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Electrostatic attraction
Above is an experiment being done on the International Space Station. It shows water droplets being attracted to a charged knitting needle (similar to how you can use a charged rod to attract a aluminum can in your lab this week). When watching this I want you to ask yourself if the droplets need to be charged to be attracted to the needle. If you remember class we found that a charged object can induce charges in a neutral object and then attract it. In fact this is what is happening here. So don't listen too carefully to the explanation in the video. One of your instructors (KM) became irritated that this phenomenon is often explained incorrectly. Many places claim that charged objects induce a net charge on water droplets and this leads to thier attraction. But this is incorrect. In order to test this I repeated the experiment with insulating oil so that no net induced charge could arise. Instead the polar molecules in the water (or oil) line up, resulting in the atraction just like the charged balloon attracting the wall in class. Here's a link to that experiment: Electrostatic attraction with water/oil
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Announcements
- Written Homework #2: Due Friday Sept 21, at 2 PM. (See Homework link on the left for details)
- Desire to Learn: We have a D2L site, please visit it. We will be putting up homework solutions and grades there. A couple of people are using the "Discussion Forum" for homework help - that only works well if lots of people use it, so please join in! (And, don't forget to look at our "virtual office hours" link on occasion. If we get homework questions by email, sometimes the response goes up there)
- Written Homework #1: Due to the holiday Monday, written HW#1 is now due Monday Sept. 10th at 2pm. This is a one time deal (unless you can get more federal holidays inserted into the schedule!). Note the time and special date and turn them into the box in the front of the help room. Please put it in the correct box for your TA!
- CAPA #4 is due Wed Sept 19 (#3 Sept 12, #2 is due Wed Sept 5 ). Printed versions are in the usual place in the basement 2B just outside the help room. If you can't find your copy use the PIN getter on the CAPA website http://capa-new.colorado.edu/capa-bin/classsbin
- Don't forget to do your Prelab and print our a copy of both it and your lab before your section.
- There is a weekly optional review session run by Ariel Paul, every Tues at 8 PM, in G125 (1 floor up from our class) You can go there to talk about any questions, homework, etc. He'll even be there the first week! Exam weeks, we'll add an extra session Wed too - stay tuned.
- REGISTER TO VOTE in the upcoming elections at STUDENTVOTE.ORG!
The best way to get political leaders to pay attention to you is to register and vote this November. COPIRG’s New Voters Project is a non-partisan effort to make sure every student at CU Boulder gets a chance to do just that. You can register to vote online by going to StudentVote.org and following the instructions.
Alternatively, you can go directly to the Colorado state gov't website (which has more voter information as well as registration information) at http://www.sos.state.co.us/pubs/elections/vote/VoterHome.html
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The previous homepage and announcements can be found here: week #1