Definition
A natural physical force produced by moving electric charges (such as electrons) that causes certain materials -- chiefly iron, nickel, and cobalt -- to attract or repel one another and to align with a magnetic field. The Earth itself produces a large-scale magnetic field, and aircraft compasses use this field to indicate direction.
Plain English
The invisible force that makes magnets stick to iron and makes a compass needle point north. The Earth acts like a giant magnet, and pilots use that fact to find their heading.
Context Anchor
Seen in instrument flying when learning how a magnetic compass works and why compass headings may not match true geographic north exactly.
Derivation
From the Greek 'magnetis lithos' meaning 'stone of Magnesia' -- a region in ancient Greece where naturally magnetised rocks (lodestones) were first found. Knowing this anchors the idea that magnetism is a property of certain materials and the field they produce, not something abstract or man-made.
Why Pilots Care
Aircraft magnetic compasses depend on the Earth's magnetism for direction; pilots must understand its effects to correct for deviation and variation during instrument flight.
Grounding Statement
The same force that makes a fridge magnet stick is the force that aligns the compass needle in the cockpit.
Intuition Check
Magnetism is not only the pull of a small handheld magnet. In this context, it mainly means Earth’s magnetic field and how that field affects compass direction.
Example Sentence 1
The aircraft's compass relies on magnetism to align with the Earth's magnetic field and show the pilot a heading.
Example Sentence 2
Local magnetic disturbances near the aircraft can cause temporary errors in the compass until the pilot compensates.