WAVES Chapter 15.

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WAVES Chapter 15

Objectives Explain how forces cause waves.
Explain how waves transfer energy. Classify wave types. Compare and contrast different wave types in an experiment.

A wave is a disturbance You experience waves everyday. Every sound you hear is a sound wave, every sight you see depends on light waves!

Check out this Wave... A Wave is a disturbance that transfers energy from one place to another. Waves can transfer energy over distance without moving matter the entire distance. For example: An ocean wave can travel many kilometers without the water itself moving many kilometers. Water moves up and down

Forces & Waves Forces can start a disturbance, sending a wave through a material. Rope Wave Water Wave

Earthquake Waves

Materials and Waves A rope tied to a doorknob, water, and the ground all have something in common. They are all materials through which waves move. A medium is any substance that a wave moves through. Like water or a rope

Mechanical Waves Waves that transfer energy through matter are known as mechanical waves. All the waves you’ve learned about so far are mechanical waves. An Earthquake wave is a good example of energy transfer.

Let's Try to Do ~THE WAVE~

Types of Waves Waves can be classified by how they move!
Some waves transfer an up-and-down or a side-to-side motion.

Transverse Waves Transverse Wave direction of disturbance
direction of wave transfer of energy ../Animations/wslm05_pg7_force.html

Longitudinal Waves Longitudinal Wave direction of disturbance
direction of wave transfer of energy

15.2 Properties of Waves Learn how to measure amplitude, wavelength, and frequency. Calculate a waves speed Collect data to investigate how to change frequency in an experiment.

How can Waves be Measured?
Height Speed Lengths Also known as: Amplitude Wavelength Frequency

Measuring Wave Properties
A crest is the highest point, or peak, of a wave. A trough is the lowest point, or valley, of a wave

E:\Animations\wslm05_pg18_graph.html water level at rest crest
fixed point crest trough E:\Animations\wslm05_pg18_graph.html

Amplitude Amplitude for a transverse wave is the distance between a line through the middle of a wave and a crest or trough. Amplitude is an important measurement because it indicates how much energy a wave is carrying.

Wavelength The distance from one wave crest to the next crest is called the wavelength. Can also be measured from trough to trough.

Frequency The number of waves passing a fixed point in a certain amount of time is called the frequency. It measures how often a wave occurs.

How Frequency and Wavelength are Related
When frequency increases more wave crests pass a fixed point each second. That means the wavelength shortens. So, as frequency increases, wavelength decreases. The opposite is also true. Look at picture on page 498

Graphing Wave Properties
The graph of a transverse wave looks like a wave itself The graph of a longitudinal wave looks like a spring of coils. Page 499

Measure Wave Speed The speed of any wave can be determined when both the frequency and the wavelength are known, using this formula: Speed= wavelength * frequency S= λ f Look at the example on page 501

Waves Travel Different types of waves can travel at very different speeds. Light waves travel through air almost a million times faster than sound. Example: Thunder and Lightening

Try This In a stormy sea, 2 waves pass a fixed point every second, and the waves are 10 m apart. What is the speed of the waves? S= λ f S= 10 m/wave * 2 wave/s = 20m/s

Review What two measurements of a wave do you need to calculate its speed? What is the top of a wave called? Bottom? What does the “Frequency” of a wave mean ?

15.3 Waves Behave in Predictable Ways
Describe how waves change as they encounter a barrier. Explain what happens when waves enter a new medium. Identify ways in which waves interact with one another.

Waves interact with materials
When waves interact with materials, they behave predictably. Scientist call these behaviors: Reflection, Refraction, and Diffraction.

Reflection The bouncing back of a wave after it strikes a barrier is called reflection. Water, sound & light waves all reflect.

Refraction Sometimes, a wave does not bounce back when it encounters a new medium. Refraction is the bending of a wave as it enters a new medium at an angle other than 90 degrees.

Diffraction You have seen how waves reflect off a barrier. For example, water waves bounce off the side of a pool. But what if the side of the pool had an opening in it? Diffraction is the spreading out of waves through an opening or around the edge of an obstacle. Occurs in all types of waves.

Diffraction Sound waves diffract as they pass through an open doorway.
Turn on a TV and then walk into another room. You can still hear it because the waves spread out.

Waves Interact with Other Waves
Interference is the meeting and combining of waves. The adding of two waves is called constructive interference. It builds up, or constructs, a larger wave out of two smaller ones. Page 507 Destructive Interference is when one wave attaches briefly to the trough of another wave. The energy of one wave is subtracted from the energy of the other. Page 508

Review Explain what happens when waves encounter a medium that they cannot travel through? Describe a situation in which waves would diffract. Describe two ways that waves are affected by interference.

TEST ON Friday, APRIL 30!!! STUDY