Surface Waves in Water

View Assign Share Link Report

Surface Waves in Water

This lesson aligns with NGSS PS4.A

Introduction

Surface waves are disturbances that travel along the interface between two different mediums, most commonly between water and air. Surface waves in water are a familiar phenomenon, visible in oceans, lakes, rivers, and even smaller bodies of water. These waves, which move along the surface of a liquid, are typically generated by wind, earthquakes, or other disturbances. This article explores the basic characteristics of surface waves, the patterns they create, and the forces that shape their movement.

What Are Surface Waves?

In the case of water waves, the water surface oscillates up and down as energy is transmitted across the surface. The movement is not just vertical but involves a combination of vertical and horizontal motion, creating circular or elliptical paths for the particles of water beneath the wave.

These waves differ from internal waves, which propagate beneath the water's surface and affect deeper water layers. Surface waves are the ones most commonly observed because they are responsible for the familiar rolling and rippling of the water that we see.

Characteristics of Surface Waves

Wavelength: The wavelength is the horizontal distance between two consecutive crests (the highest point of a wave) or troughs (the lowest point). It determines the size of the wave.
Amplitude: Amplitude refers to the vertical height of the wave from its equilibrium position (usually the flat surface of the water) to the crest. Higher waves have greater amplitude.
Frequency and Period: Frequency and period are inversely related—if a wave has a high frequency, it will have a short period, and vice versa.
Wave Speed: For surface waves, the speed often depends on the depth of the water and the size of the wave.
Circular Particle Motion: One unique characteristic of surface waves in water is the circular motion of the water particles. As the wave passes, water molecules move in circular orbits. These orbits become smaller with depth, meaning that water molecules below the surface are less affected by the wave than those at the top.

Formation of Surface Waves

The most common cause of surface waves is the wind. When the wind blows across a body of water, friction between the air and the water surface transfers energy from the wind to the water. This energy creates ripples, which grow into larger waves if the wind continues. The strength and duration of the wind, as well as the size of the body of water, influence the size of the waves.

Wind waves typically start as small ripples that form capillary waves, which have very short wavelengths. As the wind continues, it generates gravity waves, which have longer wavelengths and are the type of waves we typically see in the ocean.

In addition to wind, waves can be generated by underwater disturbances like earthquakes or landslides, which create tsunamis. These waves can travel across entire ocean basins at high speeds and cause significant damage when they reach land.

Factors Influencing Wave Behavior

Several factors influence the formation, size, and movement of surface waves:

Wind Speed and Duration: The speed and consistency of the wind are crucial in determining the size of waves. Stronger winds create larger waves, and the longer the wind blows, the larger the waves become. The duration of the wind, therefore, plays a significant role in wave development.
Fetch: Fetch refers to the distance over which the wind blows across open water. A longer fetch allows more time and space for waves to develop and grow, resulting in larger waves. Shorter fetches, on the other hand, result in smaller, less developed waves.
Water Depth: The depth of the water affects wave speed and height. In deeper water, waves move faster, and their orbits are more circular. As waves approach shallower water near the shore, their speed decreases, and their orbits become more elliptical, causing the wave height to increase. This process, known as shoaling, leads to waves "breaking" as they reach the shore.
Gravity: Gravity plays a central role in wave formation. It is the restoring force that tries to flatten the water surface after a wave forms. This interplay between wind energy and gravity leads to the oscillatory motion of surface waves. When the wind stops blowing, gravity causes the waves to eventually settle and dissipate.

Conclusion

Surface waves are disturbances that travel along the interface between two different mediums, most commonly between water and air.
One unique characteristic of surface waves in water is the circular motion of the water particles. As the wave passes, water molecules move in circular orbits.
The speed and consistency of the wind are crucial in determining the size of waves.
Stronger winds create larger waves, and the longer the wind blows, the larger the waves become.

Related Worksheets: