A wave is a disturbance that transfers energy from one place to another. The key thing to remember is that waves move energy, not matter.

Think about a ripple spreading across a calm pond. A leaf floating on the surface will bob up and down as the ripple passes, but it won't be carried across the pond with the wave. The water molecules themselves are just moving locally, passing the energy along to their neighbors.

Waves can be sorted into two main categories based on what they travel through.

Mechanical waves need a substance, or medium, to travel. Sound is a classic example. It travels through the air as vibrations. Without air particles to vibrate, like in the vacuum of space, sound can't exist. Other examples include ocean waves traveling through water or seismic waves from an earthquake traveling through the Earth.

Electromagnetic (EM) waves are different. They don't need a medium at all and can travel through the vacuum of space. These waves are disturbances in electric and magnetic fields. Light from the sun, the microwaves that heat your food, and the radio waves that carry music to your car are all types of EM waves.

We can also classify waves by the direction of their disturbance. There are two types: transverse and longitudinal.

Imagine flicking one end of a rope up and down. You create a wave that travels along the rope's length, but each piece of the rope itself just moves up and down. Light and all other electromagnetic waves are transverse waves.

In a longitudinal wave, the particles of the medium vibrate parallel to the direction of energy transfer.

Think of a slinky. If you push one end, you'll see a compression travel down its length. The coils of the slinky move back and forth in the same direction the wave is traveling. Sound is a longitudinal wave, consisting of compressions (areas of high pressure) and rarefactions (areas of low pressure) in the air.

To describe waves, we use a few key properties. Let's look at a transverse wave to define them.

Finally, there's speed ($v$), which is simply how fast the wave's energy is moving through the medium. These three properties—speed, frequency, and wavelength—are all connected by a fundamental formula.

The speed of a wave is its frequency multiplied by its wavelength.

Here:

• $v$ is the wave speed (in meters per second, m/s)
• $f$ is the frequency (in Hertz, Hz)
• $\lambda$ is the wavelength (in meters, m)

This equation tells us that for a wave traveling at a constant speed, frequency and wavelength are inversely proportional. If the frequency goes up, the wavelength must go down, and vice versa.

These basic concepts are the building blocks for understanding all kinds of wave behaviors.