At this year's AP reading, I was pointed toward dealextreme.com, a Big Lots style online retailer. You can't rely on them to have exactly what you want, but if they do have what you want, it will be cheap.
When I browsed the site last month I found some "portable electronic scales," pictured to the right. Huh... I use crappy spring scales that are easy to break. My set is in need of replacement.
This electronic hook scale doesn't measure in newtons, but does in kilograms (or ounces or pounds or "Jin," whatever those are). The range is up to 20 kg -- way more than I ever need -- and has a 10 g resolution.
Dealextreme sells these for 6.90 apiece, with free shipping. That's much less than I paid for crappy spring scales from a major science supplier last year.
The reader who recommended dealextreme.com warned me to order one of anything before I buy a class set. He said that sometimes the products are defective or just lousy. But because they're so cheap, it's worth the occasional lemon. I bought two of these portable spring scales, and both work fine. I'll set up my opening demonstration next week using these rather than spring scales; I ordered eight more so I'll have a class set for our first laboratory exercise.
Oh, and if these do die in a year, they are no worse than what I ordered from Fischer or Flynn or Sargent-Welch.
So resolution of 10g with 20kg range. What about accuracy? Did you try measuring any known masses? Is the 10g resolution comparable to the accuracy or are they 5% of full scale (±1kg)? Cheap digital products often have resolution that is much better than the accuracy, which can mislead students badly if they don't get instruction in determining the accuracy of their measuring tools.
ReplyDeleteI'm homeschooling my son in physics this year and looking for cheap lab equipment, so this looks promising.
The ones I checked were accurate within the .01-0.20 kg range. I haven't checked higher masses yet, but I'll let you know when I have the chance. The range up to about 300 g is what I'm really looking for.
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