Wednesday, November 18, 2009

Grade 4, Week 12, Day 3 ~ Ounces Are Oh So Confusing

Tons make sense; there are 2000 pounds in a ton. The boys are even perceptive enough to understand that the idiom That weighs a ton! means that something is heavy, not that it necessarily weighs 2000 pounds.

But ounces? Color the boys slightly confused. The train of thought goes like this: There are 16 ounces in a pound. A cup has 8 ounces. That means a cup weighs half a pound. Except it might not ~ fluid ounces and ounces as a measurement of weight are not the same thing.

8 fluid ounces of water will weigh 8 ounces, as will other liquids of the same density. 8 fluid ounces of honey weighs 12 ounces. Honey is sold by weight most of the time; I learned a long time ago that 24 ounces of honey by weight will fit into a container that holds 16 fluid ounces.

The word ounce comes from uncia, meaning 1/12, as an ounce was 1/12 of a Roman pound. But an ounce is only 1/16 of avoirdupois pound, which is the pound we use in the United States customary system.

I can't think of any way to teach this other than rote memorization. I didn't come up with a clever story and didn't find one in the various Waldorf materials I have.

Continuing Practice: Subtraction with Regrouping
Free Reading
Concepts Awakened: Adjectives
Main Lesson: Measurement
Afternoon Lesson: Gardening
Other Subjects: Social Studies (A History of US)

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