Ages 8–12 · about 6 minutes

Putting the Whole Puzzle Together

If separate parts pass their tests, do we know the whole machine works?

Do this first · Try this at home

Check the links and the chain

Start with your hands. The reading makes far more sense afterwards.

You need: Paper, tape, scissors for an adult to use, a clear table and an adult helper

Tick each step as you do it

Ask your adult helper to cut six paper strips, including one narrower strip. Make a loop with one strip and tape it closed. Look at the join.
Link and tape the remaining strips into a short chain on the table. Do not put loops around your body or wear the chain. Predict what might happen when your helper lifts it.
Ask your adult helper to lift the chain briefly just above the clear tabletop, away from faces, then put it down. Do not tug. Record whether a join opened, a strip bent, or the chain stayed together.

0 of 3 steps done

What should I notice?

Notice: A prediction is not a result. The narrow strip might hold while a taped join opens, or the whole chain might stay together. Record what you actually observe. This paper model does not test a spacecraft.

Now read on to find out why it happens.

The big idea

Parts need tests. Their connections need tests too.

system: A set of parts that work together.
connection: A place or way that parts join or affect each other.
test: A planned check of what something does under stated conditions.

Working parts do not automatically make a working machine. The connections need tests too.

A child on a hilltop at sunset lifts the last piece of a giant jigsaw puzzle showing a starry sky, a calm sea, a glowing box and a floating silver disc, with a dog and a kite nearby. — An imagined puzzle about ideas in this book. Bringing pictures together does not show that a proposed machine has been built or tested.

Parts and connections

Engineers check individual parts and then how they interact. A part may need a different connection, power supply or temperature when it joins a system. These checks are part of integration.

Ask three concrete questions: which parts were connected, what should they do together, and what happened?

Record what happens

A narrow strip does not have to fail first. The tape, the paper and the way the chain is lifted all matter. A chain that stays together is also an observation.

Engineers test connected systems from their inputs through to their outputs. A result from one apparatus does not show that a different combination of devices will work.

A picture answers a different question

Our gravity arrows show the direction gravity acts, not the routes objects must travel. Around Earth, local down changes with your position. Turning the picture changes your view, not Earth's pull.

That diagram helps answer a question about gravity. It does not test a new engine.

Your turn

Six separate paper loops stayed closed. Have you tested the linked chain yet? What would you record when you do?

Choose one illustration from this book. What does it help you imagine, and what still needs a measurement?