What are sound waves and light waves, what medium do they need, are they mechanical waves, what media do seismic waves travel through, what is a wavefront, what does sound frequency determine, and what determines loudness?

Answer

Sound waves are mechanical longitudinal waves that require a material medium (solid, liquid, or gas), while light waves are electromagnetic waves that do not require a medium and can travel through a vacuum. Seismic waves travel through Earth materials: P-waves through solids, liquids, and gases; S-waves only through solids; surface waves along solid surfaces. A wavefront is an imaginary surface (or line in 2D) connecting points on a wave that are in the same phase, such as all crests at a given instant. Sound frequency determines pitch, and loudness is mainly determined by wave amplitude (sound intensity, measured in decibels).

Explanation

What you are being asked about

These questions connect a few core wave ideas: what type of wave something is (mechanical vs electromagnetic), whether it needs a medium, and how wave properties like frequency and amplitude relate to what we hear.

Sound waves vs light waves (type of wave and medium)

Sound wave: a mechanical wave, usually longitudinal in air. It is a vibration of particles in a material, so it must have a medium.
It can travel through solids, liquids, and gases, but not through a vacuum.
Light wave: an electromagnetic wave and it is transverse.
It does not require a medium and can travel through a vacuum (space).

What media do seismic waves travel through?

Seismic waves are mechanical waves produced by earthquakes and explosions. There are different types:

P-waves (primary waves) are compressional (longitudinal) and can travel through solids, liquids, and gases.
S-waves (secondary waves) are shear (transverse) and can travel through solids only (they do not pass through liquids).
Surface waves travel along the Earth’s surface, which is solid.

What a wavefront means

A wavefront is a set of points on a wave that are at the same phase.

Example: if you freeze time, every point on a crest is in phase with every other point on that crest. The curve (or surface) joining those points is a wavefront.
For a point source, wavefronts are often circular (2D) or spherical (3D).

Frequency and pitch

For sound, frequency $f$ determines pitch:

Higher $f$ means higher pitch.
Lower $f$ means lower pitch.

What makes sound louder

Loudness mainly depends on amplitude of the sound wave, which is related to intensity.

Larger amplitude means more energy carried by the wave and a louder sound.
Loudness is commonly reported using the decibel (dB) scale, which is based on intensity.

Skills You Achive

wave classification sound physics seismology basics frequency and amplitude electromagnetic waves