Psychology & Psychiatry

Babies found to have greater imagination than previously known

In a new study published in Philosophical Transactions of the Royal Society B, scientists from Vienna-based Central European University have found that babies as young as 14 months old can consider several alternatives on ...

Psychology & Psychiatry

Larger pupils? You might just have gained someone's trust

Synchrony in heart rate, skin conductance and pupil diameter plays a big role in human social interactions, such as gaining trust or being attracted toward each other. This is what Eliska Prochazkova found in several lab ...

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Diameter

In geometry, a diameter of a circle is any straight line segment that passes through the center of the circle and whose endpoints are on the circle. The diameters are the longest chords of the circle. The word "diameter" derives from Greek διάμετρος (diametros), "diagonal of a circle", from δια- (dia-), "across, through" + μέτρον (metron), "a measure").

In more modern usage, the length of a diameter is also called the diameter. In this sense one speaks of the diameter rather than a diameter, because all diameters of a circle have the same length, this being twice the radius.

For a convex shape in the plane, the diameter is defined to be the largest distance that can be formed between two opposite parallel lines tangent to its boundary, and the width is defined to be the smallest such distance. For a curve of constant width such as the Reuleaux triangle, the width and diameter are the same because all such pairs of parallel tangent lines have the same distance. See also Tangent lines to circles.

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