New Standard • SPS9: Students will investigate the

properties of waves. – a. Recognize that all waves transfer energy.

b. Relate frequency and wavelength to the energy of different types of electromagnetic waves and mechanical waves. c. Compare and contrast the characteristics of electromagnetic and mechanical (sound) waves. d. Investigate the phenomena of reflection, refraction, interference, and diffraction. e. Relate the speed of sound to different mediums. f. Explain the Doppler Effect in terms of everyday interactions.

17.1:

Mechanical

Waves

What is a wave? • When matter is disturbed, energy comes

from the disturbance. This energy is in the form of a wave.

• A disturbance such as a pulse or shock produces a wave. – These disturbances are many times repeated or

periodic, such as a guitar string being struck. This makes the wave continuous

ALL WAVES TRANSPORT

ENERGY!

Mechanical Waves

Disturbance in matter that

carries energy from one place

to another

Mechanical Waves

• Created when a source of energy causes a vibration to travel through a medium.

• Requires a medium to travel through.

• Solids, liquids, and gases

• Classified by the WAY they move through a medium.

3 Main Types of Mechanical Waves

•Transverse waves

•Longitudinal waves

•Surface waves

Transverse Waves • Wave that causes the medium to vibrate at right angles to the direction in which the wave travels.

• The wave carries energy from left to right

• The highest point of the wave is the crest.

• The lowest point of the wave is the trough.

Transverse Waves Direction of wave

Crest

Rest position

Trough

Direction of vibration

Examples of Transverse Waves

• Ripples created when rock is thrown into water

• Rope tied to a tree

• Motion of a plucked guitar string

• Light waves…also called electromagnetic waves

• Secondary earthquake waves

Secondary Earthquake Waves

• Come after Primary Wave

• Cause the ground to roll

Longitudinal Waves • Waves in which the vibration of the medium is

parallel to the direction the wave travels.

• An area where the particles in a medium are spaced close together is called a compression.

• An area where the particles in a medium are spread out is called a rarefaction.

Longitudinal Waves

Examples of Longitudinal Waves

• Sound

• Primary earthquake waves

• Shock waves from an explosion

Surface Waves • Wave that travels along a

surface separating two media.

• Particles of the medium undergo a circular motion.

• Ocean waves are the most familiar kind of surface waves.

17.2: Properties

of Mechanical

Waves

Period • The time required for one complete

cycle to pass a particular point cycle is called the period.

1 Period

Frequency • The number of complete cycles in a given

time.

• Measured in cycles per second, or hertz (Hz).

•One hertz equals one wave cycle per second.

Frequency & Energy

Frequency & Energy have a Direct Relationship

High frequency=high energy

Low frequency=low energy

Wavelength • The distance between a point on one

wave and the same point on the next cycle of the wave.

–One wave cycle is equal to one wavelength.

Measuring Wavelength

Long wavelength Short wavelength

For a transverse wave, wavelength is measured between adjacent crests or between adjacent

troughs.

Measuring Wavelength

• For a longitudinal wave, wavelength is the distance between adjacent compressions or rarefactions.

Frequency & Wavelength

• Inverse relationship – Increasing the frequency of a wave decreases its

wavelength.

– Low frequency=Long wavelength

– High frequency=Short wavelength

Wave Speed • Formula:

Speed=Wavelength X Frequency • Units=meters per second

• Speed of a wave can change if it enters a new medium but for most waves the speed will remain constant.

Amplitude • The maximum displacement of the medium

from its rest position. – How high the wave rises.

– Intensity.

• Increase in amplitude means the wave carries more energy. – This is due to the fact that it takes more energy to

produce a larger wave.

– The more energy the wave has, the more the medium will be compressed or displaced.

Measuring Amplitude

Amplitude • Louder sounds have a greater amplitude.

• Brighter lights have a greater amplitude.