Chapter 15.1 - Types of Waves

15.1 Types of Waves

What does a wave carry?

How are waves generated?

What is the difference between a transverse wave and a longitudinal wave?

How do the particles in ocean waves move?

A wave is a disturbance that carries energy through matter or space.
Two main types of waves:
- Mechanical Waves: Require a medium to travel through.
- Electromagnetic Waves: Do not require a medium.

A medium is a substance that allows energy to travel through waves.
- Example: Water for ocean waves, air for sound waves, earth for earthquakes.

Mechanical Waves:
- Require a medium.
- Examples: Sound waves, ripples in a pond, earthquakes.
Electromagnetic Waves:
- Do not require a medium.
- Consist of changing electric and magnetic fields in space.
- Examples: Light, radio waves.

Waves carry energy because they can do work.
- Example 1: Water waves moving a leaf or boat.
- Example 2: Sound waves affecting the eardrum.
Energy: The ability to exert a force over a distance, or to do work.
The bigger the wave, the more energy it carries.
- Example 1: Dropping a stone in a pond creating a wave that moves a leaf several centimeters.
- Example 2: A cruise ship creating waves that move a fishing boat a few meters.
Tsunamis:
- Huge ocean waves caused by earthquakes.
- Can be as high as 30 m (taller than a 10-story building).
- Carry enough energy to cause significant damage to coastal towns.
Normal ocean waves break rocks into sand.

Energy may spread out as a wave travels.
- Sound waves from a concert speaker can be harmful up close but harmless at a distance.
Wave Front:
- Circles that get bigger as waves move from the center.
- Each wave front carries the same amount of energy, but the energy is spread out over a larger area in larger circles.
As waves travel outward, spherical wave fronts get bigger, and energy spreads over a larger volume.

Most waves are caused by vibrating objects.
- Example: A singer's vocal cords vibrate, creating sound waves.
- The vibration of air in the ears causes eardrums to vibrate, triggering electrical pulses to the brain, which interprets them as sounds.
Electromagnetic waves may be caused by vibrating charged particles.
In mechanical waves, particles in the medium also vibrate.

Waves are classified based on the direction in which particles in the medium move.
- Transverse Waves
- Longitudinal Waves

A transverse wave is a wave in which the wave motion is perpendicular to the particle motion.
Movement of particles is at a 90-degree angle to the direction the wave is traveling.
Electromagnetic waves (light, radio waves, X-rays) are transverse waves.
Electric and magnetic fields move perpendicular to the wave's direction.
- Electric Field (E): Moves up and down.
- Magnetic Field (B): Moves side to side.
- Wave Direction: Moves forward.
Crests: High points of a transverse wave.
Troughs: Low points of a transverse wave.

A longitudinal wave is a wave in which the wave motion is parallel to the particle motion.
Sound waves are longitudinal waves.
Sound waves compress and expand air in bands.
Air molecules move backward and forward, parallel to the direction of the sound waves.
Longitudinal waves do not have crests and troughs.
Compressions: Crowded areas in a longitudinal wave.
Rarefactions: Stretched-out areas in a longitudinal wave.

Waves on the ocean or in a swimming pool are not simply transverse or longitudinal waves; they are surface waves.
Particles in a surface wave move both perpendicularly and parallel to the direction in which the wave travels.
Surface waves occur at the boundary between two different mediums, such as water and air.
Water molecules move in circular or elliptical paths as the wave passes.

Step-by-step motion of a beach ball on water:

Starts in a trough (low point):
- The ball moves to the left (the wave pulls it back).
- The ball also starts to move upward as the wave rises.
Reaches the crest (high point):
- The ball moves to the right (the wave is pushing it forward).
- The ball is now at its highest point.
After the crest passes:
- The ball falls downward as the wave lowers.
- It also moves to the left again.
Back to the starting position:
- The whole process repeats, making the ball move in an elliptical (almost circular) motion.

Water waves have both transverse (up & down) and longitudinal (back & forth) motion.
These two motions combine to create a circular movement of water molecules and anything floating on the surface.