physics & Physical Science Demos, Labs, & Projects for High School Teachers 
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