Objectives

Define wavesDistinguish between mechanical and electromagnetic waves

Distinguish between transverse and longitudinal waves

The Universe

Most of the universe can obviously NOT be directly measured!

An essential indirect measurement is necessary to study the universe - light. And to understand light, we need to understand waves.

Talk with your partner: What is a wave?

Waves

Wave = a disturbance that propagates (“moves”) through space and time.

Talk with your partner: Come up with as many things that travel in waves as you can.

WavesTwo kinds of waves. One difference involves a medium. Medium = matter or material.

Electromagnetic wave = electric/magnetic radiation. Does not need a medium. Includes radio waves, microwaves, X-rays, light.

Mechanical wave = an oscillation (movement) of matter. Does need a medium. Includes sound, ocean waves, seismic waves.

Mechanical Waves

Mechanical waves are easier for most people to visualize, so we’ll start there.

Slinky LabPlay with the slinky. Find and describe two different types of mechanical waves. Contrast them.

Compare them: describe ways that each of those two waves can vary.

Objectives

Distinguish between transverse and longitudinal waves

Identify the main five qualities or properties of wavesBe able to use the wave equations

Mechanical WavesTwo kinds of mechanical wavesTransverse wave = wave moves perpendicular to the direction of the energy.

Longitudinal wave = wave moves parallel to the direction of the energy.

QuickTime™ and a decompressor

are needed to see this picture.

Mechanical Waves

Mechanical waves are described in terms of these qualities: speed, frequency, period, wavelength, and amplitude.

Speed = the distancetraveled in a span oftime. (distance/time)

QuickTime™ and a decompressor

are needed to see this picture.

Mechanical Waves

The speed of a wave only depends on its medium.

You could not possibly make a slinky wave go faster or slower,

because the mediumis unchanged. QuickTime™ and a

decompressorare needed to see this picture.

Mechanical Waves

Frequency = How often the particles of a medium vibrate as the wave passes through. (cycles/time)

Frequency is measured in Hertz. 1 Hz = 1 cycle/second.

QuickTime™ and a decompressor

are needed to see this picture.

Mechanical Waves

Period = The time for a particle in a medium to make one complete vibration cycle. (time)

QuickTime™ and a decompressor

are needed to see this picture.

Mechanical Waves

Wavelength = The length of one wave cycle. (distance)

You’ll find that wavelength, frequency, and period are inseparable. A long wave naturally takes longer to happen, and thus happens less often.

QuickTime™ and a decompressor

are needed to see this picture.

Mechanical Waves

Amplitude = The maximum amount of displacement of a particle from its rest position. (distance) Crest = “Top” or “peak” of the wave

Trough = “Bottom” or “valley” of the wave

QuickTime™ and a decompressor

are needed to see this picture.

Mechanical Waves

Amplitude and wavelength can be easily confused.Wavelength = distance from crest to crest.

Amplitude = distance from crest to standstill, the place where the particle would be if there were no wave at all.

Waves

Without using your notes, answer these questions:

What are the two kinds of waves? What is the essential difference between them?

What are the two kinds of mechanical waves? What is the essential difference between them?

Wave Equations

Honors students must memorize these. College prep students need not, but must be able to use them in problems nevertheless.

Speed = Wavelength/Period Why is this? (Remember that speed = distance/time)

Speed = Wavelength x Frequency Recall that frequency = cycles/time

Midterm Info

Things you may bring to the midterm: At least two #2 pencils Your own calculator (recommended) A one page outline for the essay (I CANNOT PRINT IT FOR YOU)

The PLORNT grid, if you are doing essay #1

Things you will be provided with on the midterm: Calculator, unit conversions sheet (doesn’t include metric prefixes!), periodic table from textbook, vocabulary list (no definitions)

Midterm Info

Equations everyone needs to memorize:Density, percent error

Equations you will be provided if you are in College Prep:Specific gravity, both wave equations

Midterm Info

More info forthcoming on study strategies, format, etc.

Today is work time.Finish the homework first.Then start studying for the midterm.

Practice Problems

Which interval shows one full wavelength?

Which interval shows amplitude?

QuickTime™ and a decompressor

are needed to see this picture.

Practice Problems

Which interval shows one full wavelength? - A-E, B-F, or C-G

Which interval shows amplitude? A-B, B-C, C-D, D-E, E-F, F-G

QuickTime™ and a decompressor

are needed to see this picture.