​Introduction

When the wind blows, the surfaces of oceans, seas, lakes, and rivers move in patterns. When the wind blows harder, these patterns become bigger and more distinct. Each of these patterns of motion is called a wave, which is a disturbance that moves through a material from one location to another. The material through which waves are transmitted is called a medium. More disturbances in the medium generate more waves, and stronger disturbances create bigger waves.

They are trying to make their toy boats reach the other end of the tub without their hands having to touch the boats.

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Boy 1 appears to be moving his hand back and forth in the water behind his boat, while boy 2 is blowing air directly on his boat. Which of the boats will reach the other end of the tub first? Why?

​Figure 8.1

If you guessed that boy 1’s boat will reach the other end of the tub first, then you guessed right! This is because the water waves that boy 1 makes using his hand move his boat faster. Why is this so?

​Figure 8.1

Moving the boats from one end of the tub to the other requires energy from the boys. By blowing on his boat, boy 2 transfers his energy directly to the boat. Meanwhile, by moving his hand back and forth in the water, boy 1 transfers his energy to the water. This transfer of energy disturbs the water, producing waves. The waves carry the energy that boy 1’s boat needs to reach the other end of the tub faster than boy 2’s boat.

Classification of Waves

​Mechanical Waves

Mechanical waves are waves that require a medium to transfer energy from one point to another. An example of a mechanical wave is a flag swaying in the wind. It can be noticed how the flag’s fabric moves in waves as the energy travels along the flag.

Classification of Waves

​Mechanical Waves

Water waves, sound waves, and seismic (earthquake) waves are other examples of mechanical waves.

Water waves, such as ocean waves, require water to propagate. Sound waves are disturbances or vibrations that carry sound from one point to another through a solid, liquid, or gaseous material. Seismic waves, on the other hand, are waves of energy that travel through the surface and interior of the Earth.

Classification of Waves

​Electromagnetic Waves

Electromagnetic waves do not require a medium to transfer energy from one location to another. Because of this, electromagnetic waves can travel through space or in a vacuum as well as in solid, liquid, and gas. Electromagnetic waves that are given off by the sun reach Earth by traveling through space.

Classification of Waves

​Electromagnetic Waves

Examples of electromagnetic waves are radio waves, which enable radios and TVs to function. Other examples of electromagnetic waves are microwaves, infrared rays, visible light, ultraviolet rays, and gamma rays. All electromagnetic waves travel at the speed of light, which is 300 000 000 m/s.

Classification of Waves

​Electromagnetic Waves

However, they differ in their frequencies, and thus in their wavelengths too. Radio waves have the lowest frequency and thus have the lowest energy. Gamma rays, on the other hand, have the highest frequency, and thus have the highest energy.

Electromagnetic Waves