Designing Magnetic Solutions

One day, you notice something amazing: a giant magnet hangs above the conveyor belt. As the mixed materials roll underneath, the steel cans fly up and stick to the magnet, but the aluminum cans, glass bottles, and plastic containers keep rolling along. The magnet pulls only some objects and ignores the rest!

The recycling center needs a better magnet system because the old one misses some cans and sometimes the cans get stuck and won't drop off. They ask your class to help design a new magnetic solution. But there are rules you have to follow — like how much money you can spend, how big the magnet can be, and how fast the belt moves.

• Why does the magnet pull some cans up but not others?
• If you had to design a better magnet system, what rules or limits would you need to think about?
• How would you know if your magnetic solution actually works well?

Before we can design a magnetic solution, we need to understand two big ideas: how magnets work, and how engineers plan their designs. Engineers are people who use science to solve problems. They don't just start building — they think carefully about the rules they need to follow. These rules are called criteria and constraints.

Your investigation: Imagine your class is given the challenge of designing a magnetic tool that can pick up steel paper clips from a bin of mixed objects (paper clips, wooden beads, plastic buttons, and aluminum foil balls). Here is what you know:

• Goal: Pick up as many paper clips as possible in 30 seconds.
• Materials you can use: One bar magnet, one horseshoe magnet, one piece of string (30 cm), one craft stick, tape.
• Limit: The tool must be held in one hand.
• Limit: The tool cannot touch the bottom of the bin with your fingers.

What you would observe: Different magnet shapes attract paper clips from different distances. The horseshoe magnet might hold more clips at once. Taping a magnet to a stick lets you reach the bottom of the bin without using your fingers. The key is to identify which criteria (goals) and constraints (limits) matter most before choosing a design!

When we investigate designing a magnetic tool, we quickly discover that we can't just grab any magnet and start working. We first need to clearly state what the tool must do and what limits we have. Let's look at how criteria and constraints work together for a magnetic solution by examining real test data from three different designs.

Design C picked up the most paper clips — that's great for meeting the criterion of getting as many clips as possible. But it doesn't follow the constraint that the tool must be used with one hand. Even though it performed the best, it can't be the winning design because it breaks a rule. Design B picked up 17 clips while meeting all constraints. Based on the evidence, Design B is the best solution — it scores highest on the criteria while staying within all constraints.

This is exactly how real engineers think. They don't just pick the solution that works the "most." They pick the solution that best balances meeting the criteria while staying within the constraints. Sometimes that means the solution isn't perfect, but it's the best one that follows all the rules.

The big pattern we see in this lesson is called Influence of Engineering, Technology, and Science on Society and the Natural World. But we can also see a powerful crosscutting concept at work: Cause and Effect. When we change our design (cause), it changes how well the solution works (effect). And when we change the criteria or constraints (cause), different designs become the "best" one (effect).

This pattern — that changing the rules changes which solution is best — shows up everywhere, not just with magnets. Scientists look for cause and effect patterns in all areas of science. Let's see some examples:

Do you see the pattern? Every single problem — whether it involves magnets, birds, floods, or lunch — has criteria (what the solution must do) and constraints (what limits you must follow). When the criteria or constraints change, the best solution changes too. That's cause and effect in action!

Defining criteria and constraints isn't just something scientists do in a lab. People use this kind of thinking every day to solve real problems! Here are some real-world examples where magnets are used as solutions — and where criteria and constraints guided the design.

Before you start designing, define your criteria and constraints!

• 🎯 Criteria: The drawing must stay up for at least one day. No part of the drawing is covered.
• 🚧 Constraints: You can only use 2 small magnets. The magnets must not scratch the fridge. The holder must be easy for a kid to use.

Now think: What design would meet these criteria while staying within the constraints? Could you attach the magnets to a frame? Could you use them at the very top edge of the paper? Defining the criteria and constraints first helps you focus your ideas!

• Criteria — The goals or requirements that a solution must meet to be successful. Criteria answer the question: "What does the solution need to do?"
• Constraints — The limits or restrictions on a solution. Constraints answer the question: "What rules do we have to follow?" This includes limits on time, money, materials, and size.
• Magnetic force — The invisible push or pull that a magnet creates. Magnetic force can attract (pull toward) objects made of iron or steel without touching them.
• Non-contact force — A force that can act on an object without physically touching it. Magnetism and gravity are both non-contact forces.
• Engineering Design Process — The steps engineers follow to solve problems: define the problem, brainstorm solutions, compare and test, and improve.
• Solution — A design or plan that solves a problem. In engineering, a good solution meets its criteria while staying within its constraints.
• Attract — To pull toward. Magnets attract objects made of iron and steel.