Definition:Speed

Definition

The speed of a body is a measure of the magnitude of its velocity, taking no account of its direction.

It is, therefore, a scalar quantity.

Symbol

The usual symbol used to denote the speed of a body is $v$.

Examples

Speed of Sound in Air

The speed of sound in air at ground level on Earth is approximately $330 \, \mathrm {m s}^{-1}$.

Speed of Light

The speed of light, and that of other electromagnetic waves (in a vacuum) is a physical constant.

Information cannot travel faster.

Also known as

Some authors erroneously or carelessly refer to the speed of a body as its velocity.

But this is technically wrong if the author does not specify its direction as well as its magnitude.

Also see

• Results about speed can be found here.

Sources

• 1966: Isaac Asimov: Understanding Physics ... (previous) ... (next): $\text {I}$: Motion, Sound and Heat: Chapter $3$: The Laws of Motion: Forces and Vectors
• 1968: Murray R. Spiegel: Mathematical Handbook of Formulas and Tables ... (previous) ... (next): $\S 22$: Vectors and Scalars
• 1998: David Nelson: The Penguin Dictionary of Mathematics (2nd ed.) ... (previous) ... (next): speed
• 1998: David Nelson: The Penguin Dictionary of Mathematics (2nd ed.) ... (previous) ... (next): velocity
• 2008: David Nelson: The Penguin Dictionary of Mathematics (4th ed.) ... (previous) ... (next): speed
• 2008: David Nelson: The Penguin Dictionary of Mathematics (4th ed.) ... (previous) ... (next): velocity
• 2009: Murray R. Spiegel, Seymour Lipschutz and John Liu: Mathematical Handbook of Formulas and Tables (3rd ed.) ... (previous) ... (next): $\S 20$: Formulas from Vector Analysis: Vectors and Scalars
• 2014: Christopher Clapham and James Nicholson: The Concise Oxford Dictionary of Mathematics (5th ed.) ... (previous) ... (next): speed