Build, Test, Repeat: Three Engineering Challenges Every Young Inventor Should Try

Engineering is the art of solving real-world problems through design, testing, and iteration. Unlike many subjects taught in schools, engineering is inherently hands-on. You cannot learn to build by reading about building. You learn to build by building, by watching a structure collapse, by figuring out why it fell, and by building it better the next time.

The three challenges in this article are designed for children aged six and older and use materials that most families already have at home. Each challenge introduces a genuine engineering principle, the same principles used by professional engineers designing skyscrapers, bridges, and spacecraft. The goal is not perfection. The goal is the process: think, design, build, test, fail, redesign, and improve.

Challenge 1: The Egg Drop — Understanding Impact and Energy

The Egg Drop Challenge is one of the most widely used engineering activities in schools around the world. The task is simple: design a container that will protect a raw egg from breaking when dropped from a height. The engineering, however, is anything but simple.

The Brief

Design and build a protective device for a raw egg. The egg must survive a drop from at least 1.5 metres (roughly the height of a dining table when you stand on a chair). No hard shells (like plastic boxes) are allowed. You must use only soft or flexible materials.

Recommended Materials

• Drinking straws
• Cotton balls or cotton wool
• Bubble wrap
• Newspaper or tissue paper
• Rubber bands
• String
• A small plastic bag (for a parachute)
• Sticky tape

The Engineering Principles

When an egg falls, it accelerates due to gravity at 9.8 metres per second squared (on Earth). When it hits a hard surface, it experiences a sudden deceleration, and the kinetic energy of the fall must go somewhere. If that energy is concentrated in a small area over a short time, the shell cracks. Your job as the engineer is to spread the energy over a larger area and a longer time.

There are two primary strategies professional engineers use in crash protection, and you can use both in your egg protector:

1. Energy Absorption (Crumple Zones): Modern cars are designed with crumple zones, sections of the car body that deliberately deform during a crash. The deformation absorbs kinetic energy and converts it into heat and the physical work of bending metal. Cotton balls and bubble wrap serve the same function in your egg protector. They compress on impact, absorbing energy gradually instead of all at once.
2. Air Resistance (Parachutes): A parachute slows the fall by increasing the surface area exposed to air, thereby increasing the drag force. The slower the egg falls, the less kinetic energy it has at impact, and the less force the container needs to absorb. Real parachutes used in aerospace follow this exact principle.

Engineer’s Log: After each drop, examine the egg and the container. Where did the container compress? Did it rotate in the air? Did the parachute open fully? Write down three observations and one change you would make for the next attempt. This is the iterative design process used in professional engineering.

Challenge 2: The Spaghetti Bridge — Structural Engineering

Dry spaghetti is brittle. A single strand snaps with almost no effort. Yet, when arranged correctly, spaghetti can support a remarkable amount of weight. This challenge introduces the concept of structural geometry, the idea that the shape and arrangement of materials matters as much as the material itself.

The Brief

Build a bridge using only dry spaghetti and marshmallows (or tape) that can span a gap of 30 centimetres between two stacks of books. Test how much weight it can hold by carefully placing coins, small toys, or other small objects on the bridge deck until it collapses. Keep track of the weight.

Materials

• One packet of dry spaghetti
• Mini marshmallows or masking tape (for joints)
• Two equal stacks of books (to act as the bridge supports)
• Small coins or weights for testing

The Engineering Principles

Bridges must handle two primary forces: compression (pushing inward) and tension (pulling outward). When a load is placed on a flat beam bridge, the top of the beam is compressed while the bottom is stretched. This is why a flat piece of spaghetti placed across the gap breaks almost immediately when loaded. The spaghetti is strong under compression along its length but weak under bending forces.

The solution is geometry. A triangle is the strongest geometric shape in structural engineering because it cannot be deformed without changing the length of one of its sides. Squares, rectangles, and other four-sided shapes can be pushed into parallelograms, but triangles resist this. This is why you see triangular patterns, called trusses, in real bridges, roof structures, and even the Eiffel Tower.

When building your spaghetti bridge, try to incorporate triangular trusses on either side. Connect them across the top to form a box-truss structure. You will likely find that this design holds significantly more weight than a simple flat bridge, even though you are using the same brittle material.

The record for spaghetti bridge competitions, held at universities worldwide, exceeds 400 kilograms for bridges weighing less than one kilogram. That is the power of good structural design applied to even the weakest materials.

Challenge 3: Paper Helicopters — Aerodynamics in Action

This challenge uses nothing but a strip of paper and a paperclip to explore the principles of aerodynamics, the way air interacts with objects moving through it. Paper helicopters (also called rotocopters) are used in real scientific research as simple models for studying autorotation, the same phenomenon that allows real helicopter rotors to slow a descent even if the engine fails.

How to Build a Paper Helicopter

1. Cut a rectangular strip of paper approximately 20 centimetres long and 5 centimetres wide.
2. Starting from one end, cut a slit down the centre of the paper, stopping at the midpoint. This creates two flaps, which are your rotor blades.
3. Fold one blade toward you and the other blade away from you, creating a T-shape when viewed from above.
4. At the opposite end (the stem), make two small folds inward from each side to narrow the base, then fold the stem upward to create a weight holder.
5. Attach a paperclip to the bottom of the stem for weight.
6. Hold the helicopter high above your head and release it. It should spin rapidly as it falls.

The Engineering Principles

As the helicopter falls, air pushes against the angled blades. Because the two blades are folded in opposite directions, the air deflects off each blade in opposing directions, creating a torque (rotational force) that causes the helicopter to spin. The spinning blades then act like a real helicopter rotor in autorotation: they generate a small amount of lift and significantly increase drag, slowing the descent.

The paperclip at the bottom serves two purposes. First, it adds mass, which moves the centre of gravity below the rotor blades, stabilising the helicopter and preventing it from tumbling. Second, it provides enough weight that the helicopter actually falls rather than floating unpredictably.

Design Challenge: What happens if you make the blades shorter? Longer? Wider? Does adding a second paperclip change the speed? Create a data table and record the fall time for each design from the same height. You are now conducting a controlled experiment with independent and dependent variables, exactly how professional scientists and engineers work.

The Engineering Design Process

All three challenges above follow a structured process that engineers use in the real world. This process, known as the Engineering Design Process, is typically represented as a cycle:

1. Define the Problem: What exactly are you trying to achieve? What are the constraints (available materials, time, rules)?
2. Research and Brainstorm: Look at how others have solved similar problems. Generate multiple ideas before committing to one.
3. Plan and Design: Sketch your design on paper before building. Label the materials you will use.
4. Build a Prototype: Construct a working model. It does not need to be perfect.
5. Test: Put your prototype through the challenge. Record the results objectively.
6. Evaluate and Improve: What worked? What failed? What would you change? Make the change and test again.

This cycle does not end. Professional engineers may go through dozens or even hundreds of iterations before finalising a product. The Wright Brothers tested over 200 wing designs before their first successful flight. Failure is not something to avoid in engineering. It is the primary teacher.

So gather your materials, set up your workspace, and start building. Every collapsed bridge and cracked egg teaches you something that no textbook ever could. That is the power of engineering.