Waves

What is a wave?

• Disturbance that travels from one location to another location

• Wiggle in time• Transfer of energy from one place to

another• Excitement of molecules in which particle

move, but are not transported• You make up your own……

Types of waves

• Mechanical – requires a medium for the transfer of energy– Two types – longitudinal and transverse

• Electromagnetic – do not require medium to travel. They can travel through a vacuum.– All EM radiation travels at the “speed of light” – 300,000,000 m/s, or 670,000,000 mph, 186,000

miles per second

Wave Words

• Medium – substance or material which carries the wave– Medium will affect the speed of the wave– Air, water, land, rock, string, metal– Speed of sound in: air 343 m/s, water 1482 m/s

steel 5960 m/s

More Wave Words

• Crest – section of the wave that rises above the undisturbed position

• Trough – section of the waves that dips below the undisturbed position

• Amplitude – maximum displacement of medium above the undisturbed position

• Wavelength – distance between two adjacent corresponding location on the wave (measure in meters)

Even more Wave Words

• Frequency – the number of waves which pass by in a given amount of time (measured in Hertz, cycles per second)

• Period – amount of time it takes for one wave to pass (measure in seconds)

Still more Wave Words

• Rarefaction – area of low pressure in a longitudinal wave– When molecules are most spread out

• Compression – area of high pressure in a longitudinal wave– When molecules are packed close together

Transverse Wave

• Particle move perpendicular (up and down) to motion of the energy

• Examples: ocean waves, S-waves, stadium “wave”

Parts of a Transverse Wave

San Andreas

Fault

Earthquake Body Waves

Primary “P” Waves• Longitudinal waves• Travel through liquid,

solid or gas• Fastest EQ waves

• 1.5 – 8 km/s

• Some animals can hear them, we feel them

• Not as destructive

Shear “S” Waves• Transverse waves• Travel through solids

only• Slower than P-waves• Tell us the mantle is

molten (liquid)

Seismograph –instrument which records the magnitude of an earthquake

Seismogram -– data or graph collected by the seismograph

[seismograph (graph) and seismometer (instrument) are also used and becomng the norm]

• Logarithmic scale used to measure the magnitude of an earthquake– 4.0 is 10x stronger than 3.0

• Microquake – less than 2.0, undetected by humans

• Moderate quakes are less than 6.0• Greatest recorded earthquake was 8.9

– 12/26/2004

Richter Scale

• 1990 – 6.2 on Ritcher Scale

• Occurred at subduction zone

• Sound is speeded up 50x

• Actual earthquake was 20 seconds

• Hear sharp P-waves first followed by louder S-waves

Longitudinal Waves

• Particle movement is parallel (back and forth) compared to direction of energy motion

• Examples: Sound waves, P - waves

• Compare types of waves

http://www.gmi.edu/~drussell/Demos/waves/wavemotion.html

• Play with frequency, amplitude

http://surendranath.tripod.com/Applets/Waves/Twave01/Twave01Applet.html