An Overview of the Waves
When we stand on the beach, we observe that water is moving towards shore rolling in and out. These are the water waves. These waves are formed by the movement of wind across a standing body of water on the beach, which creates disturbances and the waves travel in circular paths. The disturbances propagate with wave speed and water molecules remain at the same position. Water waves are surface waves and they are made of a combination of longitudinal and transverse waves. These waves are formed by the interaction of the Earth, the Sun, and the Moon. Water waves have crests and troughs.
What is Wave?
The rise and fall of water caused by friction of the wind on the water surface is called a wave. A wave is a disturbance on the surface of the body which is travelling in a forward direction. This disturbance is in the form of a ridge or a swell. A wave is an up and down distortion on the water surface. Waves can be standing waves or progressive waves. In progressive waves, crest and trough travel at the same speed in the perpendicular direction. In standing waves, there is no progression. The up and down motion of a water wave is simple harmonic motion.
What are Water Waves?
Water waves are surface waves and they are made of a combination of longitudinal and transverse waves. These waves are formed by the interaction of the earth, the Sun, and the Moon. Water waves have crests and troughs. The source of most waves on the sea surface is wind.
Characteristics of water waves are listed below:
Crest and Trough - The peak of the wave is called as crest and the bottom point of wave is called as trough.
Wave Amplitude - Half of the wave height is called as amplitude.
Wave Height - The distance between the crest and trough is wave height.
Speed - Rate of the wave travelling in water.
Wave Frequency - The total number of waves passing through a point in one second is called as wave frequency.
Wavelength - The distance between two crests is known as wavelength.
Types of Waves Ocean
Wind Waves - These are the most common waves. In these waves, wind transfers a lot of energy when it comes in contact with the water surface. This forms ripples in water. The more substantial the wind, the larger the waves produced.
Tidal Waves - These waves arise due to gravitational force between the earth and the Moon. The ocean water remains in its place because of the earth’s gravity but the moon's gravity attracts water towards itself. This causes the wave to rise and fall. When the moon is closer to the side of the earth, it is called high tide and on other hand, it is called low tide. Powerful sea waves produced in the ocean are called tides.
Underwater Explosions - Bigger waves like tsunamis are caused due to underwater explosions or earthquakes in oceans.
There are three types of sea waves - Tsunamis, swell waves, and wind surges. The tide which attains maximum height is called the spring tide.
Difference Between Waves and Tides
Due to the force exerted by the wind on the water, waves are produced and tides are produced due to the gravitational effect between the Sun, Moon, and the earth.
Waves are generally produced in shallower parts and tides are produced in deeper parts.
Waves occur all the time due to wind and tides occur twice a day with a time gap of 12 hours and 35 minutes.
Work of Sea Waves
Erosion and deposition due to sea waves give rise to coastal landforms. Hollow caves on rocks are formed due to waves. These caves are called sea caves. When these caves become bigger due to waves, they are called Sea arches. Steep coast rising vertically above sea water is sea cliff. All these formations happen due to waves.
Interesting Facts
Waves transport only energy, not matter.
Water waves are very unusual as they can have different speeds.
There are two high tides and two low tides each day.
Solved Problems
1. The speed of a wave in a certain medium is 1000m/s. If 3600 waves pass from a certain point in 2 minutes, find the wavelength.
Solution: Given,
Speed of wave \[\upsilon = 1000m/s\]
Frequency of wave n= 3600waves/2min= 3600waves/120sec = 30 waves/sec
We know that wavelength= \[\lambda = \dfrac{\upsilon }{n}\] = 1000/30 = 33.33m
Therefore, wavelength=33.33m
2. Obtain the frequency of the wave if its wavelength is 50m and the speed of the wave is 2500m/s.
Solution: Given,
Wavelength \[\lambda \]= 50m
Speed of wave= 2500m/s
We know that frequency= \[n = \dfrac{\upsilon }{\lambda }\] = 2500/50 = 50 waves/sec.
Summary
The rise and fall of water caused by friction of the wind on the water surface is called a wave. A wave is a disturbance on the surface of the body which is travelling in a forward direction. Water waves are surface waves and they are made of a combination of longitudinal and transverse waves. These waves are formed by the interaction of the earth, the Sun, and the Moon.
FAQs on Water Waves
1. What are water waves and how are they typically generated?
A water wave is a disturbance on the surface of a body of water, such as an ocean or lake, that travels in a forward direction. These waves are primarily generated by the friction of wind blowing across the water's surface. This transfers energy from the wind to the water, creating ripples that can grow into larger waves. While wind is the most common cause, they can also be formed by gravitational forces (tides) or seismic events like underwater earthquakes (tsunamis).
2. What are the key characteristics used to describe a water wave in Physics?
The fundamental characteristics of a water wave, as per the CBSE/NCERT syllabus for 2025-26, are:
- Crest: The highest point of the wave.
- Trough: The lowest point of the wave.
- Wavelength (λ): The horizontal distance between two consecutive crests or troughs.
- Wave Height (H): The vertical distance between a crest and a trough.
- Amplitude (A): Half the wave height (H/2), representing the maximum displacement from the equilibrium water level.
- Wave Frequency (f): The number of waves that pass a fixed point in one second.
- Wave Speed (v): The rate at which the wave disturbance travels through the water.
3. What is the main difference between ocean waves and tides?
The primary difference between waves and tides lies in their cause. Waves are generally created by the energy transferred from wind blowing over the water's surface. In contrast, tides are the long-period rising and falling of sea levels caused by the gravitational forces exerted by the Moon and the Sun on the Earth. Waves are surface phenomena, while tides involve the movement of the entire body of water.
4. How can a water wave be both transverse and longitudinal at the same time?
A water wave is a unique combination of both wave types. As the wave propagates, the water particles move in a circular or orbital path. The up-and-down motion of this orbit is the transverse component (perpendicular to the wave's direction), while the back-and-forth motion is the longitudinal component (parallel to the wave's direction). This combined orbital motion is why water waves are considered surface waves with characteristics of both types.
5. Do water waves actually transport water across the ocean? Explain the energy transfer.
No, this is a common misconception. Water waves primarily transport energy, not matter (water), over long distances. The water particles themselves mostly oscillate in a small circular path around their equilibrium position and return to roughly the same spot after the wave passes. Think of a wave in a stadium: the people stand up and sit down (oscillate), but they don't run around the stadium. Similarly, it's the disturbance or energy that moves forward through the water.
6. Why do ocean waves “break” as they approach the shore?
Waves break near the shore due to their interaction with the seabed. As a wave moves into shallower water, its lower part starts to drag against the ocean floor, causing it to slow down. However, the top of the wave (the crest) continues to move at a faster speed. This speed difference causes the wave to become unstable and steepen until the crest outruns the base and topples over, creating the familiar 'breaking' wave or surf.
7. How is the speed of a water wave determined in deep versus shallow water?
The speed of a water wave depends on the depth of the water relative to its wavelength. There are two main examples:
- Deep Water Waves: In water that is deeper than half the wave's wavelength, the wave speed is determined by its wavelength. Longer wavelength waves travel faster than shorter ones.
- Shallow Water Waves: In water that is much shallower than the wavelength (e.g., near the coast), the wave speed is determined primarily by the water's depth. The wave travels faster in deeper water and slower in shallower water.
8. What are some real-world examples of different types of water waves?
Water waves manifest in various forms with different causes and characteristics. Key examples include:
- Wind Waves: The most common type, seen on any lake or ocean, caused by wind blowing across the surface.
- Tidal Waves (Tides): The regular rise and fall of the sea level caused by the gravitational pull of the Moon and Sun.
- Tsunamis: Extremely large and powerful waves caused by major underwater disturbances like earthquakes, volcanic eruptions, or landslides, not by tides.
- Ripples: Very small waves, often the initial stage of wind wave formation, where surface tension is the main restoring force.
