Words to know
structure
Anything, natural or built, that has a definite size and shape, holds its shape and supports a load.
load
The force or forces a structure has to hold up or resist, including its own weight.
solid structure
A structure made mostly of solid material all the way through. Its mass holds up the load.
frame structure
A structure built from a skeleton of parts (like beams, columns and braces) joined together. The skeleton holds up the load.
shell structure
A structure with a thin, often curved, outer layer that holds its own shape and surrounds an empty space. The shell holds up the load.
classify
To sort things into groups using clear rules.
Hook: three ways to hold up a load
Look around your home. A brick wall, a chair and an egg all hold up loads, but they do it in completely different ways.
- The brick wall is solid almost all the way through.
- The chair is a skeleton of legs, a seat frame and braces, with lots of empty space.
- The egg is a thin curved skin around an empty space (well, full of egg, but the shell does the holding).
Engineers sort structures into three big groups based on how they hold up loads: solid, frame and shell structures.
Remember from Grade 3
In Grade 3 you learned that a structure supports a load and holds its shape. You met solid, frame and shell structures, and you matched a structure's form (shape) to its function (job).
In Grade 7 you will classify structures more carefully, explain why each type works, and compare their strengths and weaknesses like an engineer.
The three types
1. Solid structures are made mostly of solid material. Their mass holds up the load and keeps them in place. Examples: a concrete dam, a brick wall, a stone pyramid, a snowbank, a solid wooden cutting board.
2. Frame structures are a skeleton of parts joined together. The parts carry the load, and there is lots of empty space between them. Some frames are covered (a house has walls over its wooden frame), but the frame does the holding. Examples: a hydro tower, a ladder, a bicycle frame, a chair, your own skeleton, a spider's web.
3. Shell structures have a thin outer layer that holds its shape and surrounds a space. A curved shell spreads the load across the whole surface. Examples: an egg, a pop can, a hockey helmet, a dome, a cardboard box, a turtle's shell.
Hands-on activityStructure classification hunt
You need: paper, a pencil and a ruler.
- Make a table with three columns: Solid, Frame, Shell.
- Walk through your home (and look out the window or go for a walk with a grown-up). Find at least 4 structures for each column. Look for big ones (a garage, a bridge, a hydro tower) and small ones (a mug, a bike, a lamp).
- For each one, write what part holds the load.
- Circle any structure that was hard to classify. Write why. (Hint: some structures use more than one type. You will learn about these next lesson.)
- Share your table with a grown-up. Explain two of your choices using the words solid, frame, shell and load.
What to look for: Solid: a brick wall, a concrete step, a stone. Frame: a chair, a bed frame, a bike, a fence, a swing set. Shell: a bowl, a bottle, a helmet, a box, a bathtub. Each choice should be explained by what holds the load.