Chapter Twenty-Three: Waves

23.1 Harmonic Motion23.2 Properties of Waves23.3 Wave Motion

23.2 WavesA wave is an oscillation that travels

from one place to another.If you poke a floating ball, it oscillates

up and down.The oscillation spreads outward from

where it started.

Waves spread through connectionsA wave moves along a string because the string is continuous. By continuous we mean it is connected to itself.

Waves spread through connections.Anything that is continuous is said to be a medium for waves.

A medium is the “stuff” that waves travel through.

23.2 WavesWhen you drop a ball into water, some of the water is pushed aside and raised by the ball.

23.2 WavesWaves are a traveling form of energy because they can change motion.

Waves also carry information, such as sound, pictures, or even numbers.

23.2 Frequency, amplitude, and wavelength

You can think of a wave as a moving series of high points and low points.

A crest is the high point of the wave. A trough is the low point.

23.2 FrequencyThe frequency of a wave is the rate at which every point on the wave moves up and down.

Frequency means “how often”.

23.2 AmplitudeThe amplitude of a water wave is the maximum height the wave rises above the level surface.

23.2 WavelengthWavelength is the distance from any

point on a wave to the same point on the next cycle of the wave.

The distance between one crest and the next crest is a wavelength.

23.2 The speed of wavesThe speed of a water wave is how fast

the wave spreads, NOT how fast the water surface moves up and down or how fast the dropped ball moves in the water.

How do we measure the wave speed?

23.2 The speed of wavesA wave moves one

wavelength in each cycle.

Since a cycle takes one period, the speed of the wave is the wavelength divided by the period.

23.2 The speed of wavesThe speed is the distance traveled

(one wavelength) divided by the time it takes (one period).

We usually calculate the speed of a wave by multiplying wavelength by frequency.

• Water waves - Slow(2-3mi/h)

• Sound Waves - Decently Fast (660mi/h)

• Light waves - Extremely Fast (186,000mi/h)

Solving Problems

The wavelength of a wave on a string is 1 meter and its speed is 5 m/s.

Calculate the frequency and the period of the wave.

1. Looking for: …frequency in hertz …period in seconds

2. Given … = 1 m; s = 5 m/s

3. Relationships: s = f x or f = s ÷ f = 1/T or T = 1/f

4. Solution f = 5 m/s ÷1 m = 5 cycles/s T = 1/5 cycles/s = .2 s

Solving Problems

f = 5 HzT = .2 s