# characteristics of waves

## surface waves

A surface wave is a wave that travels along the surface of a medium. It combines a transverse wave and a longitudinal wave. Ocean waves are surface waves. They travel on the surface of the water between the ocean and the air. In a surface wave, particles of the medium move up and down as well as back and forth. This gives them an overall circular motion. This is illustrated in Figure 19.8 and at the URL below. MEDIA Click image to the left or use the URL below. URL: In deep water, particles of water just move in circles. They dont actually move closer to shore with the energy of the waves. However, near the shore where the water is shallow, the waves behave differently. They start to drag on the bottom, creating friction (see Figure 19.9). The friction slows down the bottoms of the waves, while the tops of the waves keep moving at the same speed. This causes the waves to get steeper until they topple over and crash on the shore. The crashing waves carry water onto the shore as surf.

## compressions and rarefactions

A longitudinal wave can be characterized by the compressions and rarefactions of the medium. This is illustrated in Figure 19.6. Compressions are the places where the coils are crowded together, and rarefactions are the places where the coils are spread apart.

## p waves

Earthquakes cause longitudinal waves as well as transverse waves. The disturbance that causes an earthquake sends longitudinal waves through underground rocks in all directions from the disturbance. Earthquake waves that travel this way are called primary, or P, waves. They are illustrated in Figure 19.7.

## mechanical waves

A mechanical wave is a disturbance in matter that transfers energy from place to place. A mechanical wave starts when matter is disturbed. An example of a mechanical wave is pictured in Figure 19.1. A drop of water falls into a pond. This disturbs the water in the pond. What happens next? The disturbance travels outward from the drop in all directions. This is the wave. A source of energy is needed to start a mechanical wave. In this case, the energy comes from the falling drop of water.

## the medium

The energy of a mechanical wave can travel only through matter. This matter is called the medium (plural, media). The medium in Figure 19.1 is a liquid the water in the pond. But the medium of a mechanical wave can be any state of matter, including a solid or a gas. Its important to note that particles of matter in the medium dont actually travel along with the wave. Only the energy travels. The particles of the medium just vibrate, or move back-and- forth or up-and-down in one spot, always returning to their original positions. As the particles vibrate, they pass the energy of the disturbance to the particles next to them, which pass the energy to the particles next to them, and so on.

## types of mechanical waves

There are three types of mechanical waves. They differ in how they travel through a medium. The three types are transverse, longitudinal, and surface waves. All three types are described in detail below.

## transverse waves

A transverse wave is a wave in which the medium vibrates at right angles to the direction that the wave travels. An example of a transverse wave is a wave in a rope, like the one pictured in Figure 19.2. In this wave, energy is provided by a persons hand moving one end of the rope up and down. The direction of the wave is down the length of the rope away from the persons hand. The rope itself moves up and down as the wave passes through it. You can see a brief video of a transverse wave in a rope at this URL: . To see a transverse wave in slow motion, go to this URL: (0:22). MEDIA Click image to the left or use the URL below. URL:

## crests and troughs

A transverse wave can be characterized by the high and low points reached by particles of the medium as the wave passes through. This is illustrated in Figure 19.3. The high points are called crests, and the low points are called troughs.

## s waves

Another example of transverse waves occurs with earthquakes. The disturbance that causes an earthquake sends transverse waves through underground rocks in all directions from the disturbance. Earthquake waves that travel this way are called secondary, or S, waves. An S wave is illustrated in Figure 19.4.

## longitudinal waves

A longitudinal wave is a wave in which the medium vibrates in the same direction that the wave travels. An example of a longitudinal wave is a wave in a spring, like the one in Figure 19.5. In this wave, the energy is provided by a persons hand pushing and pulling the spring. The coils of the spring first crowd closer together and then spread farther apart as the disturbance passes through them. The direction of the wave is down the length of the spring, or the same direction in which the coils move. You can see a video of a longitudinal wave in a spring at this URL: http

## instructional diagrams

No diagram descriptions associated with this lesson

## questions

You can start a surface wave by

``````a. pushing and pulling on a spring.

b. shaking a rope up and down.

-->  c. dropping a pebble in a pond.

d. all of the above
``````

What is required for a mechanical wave to occur?

``````a. a disturbance in matter

b. a source of energy

c. particles of matter

-->  d. all of the above
``````

The parts of a longitudinal wave where particles of matter are spread farthest apart are called

``````a. crests.

b. vibrations.

-->  c. rarefactions.

d. compressions.
``````

The lowest parts of a transverse wave is are known as

``````a. valleys.

-->  b. troughs.

c. bottoms.

d. media.
``````

What is an S wave?

``````a. any transverse wave

b. a type of longitudinal wave

-->  c. a wave generated by an earthquake

d. two of the above
``````

A mechanical wave starts with a disturbance in matter.

``````-->  a. true

b. false
``````

Particles of matter actually travel along with a mechanical wave.

``````a. true

-->  b. false
``````

Transverse waves travel only through solid matter.

``````a. true

-->  b. false
``````

Ocean waves travel deep below the surface of the water.

``````a. true

-->  b. false
``````

Earthquakes cause longitudinal waves.

``````-->  a. true

b. false
``````

The medium of a mechanical wave must be a solid or liquid.

``````a. true

-->  b. false
``````

In a surface wave, particles of the medium move only up and down.

``````a. true

-->  b. false
``````

Ocean waves crash on shore when the bottoms of the waves slow down due to friction.

``````-->  a. true

b. false
``````

In a surface wave, particles of matter move in a circular motion.

``````-->  a. true

b. false
``````

All waves transfer energy from one place to another.

``````-->  a. true

b. false
``````

A primary (P) wave is a longitudinal wave.

``````-->  a. true

b. false
``````

All waves must travel through matter.

``````a. true

-->  b. false
``````

All mechanical waves are either transverse or longitudinal waves.

``````a. true

-->  b. false
``````

Some waves do not require a medium.

``````-->  a. true

b. false
``````

A source of energy is needed to start a mechanical wave.

``````-->  a. true

b. false
``````

disturbance in matter that transfers energy from place to place

``````a. longitudinal wave

b. trough

-->  c. mechanical wave

d. medium

e. surface wave

f. rarefaction

g. transverse wave
``````

part of a longitudinal wave where particles of the medium are spread farthest apart

``````a. longitudinal wave

b. trough

c. mechanical wave

d. medium

e. surface wave

-->  f. rarefaction

g. transverse wave
``````

wave in which particles of the medium vibrate at right angles to the direction that the wave travels

``````a. longitudinal wave

b. trough

c. mechanical wave

d. medium

e. surface wave

f. rarefaction

-->  g. transverse wave
``````

combined transverse and longitudinal wave

``````a. longitudinal wave

b. trough

c. mechanical wave

d. medium

-->  e. surface wave

f. rarefaction

g. transverse wave
``````

part of a transverse wave where particles of the medium are lowest

``````a. longitudinal wave

-->  b. trough

c. mechanical wave

d. medium

e. surface wave

f. rarefaction

g. transverse wave
``````

wave in which particles of the medium vibrate in the same direction that the wave travels

``````-->  a. longitudinal wave

b. trough

c. mechanical wave

d. medium

e. surface wave

f. rarefaction

g. transverse wave
``````

matter through which a mechanical wave travels

``````a. longitudinal wave

b. trough

c. mechanical wave

-->  d. medium

e. surface wave

f. rarefaction

g. transverse wave
``````

Types of mechanical waves include

``````a. longitudinal waves.

b. transverse waves.

c. surface waves.

-->  d. all of the above
``````

The medium of a mechanical wave can be a

``````a. gas.

b. solid.

c. liquid.

-->  d. any of the above
``````

The crests of a transverse wave are like the

``````a. crests of a primary wave.

b. troughs of a longitudinal wave.

c. rarefactions of a secondary wave.

-->  d. compressions of a longitudinal wave.
``````

Examples of mechanical waves include all of the following except

``````a. ocean waves.

b. sound waves.

c. waves in a rope.

-->  d. electromagnetic waves.
``````

Waves that an earthquake sends through rocks underground include

``````a. tsunami waves.

b. transverse waves.

c. longitudinal waves.

-->  d. two of the above
``````

Which of the following statements about ocean waves is true?

``````-->  a. They travel on the surface of the water.

b. They travel deep underwater.

c. They are secondary waves.

d. They are primary waves.
``````

You generate a longitudinal wave when you

``````a. shake a spring up and down.

b. shake a rope up and down.

-->  c. push and pull a spring.

d. two of the above
``````

## diagram questions

No diagram questions associated with this lesson