waves and sound - schools.misd.orgschools.misd.org/page/download/11856/0/shm waves student.pdf ·...

WAVES and Simple

Harmonic Motion

Add these words to the ovals in your

vocabulary frayer card packet

Vocab Quiz Tuesday 2/28

Packet due Monday 3/6amplitude

compressions

crest

diffraction

energy

frequency

interference

longitudinal

mechanical

medium

period

reflection

refraction

superposition

transverse

trough

wave

wavelength

Wave

A repeating and periodic disturbance that transfers energy from one place to another

WAVES TRANSPORT ENERGY NOT MATTER!!!

The particles in a wave vibrate however they do NOT move along with the wave, only the wave front itself moves on.

Pulse

a single non repeated disturbance

Mechanical Waves

Medium required to transfer energy

can be transmitted through solids, liquids, and gases.

they can not travel through space

Examples:

sound waves

water waves

Electromagnetic Waves

Medium NOT required to transfer energy

are able to transmit energy through a vacuum as well as solids, liquids, and gases.

They can travel through space

Examples: cosmic, gamma, x-ray, ultraviolet, visible light, infrared, microwave, radio (All waves on the EM Spectrum)

Types of Waves

Transverse

Compressional (Longitudinal)

Transverse Wave Diagrams

Transverse Wave Motion

Transverse Waves

Vibration is perpendicular (up & down)

to the direction the wave is moving. ex. light waves, snakey

Direction of Wave

Motion of Molecules

Longitudinal (compression)

Rarefaction

Compression Wavelength

Longitudinal Waves: Anatomy

Rarefaction: region in which the particles are spread out

Compression: region in which the particles are close together

A wavelength: composed of a complete rarefaction and a complete compression.

Longitudinal Wave Motion

Longitudinal (Compressional) Waves

vibration is parallel to the direction of

the wave. These waves require a

medium (such as air or water)

through which to travel.

ex. Sound waves (looks like a spring)

Direction of Wave

Direction of Movement

Calculating Wave Speed:

v = f

Where

v = wave speed in m/s

f = frequency in Hz

= the wavelength in meters.

Which wave has the longest

wavelength?

Which wave has the greatest

frequency?

What is the relationship between f and

λ when velocity held constant?

inversely related

IMPORTANT

The speed of the wave however depends solely on the medium through which a wave is traveling

Velocity of a Wave

The equation v=d/t can also be applied.

Energy and Amplitude

The rate at which energy is transferred by a wave depends on the _________ of the wave.

Energy of a wave IS NOT related to the speed of the wave.

amplitude

Which wave has greatest

amplitude?

Reflection

Reflection is the bouncing back of a wave at a boundary.

Examples of Reflection

Mirrors

Surface of water

A reflected sound wave is called an echo.

Refraction

Refraction is the change in speedof a wave at a boundary as it passes from one medium to another.

the wave “bends” or changes direction.

The speed changes however the frequency stays the same.

This means that the wavelength must change.

For refraction to occur,

Causing the wave to change speed & direction

The wave must enter a new medium (at an oblique angle).

Examples

Fish tanksWindows

Diffractionthe spreading of a

wavearound a barrier orthrough an opening.

The medium does not change!!!!!

In order for diffraction to occur, the opening or edge must be much smaller than the incident wave

These images are created by a ripple tank

Diffreaction Applications

Holograms (Not just depth, in it)

Flashlights

Waves at the marina

Double Slit Diffraction

Results in constructive and destructive interference

Interference

the result of the superposition of two or more waves, i.e. two or more waves occupy the same place at the same time.

constructive vs. destructive interference

Interference can be either constructive (build) or destructive (cancel).

Depends on how the waves overlap

Constructive interference

•waves align in sync or in phase

•displacement is in same direction

•Resultant wave has greater

amplitude than orignal waves

.

Destructive interference

•waves are out of sync(out of phase)

•displacement is in opposite direction

•Resultant wave has smaller amplitude than

orignal waves

•Total destruction if waves of equal amplitudes

meet 180O out of phase

node vs antinode

node: a point in a medium that is completely undisturbed when a wave passes.

Antinode: the point of maximum displacement; it can be either a crest or a trough

Standing Wave: A result of

interference

Created when two periodic waves of equal amplitude and wavelength travel in the opposite direction.

the nodes and antinodes of a wave are in a constant position.

as the frequency of the wave increases, the number of nodes and antinodes increases in the same amount of space.

Frequency and Period

T is period in seconds; time for one cycle to occur

f is frequency in Hz; how often one wave passes per second

f = # of occurrences T = time (sec)

time (sec) # of occurrences

Frequency and period are inversely related.

T=1/f f = 1/T

Periodic Motion

When a vibration or oscillation repeats itself over the same path

A specific form of periodic motion in which the restoring force is proportional to distance from the equilibrium position.

Simple _________ Motion (SHM):Harmonic

Objects that exhibit SHM

Spring Systems*

Pendulums*

Circular Motion

Waves

Sound, Light, Pressure

Period on a Spring

If we stretch a spring with a mass and release it, it will oscillate.

This is SHM!

What is the period of this

Motion?

Horizontal Springs

It has a mass of some kind attached to a spring.

This spring is stretched and released. This causes the entire system to oscillate. (move back and forth)

Hooke’s Law (force of a spring)

Fspring: magnitude of the distorting or restoring force in Newtons

K: spring constant or force constant (stiffness of a spring) in Newtons per meter (N/m)

x: displacement from equilibrium in meters

kxFS

If time

Simple harmonic motion - Physics Flash Animations

Period on a Spring

The period of a spring system is given by the equation below:

T – the period of motion

m – Mass of the body attached

k – spring constant

k

mTs 2

Period

What is the relationship between mass and period of a spring?

What is the relationship between spring strength (Think spring constant) and period of a spring?

Remember that period is always in seconds!

What is the difference between period and frequency?

Formulas

Calculating Period and Frequency

ond

cyclesf

cycles

ondsT

sec

sec

T = period or time for one revolution or cycle (sec)

f = number of revolutions or cycles per second (Hz or sec-1)

Let’s take a jump!

http://departments.weber.edu/physics/amiri/director/DCRfiles/Energy/bungee4s.dcr

https://www.youtube.com/watch?v=_iXlef9GFTY

Out of chaos, comes order. The scientific explanation notwithstanding , this is some neat stuff to watch

Harvard built a device with a series of fifteen pendulums in a row, each one of them slightly longer than its neighbor.

The pendulums were set into motion and the result was captured on video. The patterns that appear in this short video are fascinating to watch and to think about. Prepare to be captivated by this simple device !

Click on the below link but before starting the video, READ the complete explanation.Fascinating. I want one !

http://sciencedemonstrations.fas.harvard.edu/icb/icb.do?keyword=k16940&pageid=icb.page80863&pageContentId=icb.pagecontent341734&state=maximize&view=view.do&viewParam_name=indepth.html#a_icb_pagecontent341734

The Pendulum Formula

T = period (s)

l = length (m)

g = acceleration due to gravity (m/s2)

g

lTp 2

pendulum wave appletvibrating spring wave applet