# 11 – Three-Dimensional Solids

• Do you know what two Greek words the word geometry comes from? Geos, meaning earth, and metron, meaning measure.
• So, we should be able to use geometry to measure the earth.
• But the only shapes you’ve learned how to measure so far are flat and two-dimensional.
• Since the earth and most everyday objects aren’t flat, it’s time to go 3-D and learn about three-dimensional objects.
• In this unit you’ll use your knowledge of two dimensions to explore how those rules apply to three-dimensional shapes.
• You already know how to find the area of two-dimensional shapes.
• Now you’ll discover how to expand that understanding to find the surface area and volume of three-dimensional objects or solids.
• Imagine you just built this wooden planter.
• To finish the project you want to know how much stain you need for the outside, and how much potting soil the planter will hold.
• Knowing how to calculate surface area and volume is like adding a problem-solving power pack to your geometry toolbox that allows you to conquer a wide variety of real-world problems — and no 3-D glasses are required!
• In this unit, you’ll also learn about a special group of solids, called Platonic solids, which the ancient Greek philosopher Plato thought were the building blocks of the universe.