Back More
Salem Press

Table of Contents

Principles of Physics

Speed

by Casey M. Schwarz, PhD

Fields of Study

Acoustics; Harmonics; Classical Mechanics

Summary

Speed is the distance traveled divided by the amount of time it takes to travel that distance. Waves are a disturbance that travels through a medium and transports energy. The speed of a wave is the distance traveled by a given point on the wave in a given amount of time.

Principal Terms

  • frequency: the number of oscillations, wavelengths, or cycles per unit of time.

  • sound barrier: the effects created when an object travels faster than the local speed of sound.

  • speed of sound: a sound wave’s traveled distance per unit of time.

  • velocity: the rate of change of position in a specified direction of motion.

  • wave propagation: the manner in which a wave travels.

  • wavelength: the distance between adjacent crests or troughs in the wave.

Speed and Velocity

The speed of an object is the rate at which it travels a certain distance. Velocity is speed with a direction of motion associated with it. Speed and velocity both have the dimensions of a length divided by a time. The International System of Units (SI) unit of speed is the meter per second.

Speed falls under a variety of physics disciplines including classical mechanics, astronomy, electromagnetism, and acoustics and can be related to many physics fundamentals, such as acceleration, force, and mechanical power. Newton’s laws of motion, harmonic motion, and vibration all involve speed.

Italian scientist Galileo Galilei (1564–1642) was one of the first to investigate speed. Galileo measured speed by observing the change in distance an object covered and the time it took to do so.

Speed is the distance traveled over the time it takes to travel; for a sound wave, it is a measure of the distance of one wave cycle divided by the time it takes for one wave cycle. Wave speed can be calculated by multiplying the wavelength by the frequency of a wave. If the frequency of a sound is kept constant at 100 Hz in air, water, and steel, the wave’s speed will increase as the wavelength is lengthened.

POP_Speed_illustration.tif

Wave Propagation

A wave can be described as a disturbance that travels from one place to another carrying energy. Wave propagation is the manner in which waves travel. Wave propagation through a medium is slower than through a vacuum because the atoms of the medium absorb some of the energy of the wave as it passes through.

There are three main types of waves: mechanical, electromagnetic, and matter waves. Matter waves, or De Broglie waves, are propagated in particles and electrons. Mechanical waves include water waves, seismic waves, and sound waves. They are governed by Newton’s laws and can only propagate through a material medium. Electromagnetic waves include light waves and radio waves. They can propagate through a vacuum or a medium.

Wave Speed

A wave can be described by its speed, wavelength, and frequency. For a mechanical wave, the wave speed is determined by the properties of the material through which it travels. Wave speed is the wavelength multiplied by wave frequency. For example, if a sound wave travels through different materials but its frequency remains constant, then the wave’s speed increases as the wavelength increases.

Speed of Sound

Mechanical waves are used every day in music, Doppler radar, and medical imaging, among other applications. Understanding wave properties, including speed, wavelength, and frequency, is necessary for predicting waves’ effects and uses. For example, the speed of sound, in dry air under normal atmospheric pressure and temperature, is 343 meters per second (1,127 feet per second). If an object such as an airplane travels faster than the speed of sound, it breaks the sound barrier. This event can be accompanied by a shock wave that produces a burst of sound, or sonic boom.

Citation Types

MLA 9th
Schwarz, Casey M. "Speed." Principles of Physics, edited by Donald R. Franceschetti, Salem Press, 2016. Salem Online, online.salempress.com/articleDetails.do?articleName=POP_0109.
APA 7th
Schwarz, C. M. (2016). Speed. In D. R. Franceschetti (Ed.), Principles of Physics. Salem Press. online.salempress.com.
CMOS 17th
Schwarz, Casey M. "Speed." Edited by Donald R. Franceschetti. Principles of Physics. Hackensack: Salem Press, 2016. Accessed September 20, 2026. online.salempress.com.