Energy on the Move
What do an ocean wave, the sound from a guitar, and the light from the sun all have in common? They are all waves. In science, a wave is a disturbance that transfers energy from one place to another.
The key idea is that waves transfer energy without transferring matter. An ocean wave can travel across the entire sea, but the water molecules themselves mostly just bob up and down in place.
Mechanical vs. Electromagnetic Waves
There are two main categories of waves.
Mechanical Waves: These are waves that require a medium (a substance) to travel through. The wave is a vibration of the particles of the medium.
Examples: Sound waves (traveling through air), ocean waves (traveling through water), the wave on a rope you shake.
Mechanical waves cannot travel through a vacuum (empty space). This is why there is no sound in space.
Electromagnetic (EM) Waves: These are waves that do not require a medium. They are disturbances in electric and magnetic fields and can travel through the vacuum of space.
Examples: Light, radio waves, microwaves, X-rays.
Transverse vs. Longitudinal Waves
We can also classify waves by the direction of their vibration.
Transverse Waves: In a transverse wave, the particles of the medium vibrate perpendicular (at a right angle) to the direction the wave is traveling.
Imagine shaking a rope up and down. The wave moves horizontally along the rope, but the rope itself moves vertically.
Key parts: The highest point of a transverse wave is a crest, and the lowest point is a trough.
Examples: Light and all other EM waves, waves on a string.
Longitudinal Waves: In a longitudinal wave, the particles of the medium vibrate parallel to the direction the wave is traveling.
Imagine pushing and pulling a Slinky. The wave is a series of scrunched-up parts and stretched-out parts that moves along the Slinky.
Key parts: The scrunched-up parts are called compressions, and the stretched-out parts are called rarefactions.
Example: Sound waves.
Properties of a Wave
We can describe any wave using four basic properties:
1.Amplitude: The maximum distance the particles of the medium move from their rest position. It's the 'height' of the wave. A wave with a large amplitude carries more energy. For sound, this is loudness; for light, this is brightness.
2.Wavelength (λ): The distance between two corresponding parts of a wave, for example, from one crest to the next crest, or from one compression to the next.
3.Frequency (f): The number of complete waves that pass a given point in a certain amount of time. It is usually measured in Hertz (Hz), where 1 Hz is one wave per second.
4.Speed: How fast the wave is traveling. The speed of a wave is related to its frequency and wavelength by the formula: Speed = Wavelength × Frequency.