Grade by Grade
D. Structures and Mechanisms · Strong and Stable Structures

Form and Function: Shaped for the Job

D2.2 D2.1 A1.5About 35 minutes
Learning goals
  • I can explain what form and function mean.
  • I can explain how the form (shape) of a structure helps it do its function (job).
  • I can sort structures into solid, frame and shell structures.
  • I can compare structures that have the same function but different forms.

Words to know

form
The shape and size of a structure, and how it is put together.
function
The job a structure does.
solid structure
A structure that is filled in, with no hollow space inside, like a brick wall or a stone pile.
frame structure
A structure made of parts (like poles, sticks or beams) joined together, like a tent frame, a ladder or a house frame.
shell structure
A structure with a hollow inside and a thin, curved outside, like an egg, a bowl, a dome or an igloo.

Why are chairs different?

Think of a kitchen chair, a high chair for a baby, a camping chair and a wheelchair. They all have the same main function: to hold up a person who is sitting. But they look very different!

  • The high chair is tall with a tray and a safety strap, so a baby can sit at the table safely.
  • The camping chair folds up small, so you can carry it.
  • The wheelchair has big wheels, so a person can move around while sitting.

Each chair has a form (a shape) that fits its job.

A wooden kitchen chair, a wooden high chair with a tray and strap, and a blue folding camping chair stand side by side on a porch.
All three chairs have the same function, holding up a person, but each has a different form. Can you spot the tray, the strap and the folding legs? AI-generated image

Form and function

  • Form means the shape and size of a structure and how it is put together.
  • Function means the job it does.

Engineers say: form follows function. That means you first decide what job the structure must do, then you choose a shape that helps it do that job well.

Worked example

Let's figure out why a shape fits a job

A ladder has two long sides and many short steps (rungs). Why is it shaped like that?

  1. Function: a ladder helps a person climb up high.
  2. The two long sides are tall so the ladder reaches up high.
  3. The rungs are spaced about one step apart, so your feet can move up one at a time.
  4. The rungs join the two sides together, which keeps the ladder from bending apart.

The ladder's form (tall sides with evenly spaced rungs) helps its function (climbing up safely).

Three kinds of structures

Scientists sort structures into three kinds by their form.

solidframeshell
Three kinds of structures: a solid brick wall, a frame made of poles joined together, and a hollow shell shaped like a dome.
KindWhat it is likeExamples
SolidFilled in. No empty space inside. Often heavy.a brick wall, a stone pile, a snowman, a dam made of earth
FrameParts like poles, sticks or beams joined together. Lots of empty space between the parts.a tent frame, a ladder, a house frame, a bicycle, an electric tower, a spider's web
ShellHollow inside with a thin, often curved outside that holds the shape.an egg, a bowl, a helmet, a dome, an igloo, a turtle's shell, a snail's shell
Solid, frame and shell structures

Some structures are a mix

Lots of structures use more than one kind. A house has a frame of wood inside the walls, sitting on a solid concrete base. A car has a metal frame covered by a shell of thin metal.

Worked example

Let's sort and explain

Is a bicycle helmet a solid, frame or shell structure? Why is its form good for its function?

  1. A helmet is hollow inside, with a thin, curved outside. That is a shell structure.
  2. Function: to protect your head if you fall.
  3. The curved shell fits around your head. The curve spreads out the force of a bump over a big area, instead of one small spot.
  4. Because it is hollow, there is room for your head and soft padding inside, and it stays light enough to wear.

A helmet is a shell structure. Its curved, hollow form protects your head and is light to wear.

Worked example

Same job, different forms

A canoe and a rowboat both carry people on water. Compare their forms.

  1. Both have a shell form: hollow inside, with a thin, curved outside that keeps water out.
  2. A canoe is long and narrow with pointed ends. It slides through the water easily and is light to carry between lakes.
  3. A rowboat is wider and flatter. It is steadier but heavier.
  4. Each form fits how the boat is used.

Same function (carrying people on water), different forms: the canoe is narrow and light; the rowboat is wide and steady.

Seen from aboveCANOElong and narrow, pointed endsslides easily, light to carryROWBOATwider and flattersteadier, but heavierSame function (carry people on water), different forms
A canoe and a rowboat have the same function but different forms. Each shape fits how the boat is used.
Just for fun

Why is a ladder such a good friend?

It is always there to help you step up!

Hands-on activity

Form and function detective

You need: paper, a pencil, and things around your home.

  1. Find three cups or containers with the same function (holding a drink): for example a mug, a travel mug with a lid, and a baby's sippy cup.
  2. For each one, draw it and write one part of its form and how that part helps. Example: "The mug has a handle, so I can hold a hot drink without burning my fingers."
  3. Now go on a hunt. Find one solid, one frame and one shell structure at home. Hints: a stack of books, a chair, a bowl, an egg carton, a laundry basket, a tent, a drying rack.
  4. Explain your findings to a grown-up using the words form and function.

What to look for: a lid stops spills, a narrow spout helps a baby drink, a handle keeps fingers away from heat; a chair or drying rack is a frame, a bowl is a shell, a stack of books is solid.

Your turn

1

What does form mean?

2

What does function mean?

3

Is an egg a solid, frame or shell structure?

4

Is a ladder a solid, frame or shell structure?

5

Is a brick wall a solid, frame or shell structure?

6

Why does a camping chair fold up?

7

Name one structure that is a mix of two kinds.

More practice: warm-up

1

Is a bowl a solid, frame or shell structure?

2

Is a tent pole frame a solid, frame or shell structure?

3

Is a snowman a solid, frame or shell structure?

4

What is the function of a mailbox?

5

True or false: structures with the same function always look the same.

More practice: on your own

1

Why does a high chair have a tray and a strap?

2

Why is a slide smooth and sloped?

3

A spider's web is a natural structure. Is it a solid, frame or shell? Explain.

4

Why is a turtle's shell curved instead of flat?

5

Why does a snow shovel have a long handle and a wide, flat scoop?

Challenge

1

Design a chair for a kindergarten classroom. Describe two parts of its form and explain how each helps its function.

2

Why are bridges over wide rivers usually different from a plank across a small creek?

3

An egg carton is a shell structure. Explain how its form helps its function.

Check your understanding

Quiz

1.

Form means a structure's...

2.

Which is a shell structure?

3.

Which is a frame structure?

4.

Which is a solid structure?

5.

"Form follows function" means...

6.

A wheelchair, a camping chair and a high chair all have the same...

For parents and teachers

Big idea: The form (shape, size, how it is put together) of a structure is chosen to suit its function (job) (D2.2). Grade 3 students also sort structures into solid, frame and shell structures, which builds on Grade 1's idea of a frame. Explaining with the words form and function is scientific communication (A1.5).

How to help: Pick everyday objects with the same job and ask, "Why do these look different?" (a mug and a travel mug; a winter boot and a rain boot; a kitchen chair and a stool). Ask about one part at a time: "Why does it have a handle? A lid? A wide base?"

Common difficulties:

  • Mixing up form and function. Form is what it looks like; function is what it does.
  • Thinking a structure must be only one kind. Many structures mix kinds; a house is a frame on a solid base.
  • Calling anything round a shell. A shell is hollow with a thin outside. A solid ball of clay is round but solid.