Physics & Physical Science Demos, Labs, & Projects for High School Teachers

Homemade Hooked Masses

Posted on: May 26, 2011


I needed unknown masses for my Torque Lab.  Good thing I don’t seem to ever throw anything away.  I’ve been taking Prevacid for about a year now, it comes in a really handy sized bottle.  (Now let me just say, if you have a chronic indigestion problem and you don’t try this or one of the other drugs like Prevacid, you are missing a life changing drug… seriously.)  Anyway, these cool little bottles tend to stack up rather quickly.  I took a small screw hook and tried to put it into the top but found it difficult to center it and drilling was too much work.  Instead, I turned the bottle upside-down and inserted the screw hook into the bottom of the bottle.  This worked great and I like the look.  By changing the contents to lead, I can make these much heavier.

I wanted to put lead shot in the bottles, but I didn’t have any.  I was going to purchase fishing weights, but for what they cost I decided to just use pennies.  They are mostly copper, fairly dense, and I can fill a bottle for about 20 cents.  It turned out to be cheaper to use money as a weight than to spend money to buy anything else.  In some of the bottles I put odd screws and other metal bits to increase the density.  I made sure none of the masses were at even values, and they are all different values.  In other words, the mass of one bottle was 87.2 grams, not 80.0 grams or 85.0 grams.  For some reason, my students believe all answers should be whole numbers.  Of course I don’t believe that.  I numbered the masses #1-#12, weighed them on my gram scale, and recorded their mass on a note card and stored it in my desk drawer.  During the lab, I refused to tell them the values of their unknown masses, and my gram scale was locked up, but I did tell them their answers should be in the range of 75 to 120 grams.  I did find the unknown weights would work better if they were more in the range of 150 g.  I’ll have to see what lead shot costs, maybe a bag of it is in my future.

During the lab, I instructed the students to make note in their lab notebook of which unknown mass they used during the lab.  I explained that each mass was different and they needed to stick with the same one each day.  Despite the explanation, about half the groups didn’t make note of which unknown mass they used.  Some of them just said it was white.  Well, at least we have colors down.

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5 Responses to "Homemade Hooked Masses"

awesome! Why are unknown masses that can be hung on springs or torque hooks so hard to find/make? I seem to be forever trying to find unknowns to use. Finding unknowns, in torque, on masses on a spring, are great labs.

I have taken washers and strung them on a string, then tied it together, to make a loop of washers. They seem fairly heavy and work ok. But I like your bottle idea. Pennies are great and cheap!

We are flinging loonies in 2 weeks on catapults – uniform, and cheap masses. (Loonies – Canadian dollar coins)

This seems silly, but because the bottles are upside-down, the kids don’t tend to open them. The weights I made that are right-side-up, they open as soon as they touch them. Isn’t that odd?

That’s an awesome idea. I always get frustrated because we don’t have standard masses easily available at my school, but I never want to use precious budget to buy more. This is a great idea and I’ll be using it from now on.
Thanks!

I’ve done something similar with old 35mm film canisters and BB’s. If you go to a photo processing place, they probably have a bunch of film canisters that they would otherwise send to recycle or throw away. I asked at a Walgreens and they were more than happy to give me a teaching career’s worth of film canisters.

great idea! Thank You!

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