3-PS2-4: Defining a Problem Magnets Can Solve
Also called NGSS 3-PS2-4 · Topic: Forces and Interactions · Physical Science
The Official Wording
Define a simple design problem that can be solved by applying scientific ideas about magnets.
Clarification statement: Examples of problems could include constructing a latch to keep a door shut and creating a device to keep two moving objects from touching each other.
NGSS Lead States, 2013 · Read it on nextgenscience.org · checked October 15, 2026
What 3-PS2-4 Means in Plain English
Third graders spot an everyday problem that a magnet could help fix, like a cupboard door that swings open. They describe what a good solution must do, the limits on materials or size, and how they would know it worked.
The focus is on defining the problem clearly using what students know about magnets, which pull iron and steel and attract or repel each other. It builds on 3-PS2-3 and on K-2-ETS1-1, and leads to the full design cycle in 3-5-ETS1-1.
3-PS2-4 I Can Statements
- I can describe a problem that a magnet could help solve.
- I can list what a good solution must do.
- I can use what I know about magnets to plan a design.
3-PS2-4 Worked Example
A design challenge built from a cereal box cupboard, a fridge magnet and a steel bottle cap.
How can we keep a cardboard cupboard door from swinging open on its own?
Set It Up: A cereal box with a door cut into one side, a flat fridge magnet, a steel bottle cap, tape, and a chart for criteria.
- Describe the problem: the door drifts open when the box is tipped or bumped.Problem statement written
- List criteria: the door stays shut when tipped, but one finger can still open it.2 criteria
- List constraints: use only the magnet, the cap and tape.Materials limit
- Sketch two plans: magnet on the door and cap on the frame, or the reverse.Plan A and Plan B
- Build Plan A, tip the box ten times and check the door.Door stayed shut 10 of 10
- Test whether the door opens with one finger.One finger is enough: criteria met
A fridge magnet on the door and a bottle cap on the frame kept the door shut in every tip, yet one finger could still pull it free.
Why it works: A magnet pulls on steel without hooks or glue, so a weak magnet can hold a light door closed and still let go when a finger tugs it.
Common Mistakes with 3-PS2-4
Building before defining the problem
Taping magnets everywhere before saying what the latch must do
Try this: Write the problem, criteria and limits first. A clear list tells you what to build and how to judge it.
Using two pieces that do not attract
A magnet taped across from a strip of aluminum foil
Try this: Check that the second piece is steel or another magnet with the opposite end facing. Magnets do not pull on aluminum.
Forgetting the door must still open
“It works! Nobody can open it now.”
Try this: Add a criterion that the door opens with one finger. A latch that never lets go fails half of its job.
Where 3-PS2-4 Fits
Practice 3-PS2-4
Quick Check
- What is a criterion in a design problem?
- Why would a steel bottle cap work in a magnet latch but a plastic cap would not?
- Name another problem a magnet could help solve.