What is a wave? A disturbance that moves through matter or space.

Energy moving from place to place.

The matter or space that the wave travels through is called a medium

Classification of waves There are two main categories of waves:

1. Mechanical Waves (our focus now )

~ Require a medium in order to transport their energy from one location to another.

~ Ex: Sound

2. Electromagnetic Waves (we will look at these in more detail next week)

~ EM waves are capable of transmitting energy through a vacuum (i.e., empty space).

~ Ex – Photons of light

Mechanical Waves Two types of waves:

1. Longitudinal (aka Compressional)

•Longitudinal waves look like a slinky•Direction of medium is parallel to the direction of wave propagation (motion)•Ex: Sound Waves - move air back and forth

Characteristics of a Longitudinal Wave

2 areasCompression- an area of high molecular density and pressureRarefaction - an area of low molecular density and pressure

Mechanical Waves Two types of waves:

2. Transverse

•Transverse waves look like a sine curve•Direction of medium is perpendicular to direction of wave propagation (motion)•Ex: Water Waves - move stick up and down in a pond

Characteristics of a Transverse Wave1)Crest- highest position

of the wave2) Trough- lowest

position of the wave

3) Wavelength- the distance between two ‘like’ points on a wave(crest to crest; trough to trough)

4) Amplitude- Height of the wave (from origin to crest or trough)

5) Frequency- The number of crests that pass by a point each second.

Crest

Trough

Measuring a Wave

Frequency is how many waves pass by you (or an arbitrary point) per second, measured in Hertz.

Period is the number of seconds (usually it’s less than 1 second) it takes for 1 WAVE to pass by you, measured in seconds or seconds per wave.

Tf

1

fT

1

Frequency vs. Period

Measuring a Wave Wave motion compared to linear motion

Wavelength is comparable to displacement

Period is comparable to time

To find linear speed you use the equation:

To find wave speed do the same thing, just with wave variables:

Since frequency is the inverse of period you will usually see the equation : wave speed = wavelength x frequency

Units: Since a “cycle” is not a standard unit this gives you m/s.

time

distancespeed

)(period

)( wavelength(v)speed wave

f v

Stan and Anna are conducting a slinky experiment. They are studying the possible affect of several variables upon the speed of a wave in a slinky. Their data table is shown below. Fill in the blanks in the table.

Medium Wavelength Frequency Speed

Zinc,

1-in. dia. coils1.75 m 2.0 Hz ______

Zinc,

1-in. dia. coils0.90 m 3.9 Hz ______

Copper,

1-in. dia. coils1.19 m 2.1 Hz ______

Copper,

1-in. dia. coils0.60 m 4.2 Hz ______

Zinc,

3-in. dia. coils0.95 m 2.2 Hz ______

Zinc,

3-in. dia. coils1.82 m 1.2 Hz ______

(1.75)(2)= 3.5m/s

(0.9)(3.9)= 3.51m/s

(1.19)(2.1)= 2.499m/s

(0.6)(4.2)= 2.52m/s

(0.95)(2.2)= 2.09m/s

(1.82)(1.2)= 2.18m/s