The time rate of change of displacement. This is often expressed as V, x, or dx/vt; **velocity** leads displacement by 90 degrees in time. Typical units for **velocity** are inches/second or millimeters/second, zero-to-peak. **Velocity** measurements are usually obtained with a mechanically activated velocity transducer and are used to evaluate machine housing and other structural response characteristics. Electronic integration of a **velocity** displacement signal. (Bentley Nevada Corporation, Field of Rotating Machinery Measurement, Monitoring and Analysis)

**Velocity of Sound in Gas**

The speed of sonorous vibrations through gases varies inversely as the square root of the weights of equal volumes of the gases, or, in other words, in the inverse ratio of the square roots of their densities. [Appleton's School Physics, page 377]

"To move suddenly a square inch of air at the **velocity** of his vibratory circuit, on full line of graduation and at a vibration only of 2,750,000 per second, would require a force at least of twenty-five times that of gunpowder, and at 21,000 lbs. per sq. inch it would be 525,000 lbs. per square inch. The finer the substance the greater the power and **velocity** under such vibrations." [JOHN ERNST WORRELL KEELY]

See Also

**Propagation**
**Snells Law**
**Table 9.1 - Velocity of Sound in various Materials**
**Velocity of Sound**
**Velocity Transducer**
**9.12 - Velocity of Sound and its Propagation Rate are Proportional**
**9.2 - Wave Velocity Propagation Questions**