Which Magnetic Pole?
About
A bar magnet with clearly labelled poles hangs above a row of smaller magnets, each mounted on a pin so it can spin freely. Drag the known magnet around and the pivoting magnets swing to follow it, their south ends always turning toward its north end because opposite poles attract. Watching the alignment happen makes the rule concrete: the ends that seek each other out are opposites, and the ends that swing away are alike.
Each pivoting magnet is modelled as a pair of magnetic poles, and the force between any two poles falls off with the square of the distance, so each magnet settles at its own angle depending on where it sits relative to the known magnet. They do not snap into place either: each one swings round, overshoots slightly, and rocks back before coming to rest, exactly the way a real compass needle behaves. Students can change how many pivoting magnets are in the scene and flip the known magnet's poles to test a prediction. For an assessment, pressing Hide poles blanks the pivoting magnets to unlabelled grey, turning the demonstration into an identification task where the motion is the only available evidence.
Learning Goals
- Identify which end of a magnet is north from how it responds to a magnet with known poles, with the labels hidden
- State and apply the rule that opposite poles attract and like poles repel
- Predict which way a pivoting magnet will turn before releasing the known magnet, then test the prediction
- Describe how the angle a magnet settles at depends on where the known magnet is placed relative to it
- Explain why reversing the known magnet's poles reverses every pivoting magnet in the scene
- Recognise that a magnet at rest in a field has settled at the angle where the turning forces on its two ends balance
How to Use
- Drag the known magnet with a finger, stylus or mouse. Tapping anywhere on the stage moves it straight to that spot
- Prefer the keyboard? Tap the stage once to focus it, then use the arrow keys to slide the magnet in any direction
- Choose how many pivoting magnets to show, from one up to five, using the numbered buttons
- Watch which end follows the red end of the known magnet — that end is south
- Park the known magnet at one end of the row and note that every magnet points toward it at a different angle
- Press Flip known magnet and predict what will happen before it takes effect
- Press Hide poles to blank the pivoting magnets to unlabelled grey, so students identify the poles from the motion alone. Press again to check the answer