## Introduction: Earth Day Piggy Bank + Geometry

Sometimes we throw away a lot of garbage that can be used to create something useful. A piggy bank made out of glass can be hard to maintain and use. A piggy ban made out of an empty milk jug is easy to make, easily decorated, and everything you need to create is probably in your house right now. If you throw away or recycle your empty milk jugs, you can use them to store your savings or loose change to exchange later. Some people don't like keeping excessive amounts of change in their wallets.

We are going to use volume to find around how many pennies can be stored in one empty milk jug.

## Step 1: Finding the Volume of a Penny

Through research we found out that the volume of one penny is about .36 cubic cm. This is rounded to the nearest hundredth.

The formula for volume is (surface area of 1 face) x (height), so in the case of the penny with a circular face, we can say the formula of the penny is (pi) x (radius^2) x (height).

Volume= 3.14 x 9.5 x 9.5 x 1.27

= 360 cubic mm or .360 cubic cm

## Step 2: Converting Measurements to Liters

Again, the volume of a single penny is .36 cubic cm. We are going to convert this number into liters because it is more proportional to gallons.

There are 1000 cubic cm in one liter, so our conversion would become .00036 L.

Therefore, if one penny is .00036 L, and 1 L is divided by .00036 L per penny, then one liter should hold 2777.7 pennies.

## Step 3: Converting Measurements to Gallons

Through a unit converter, we found out that there are 4.405 L per dry gallon. We are using dry measurements because the pennies are solid but the jug uses liquid measurements (gallon).

2777.7 pennies per liter x 4.405 liters per dry gallon

= 12236 pennies

This amount of pennies is assuming that the jug is packed to the brim and it is totally filled with pennies. But pennies have an irrregular shape and they aren't liquid, so there will be about 25% (roughly) air space between the pennies.

12236 pennies x 25% = 9176 pennies

## Step 4: Additional Ideas

If you plan to go along with our milk jug piggy bank idea, you could keep saving up coins for donating or personal use. Keeping them in a closet or a cabinet could be more convenient than having them out in the open. This could also be a fun project to do with your children or a child you know. Decorating them will make it more valuable and you and your friend could watch as the coins add up over time.

Cut a slit in the cap to make your bank, and you're pretty much done. Open the cap to retrieve your money more efficiently when the jug is full.

You can customize and decorate the jugs to your liking, too.

## Step 5: Our Philosophy

People don't usually think twice about the milk jugs that they throw away. Those milk jugs end up in landfills and build up over time which isn't good for the environment because plastic can take centuries to decompose into the ground. This is a disadvantage due to the fact that the soil on the ground would benefit greatly from added nutrients making richer soil for plants to grow some day. Saving the bottles can help a ton and will make a difference if everyone works together to save the Earth's health and beauty.

## Step 6: Repeating the Steps With a Nickel

The formula for volume is (surface area of 1 face) x (height), so in the case of the nickel with a circular face, we can say the formula of the nickel is (pi) x (radius^2) x (height).

3.14 x 1.05^2 cm x .17 cm

=.59 cm^3 or converted into an appropriate unit, .59 mL.

Using a unit converter, we found out that .59 mL = 0.00059 L

Therefore, if one nickel is 0.00059 L, and 1 L is divided by 0.00059 L per nickel, then one liter should hold about 1694 nickels.

Through a unit converter, we found out that there are 4.405 L per dry gallon. We are using dry measurements because the nickels are solid but the jug uses liquid measurements (gallon).

1694 nickels per liter x 4.405 liters per dry gallon

=7466 nickels

This amount of nickels is assuming that the jug is packed to the brim and it is totally filled with nickels. But nickels have an irrregular shape and they aren't liquid, so there will be about 25% (roughly) air space between the nickels.

7466 nickels x .25% air= 1866 nickels

## Step 7: Repeating the Steps With a Dime

The formula for volume is (surface area of 1 face) x (height), so in the case of the nickel with a circular face, we can say the formula of the nickel is (pi) x (radius^2) x (height).

3.14 x 0.895 cm^2 x 0.135 cm

=0.34 cm^3

Participated in the

Instructables Green Design Contest

## Comments

8 years ago on Introduction

This instructable was really well done and put together. You emphasized the math very well and have proven your point. Good work.