Definition
A force, or the resulting deformation, that causes two adjacent parts of a material or fluid to slide past each other in opposite or differing directions along a parallel plane. In aviation, the term is applied both to mechanical loads on structures and fasteners, and to the relative motion between adjacent layers of air.
Plain English
Shear is what happens when two things side by side are pushed in different directions, so they try to slide past each other. Think of pushing the top of a deck of cards sideways while the bottom stays still — the cards slide across one another.
Context Anchor
Seen in aircraft structure discussions and in weather discussions, especially when pilots talk about wind shear near storms, fronts, or the runway.
Derivation
From Old English 'sceran', meaning to cut or divide. The same root gives us 'shears' (cutting tool) and 'sheared' sheep. The connection is the cutting-by-sliding action: shear forces try to slice one layer past another rather than pull or compress it.
Why Pilots Care
Can produce sudden airspeed changes that lead to stalls, overspeeds, or loss of control near the ground.
Analogy
Think of sliding the top card of a deck sideways while the card under it stays still. That sideways sliding action is the basic idea of shear.
Intuition Check
Shear does not just mean “cut off” here. In aviation, it usually means sideways sliding force between nearby parts, or a sharp change in wind between nearby areas of air.
Example Sentence 1
The rivets along the wing skin are loaded primarily in shear, so they are sized to resist the sliding force between the skin and the underlying structure.
Example Sentence 2
Strong shear at 200 feet forced the crew to execute a go-around.