Definition
In a right triangle, the sine of an acute angle is the ratio of the length of the side opposite that angle to the length of the hypotenuse. It is a trigonometric function written as sin(angle), producing a value between 0 and 1 for angles between 0° and 90°.
Plain English
Sine is a number you get from an angle. In a right triangle, it tells you how big the side across from the angle is compared to the longest side. The bigger the angle (up to 90°), the bigger the sine.
Context Anchor
Seen in aviation maintenance math when working with angles, measurements, drawings, and force calculations.
Derivation
From the Latin sinus, meaning 'a curve' or 'fold.' Medieval translators picked the word when working from Arabic mathematical texts, and it stuck. The name itself doesn't describe what sine does — you just have to learn it as a fixed math term.
Why Pilots Care
Many aircraft maintenance tasks — resolving forces on a control surface, calculating component loads, or working out angular measurements — rely on sine. Getting it wrong gives the wrong number, which can mean an incorrect adjustment or rigging.
Grounding Statement
Picture a right triangle with one angle marked. Sine of that angle = (side across from it) ÷ (longest side, the hypotenuse).
Intuition Check
Sine does not mean sign, as in a symbol or indication. Here it is a math relationship between an angle and two sides of a right triangle.
Example Sentence 1
To find the vertical component of the cable tension, the technician multiplied the total tension by the sine of the rigging angle.
Example Sentence 2
Aircraft alternators produce voltage that varies according to the sine of the rotation angle.