WAVES

Waves are rhythmic disturbances that carry energy without carrying matter. For example, water waves created by a boat make objects bob up and down, but the water molecules themselves don't travel outward — only the energy does.

Mechanical waves require matter (a medium) to transfer energy. They cannot travel through empty space. The medium can be a solid, liquid, or gas.

Sound waves are compressional (mechanical) waves. They are produced by vibrating objects. Your vocal cords vibrate to create them; the vibrating drumhead creates compressions and rarefactions in the air. Without a medium, sound cannot travel — this is why there is no sound in outer space.

Electromagnetic waves are transverse waves produced by electrically charged particles vibrating. Unlike mechanical waves, they do NOT need a medium — they can travel through a vacuum (outer space).

The amplitude of a transverse wave is the distance from the rest position to a crest or trough. For a compressional wave, amplitude is greater when particles are squeezed more tightly in compressions.

Amplitude = Energy: The greater the amplitude, the more energy the wave carries. Loud sounds have large amplitudes; bright light has large amplitudes. A hurricane's massive water waves have huge amplitudes and cause great destruction.

Wavelength is the distance between two adjacent crests (or two adjacent troughs) of a transverse wave. For compressional waves, it is measured from the center of one compression to the center of the next compression.

Different colors of light have different wavelengths — red light has a longer wavelength than green light, which has a longer wavelength than blue light.

Frequency is the number of wavelengths that pass a given point in 1 second. The unit of frequency is the hertz (Hz), named after German physicist Heinrich Hertz.

Frequency & Pitch: Higher frequency = higher pitch in sound. Higher frequency = color shifts toward blue/violet in light.

Wave speed depends on the medium through which it travels, not just the type of wave.

Reflection occurs when a wave strikes an object or surface and bounces off. The wave does not pass through or change direction by changing speed — it simply reverses.

Examples: echoes (sound reflecting off walls), seeing your face in a mirror or still pond.

Refraction is the bending of a wave as it moves from one medium into another at an angle, caused by a change in wave speed.

• A line perpendicular to the surface is called the normal.
• Light passing from air into water slows down and bends toward the normal.
• Light passing from water into air speeds up and bends away from the normal.
• The larger the speed change, the greater the bending.

Diffraction is the bending of waves around a barrier or through an opening. It is a property of waves, not particles.

Water waves diffract around islands. Radio waves diffract around buildings. This is why AM radio reaches farther around hills than FM.

Interference occurs when two or more waves overlap and combine to form a new wave. After the waves pass through each other, they continue as if nothing happened.