# Choice of Unit

Examples, videos, and solutions to help Grade 8 students learn how the choice of unit determines how easy or difficult it is to understand an expression of measurement.

### Lesson 12 Student Outcomes

• Students understand how choice of unit determines how easy or difficult it is to understand an expression of measurement.
• Students determine appropriate units for various measurements and rewrite measurements based on new units.

Lesson 12 Summary • Students have reinforced their ability to read, write, and operate with numbers in scientific notation.

Classwork

Exercise 1
A certain brand of MP3 player will display how long it will take to play through its entire music library. If the maximum number of songs the MP3 player can hold is 1,000 (and the average song length is 4 minutes), would you want the time displayed in terms of seconds-, days-, or years-worth of music? Explain.

Exercise 2
You have been asked to make frosted cupcakes to sell at a school fundraiser. Each frosted cupcake contains about 20 grams of sugar. Bake sale coordinators expect 500 people will attend the event. Assume everyone who attends will buy a cupcake; does it make sense to buy sugar in grams, pounds, or tons? Explain.

Exercise 3
The seafloor spreads at a rate of approximately 10 cm per year. If you were to collect data on the spread of the seafloor each week, which unit should you use to record your data? Explain.

Exercise 4
Show that the mass of a proton is 0.938 GeV/c2

Exercise 5
The distance of the nearest star (Proxima Centauri) to the sun is approximately 4.013336473 x 1013. Show that Proxima Centauri is 4.2421 light-years from the sun.

Exploratory Challenge 2
Suppose you are researching atomic diameters and find that credible sources provided the diameters of five different atoms as shown in the table below. All measurements are in cm.

Exercise 6
What new unit might you introduce in order to discuss the differences in diameter measurements?

Exercise 7
Name your unit and explain why you chose it.

Exercise 8
Using the unit you have defined, rewrite the five diameter measurements.

Try the free Mathway calculator and problem solver below to practice various math topics. Try the given examples, or type in your own problem and check your answer with the step-by-step explanations.