# Modeling Prompt

How Big is That?

### In Class Launch

Use after Unit 3, Lesson 2

In this task, students will compare relative sizes or amounts using everyday 3D objects, like an eraser or a water glass. They will need to say how many of an object it would take to represent each size or amount that they want to compare, or how large or small the object would have to be so that just one of it would represent each size or amount, which will require scaling volumes and lengths accurately.

To give students an idea of what they will be asked to do, display an example for all to see. Examples can be found online—try search terms like “how many peas would fit in the sun” or “if the Earth were a grape.” Ask students what other sizes or amounts they might want to compare if they were writing a children’s book to explain a concept. For example, we might want to explain that animals can be very different sizes by comparing insects and blue whales. Or we might want to compare amounts of rainfall in the driest and wettest parts of the world.

Then ask students what objects they could use to represent the sizes or amounts that they suggest. For example, we could choose a marble to represent the size of the smallest insect and then calculate how many marbles, or how large a marble, would represent a blue whale. We could compare amounts of rainfall by representing the annual rainfall in the driest desert by one 8 ounce glass of water and then calculating how many glasses, or how large a glass, would represent annual rainfall in the wettest part of the Earth.

Tell students that in this task they will write part of a children’s book that compares different sizes or amounts. They will need to communicate clearly to their audience, so they should choose familiar objects and use illustrations to help the reader understand.