Comments | tacotortoise: Pennies to Heaven

tacotortoise

Pennies to Heaven

Jan 23, 2006 20:07

So...penguinkraft's mom gave her a bunch of glass jars, against her will. Many of them have an old-timey apothecary feel, and have been repurposed as canisters for flour, sugar, and other baking supplies. The largest one, though, has sat empty for most of its time here. It was clearly meant to hold bagels or some other baked goods, but we never really had ( Read more... )

geekery, roommates

Comments 4

Another way zandperl January 23 2006, 18:09:38 UTC

As I like to tell my students, there's always at least one other way to solve a problem. Often two other ways.

In addition to having a mass of 2.5 g, a penny also has a diameter of 19.05 mm and a thickness of 1.55 mm. Assuming you need 3,675 pennies, and that because of funny stacking, up to 1/3 of the volume will be empty space, that'd be 2.435*103 cm3.

To double check your work, divide the mass you got by the volume I got, and you should get a density less than that of zinc (pennies' main component), which is 7.140 g/cm3 - specifically I would expect 2/3 of that value since I assumed 1/3 of the space is nearly massless air, so I'd expect 4.76 g/cm3. I get a value of 4.285 g/cm3, meaning your number for the mass is consistent with my work.

Now that we have a target volume of pennies, it is trivial for you to determine the height to which the jar will need to be filled, and it is a much easier quantity to measure than the mass, considering your scale. Unless you really want come up with a pulley system by which the force ( ... )

Re: Another way tacotortoise January 23 2006, 18:48:14 UTC

We have considered a volumetric approach as well. The problems of filling space make it less accurate, ignoring the difficulties we have had with wighing things. The best way to do this, in my opinion:

* Take a known, but reasonably large, quanitity of pennies. Maybe the pennies that are already in the jar, should I choose to count them.

* Put them in an appropriately-sized container, and measure the volume they occupy, including empty space.

* Scale up appropriately.

Re: Another way zandperl January 23 2006, 18:51:55 UTC

You could weigh the current amount of pennies and use that to determine the number, and therefore the density.

Re: Another way tacotortoise January 24 2006, 09:14:53 UTC

Weigh? We've already been down that road.