Bargains galore

I've been shopping on eBay again. This time I managed to buy two Vernier labPro interfaces with motion sensors and a bunch of wires that on closer inspection look like they include a temp. probe and a voltage sensor.  Also included are two PH meters, I'll probably give those to the chemistry dept. to thank them for all the bits of tubing and rubber bungs that they don't know they've given me in the past. There were actually 4 sets but I didn't want to be greedy. They cost £60 each which is incredibly cheap. Have to add something on for postage and tax when the enter Norway, but they were still too much of a bargain to miss.

So, now I've got to work out what to do with my new purchases. With the other LabPro and motion sensors I got from eBay earlier in the year and the two had already I've got a class set so need to think of a class practical. I'm doing Forces with my first years at the moment so thought it might be an idea to do something with air resistance. The classic practical uses those big frilly coffee filter but my local shop didn't stock them so I thought I'd try balloons. According to Stoke's law F=6πηvr. When the balloon reaches terminal velocity mg = F = 6πηvr so v should be proportional to 1/r. I did a quick experiment to see if this is true and got some quite a good straight line when plotting v vs 1/d. I think I'll create a worksheet later in the week.

Here it is: Balloon Drop

I've also ordered some coffee filters from eBay so will be able to try that one out soon as well.