7th grade Notes Week 17-Monday

Waves Intro

Waves Intro: what it is…

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A wave is a disturbance caused by a forceExample: you drop a pebble in water, a wave is formed

Waves: What do they do?C-notes

Waves transfer ENERGYThe molecules of the MEDIUM do NOTMove to another place…

Waves Intro: Causes & Examples

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a)Water waves…caused by wind (some by Earthquakes- tsunami)

b)Ground shakes because pressure is released (EARTHQUAKE)

c)You hit something it vibrates making a sound. Sound moves in waves

Waves Intro: Types of waves

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There are two types of waves:Mechanical and Electromagnetic

Waves Intro: Mechanical

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Mechanical waves are waves that move in MATTER.If there is no “MATTER”; there is no movementMEDIUM- is any type of matter that mechanical waves move in

Mechanical Wave: An example

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•Sound is an example of a mechanical wave.•Sound is produced by vibrations•The energy from the vibration moves in waves•Sound can ONLY travel if there is a medium

Waves Intro: Electromagnetic

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Electromagnetic waves can move through “empty” space. A place with little or no molecules is called a vacuum

Parts of a Transverse wave

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Crest- highest point of the wave

Trough (troff)- lowest point of the wave

REST LINEIf there were no energy…

Types of mechanical waves

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Transverse waves are waves in which the movement of the vibrating particles is perpendicular to the direction of the wave.Example:Water wave

Types of mechanical waves

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Longitudinal waves are waves in which the movement of the vibrating particles is parallel to the direction of the wave.Example: sound wave

Properties of (ALL) Waves

Frequency:How many crests pass in a second

Amplitude:Measure from rest line to crest

Wavelength:Measure from one crest to the next

AmplitudeWhat does it measure?

Diagram of what it measures

Wavelength What does it measure?

Diagram of what it measures

Frequency What does it measure?

Diagram of what it measures

The energy of the wave.The more amplitude the more energy.

The distance between one crest and another

The number of vibrations (waves) each second.Unit used: hertz

Sound Energy C-notes

Sound energy is the energy of vibration

Sound produces an mechanical wave- it needs a medium to move in

Sound Energy C-notes

Sound waves are LONGITUDINAL waves

Another name for longitudinal waves is a COMPRESSION wave

Sound Energy C-notes

Sound waves have the same properties as waves (amplitude, wavelength, frequency)However there are two “parts” to a COMPRESSION wave

Sound Energy C-notes

Compression- where molecules of medium and pressed together

Rarefaction- where molecules of a medium spread apart

Hearing and Wave properties

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Our ears can sense the amplitude of a sound wave

The more energy, the more amplitude.

Hearing and Wave properties

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The greater amplitude is sensed as INTENSITY (LOUDNESS)

The sound intensity is measured with a unit called decibel

Hearing and Wave properties

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Our ears can sense frequency of the vibration

The more vibrations, the higher the frequency. This is a high pitch sound

Hearing and Wave properties

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Our ears can sense frequency of the vibration

The more vibrations, the higher the frequency. This is a high pitch sound

Hearing and Wave properties

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Frequency is measured in a unit called HERTZ (Hz). These are vibrations per second

We can “hear” 20 hertz to 20,000 hertz