Eventmath/Lesson plans/Dimensional analysis, shipping, and an impossible weight limit

Activities
Given information
 * Box dimensions: Length = 8 5/8 in, Width = 5 3/8 in, Depth = 1 5/8 in.
 * Domestic Weight limit: 70 lbs

Step 1: compute the volume of the box
Formula: Length x Width x Height = Volume (the units multiply too)

Beware: Students seem to pay more attention to the USPS image with "8.5 in x 5.5 in x 1.5 in" which is not the same. It is clear that Paul Sherman used the exact values, and the students should too if they are to compare their results to his.

Step 2: Use the density of common objects to obtain the mass of a full box (neglecting the cardboard)
Formula: Volume x Density = Mass (metric optional).

Avoiding metric may lower the bar, but in real life a person might need to be able to convert units (densities found online are commonly listed in metric). Even if metric is avoided, the calculation should be done with units, and involve the cancellation of in^3

Extra details for metric
Basic conversions
 * 1 in = 2.54 cm
 * 1 lb = 453.59 g

The conversions can be done in more than one way, for example:
 * 1) The volume could be converted to cm3, then multiplied by the density to get the mass in grams, then converted to pounds and compared with 70.
 * 2) The densities could be converted from g/cm3 to lb/in3, then multiplied by the volume.

Sample conversion (needed in the second approach) $$ 1 \frac{g}{cm^3}=1 \frac{g}{cm^3}\cdot \frac{1 lb}{453.59 g}\cdot \frac{2.54^3 cm^3}{1^3 in^3} =\frac{2.54^3 }{453.59} \frac{lb}{in^3}\approx 0.036 \frac{lb}{in^3} $$

Step 2a (optional) Estimate the error
Have the students redo their calculations with both the density and the volume rounded up by 1 in the last place.

Step 3 Compare and draw conclusions
Note: Many students may say "No" to the first question below. The values are highly sensitive to rounding error. His values are accurate enough for his conclusions to be correct. Step 2a is intended to illustrate the fact that even rounding error will not cause the conclusions to be incorrect.

"Questions"
 * Are the numerical values posted by Paul Sherman correct? 
 * What might be a reasonable weight limit?
 * Would including the mass of the cardboard box itself change the answer significantly? Why?

Assignments
You're welcome to suggest exercises, activities, assignments, or projects based on the material of this lesson.

Resources
USPS Flat Rate Small Box https://store.usps.com/store/product/shipping-supplies/priority-mail-flat-rate-small-box-P_SMALL_FRB

Densities:
 * https://www.lenntech.com/periodic/elements/os.htm
 * https://www.thoughtco.com/table-of-densities-of-common-substances-603976
 * https://cedarstripkayak.wordpress.com/lumber-selection/162-2/
 * https://www.paperonweb.com/density.htm
 * https://hypertextbook.com/facts/2004/ShayeStorm.shtml

Background
Volume
 * https://www.youtube.com/watch?v=RxkRlIAucMk

Fractions
 * https://www.youtube.com/watch?v=alstJ37BoZo
 * https://www.youtube.com/watch?v=bf9GSi60Hr8
 * https://www.khanacademy.org/math/arithmetic/fraction-arithmetic

Decimals
 * https://www.youtube.com/watch?v=2xGzQXn3WUQ
 * https://www.khanacademy.org/math/arithmetic/arith-decimals

Explorations
''You're welcome to share references for additional learning and exploration, such as links to other articles, videos, spreadsheets, or computer code. When an open-access substitute is unavailable, links to paywalled sites are acceptable in this section.''

Feedback
Have you found this lesson plan helpful? Tell us about it!

Just click Endorse below to open up an editor and type your comments. When you're ready, they'll appear at the bottom of this section to help other educators looking for good lesson plans.

(Alternatively, if you see a way to improve this lesson plan, be bold and make an edit! You're also welcome to discuss the lesson plan or provide constructive feedback on its |Discussion page.)