6.1 Wave Properties

SAS Curriculum Pathways Wave Properties

What happens if you drop a pebble into the water? Wave Motion What happens if you drop a pebble into the water? The disturbance created by the pebble generates water waves that travel away from the disturbance

Wave is the Motion of a Disturbance This disturbance causes water on the surface near that point to move, which in turn causes points farther away to move. In this way, the waves travel outward in a circular pattern away from the original disturbance.

Wave is the Motion of a Disturbance The water is the MEDIUM through which the disturbance travels. The medium does not actually travel with the waves. After the waves have passed, the water returns to its original position.

MECHANICAL WAVES = need MEDIUM Most of the waves (sound waves, spring waves…) need MEDIUM (air, water…)

MECHANICAL WAVES = need MEDIUM We call them MECHANICAL WAVES

ELECTROMAGNETIC WAVES = DO NOT need MEDIUM They can travel through vacuum

PULSE PERIODIC WAVE Wave Types Non – repeating wave Only single disturbance PERIODIC WAVE Repeating wave Period = recurring at regular intervals

Describing Waves

The highest point on the waves CREST The highest point on the waves

The lowest point on the waves Trough The lowest point on the waves

The distance between successive crests or troughs Wavelength The distance between successive crests or troughs

Amplitude The height of the wave

Frequency (f) measured in Hz How often the waves and their source vibrate per second (how many wavelengths per second)

Period (T) measured in seconds The time interval between vibrations (of the wavelength) Inverse of FREQUENCY

1.25 Hz 0.800 s 256 Hz 3.91 x 10-3s 0.25 Hz

Transverse Waves A wave whose particles vibrate perpendicularly to the direction of the wave’s motion. The spring is pulled sideways (up) while the pulse travels in the perpendicular direction (to the right)

Longitudinal Waves When several turns of the spring are compressed and let go The disturbance is in the same direction as the pulse will travel

Longitudinal Wave A wave whose particles vibrate parallel to the direction the wave is traveling

Wave REFLECTION When a wave encounters a boundary (shoreline, different medium…) and it is reflected back

The wave’s speed is changed AND it is BENT Wave REFRACTION When a wave hits a boundary at an angle OR the wave enters a new medium The wave’s speed is changed AND it is BENT

The Wave Equation Speed is equal to displacement divided by the time it takes to undergo that displacement For waves, a displacement of one wavelength (λ) occurs in a time interval equal to one period of the vibration (T).

The Wave Equation Because frequency and period are inversely related, Substituting this frequency relationship into the previous equation for speed gives a new equation for the speed of a wave.

Example 1: A piano string tuned to middle C vibrates with a frequency of 262 Hz. Assuming the speed of sound in air is 343 m/s, find the wavelength of the sound waves produced by the string.

200 Hz 1.5 m Practice Problems 6.1.1 If f doubles, λ is halved If f halves, λ is doubled 200 Hz 1.5 m

Answer the Concluding Questions

6.1 Review Questions (all)