GENERAL PROPERTIES OF WAVES INTRODUCTION TO WAVES

INTRODUCTION TO WAVES Throwing a pebble into a pond… Tsunami (26 Dec 2004)

What is a wave? Spreading of disturbance from one place to another. The source is a vibration or oscillation. Energy is transferred from one point to another WITHOUT physical transfer of any material between the two points

Two types of waves… Mechanical – waves that require a medium in which to travel Electromagnetic (EM) – do not require a medium – think light!

Two types of Mechanical waves: Type of Mechanical wave depends on the direction of the displacement of the wave itself. TRANSVERSE – displacement is perpendicular to starting position LONGITUDINAL – displacement is parallel to starting position

Comparing the two types:

THE WAVE GAME!!

ROPE WAVES Flash Animation of Rope Waves What do you observe about the wave motion? How is it similar to the human wave in the wave game?

Transverse Waves Transverse waves travel in a direction PERPENDICULAR to the direction of the vibrations.

Transverse Waves Some Examples: water waves rope waves electromagnetic waves (example: light)

Test Yourself! Rhonda sends a pulse along a rope. How does the position of a point on the rope, before the pulse comes, compare to the position after the pulse has passed?

The Slinky Coil What do you notice about the direction of the vibrations and the direction of the wave?

LONGITUDINAL WAVES Longitudinal waves travel in a direction PARALLEL to the direction of vibrations. Example: Sound

Longitudinal Waves Rarefactions are Where the coils/particles Spread out. Compressions are Where the coils/particles Are squeezed together.

Compression & Rarefactions

Challenge Describe how the fans in a stadium must move in order to produce a longitudinal stadium wave.

One more question…. A wave is transporting energy from left to right. The particles of the medium are moving back and forth in a leftward and rightward direction. What type of wave is this? What if the particles move upward and downward?

THE WAVE GAME!! Part 2

Crests and Troughs Crests: points of maximum displacement on a wave Troughs: points of minimum displacement on a wave displacement CREST Distance along rope TROUGH

AMPLITUDE (A) Maximum Displacement from the rest or central position. SI unit metre (m) displacement crest crest amplitude distance along rope amplitude trough

Wavelength (λ) The distance between two successive points of the same phase. Example: distance between two crests. SI unit: metre (m). displacement crest λ crest amplitude distance along rope amplitude trough

Parts on a Longitudinal Wave Think of compressions as the crests Think of rarefactions as the troughs

Frequency (f) Number of complete waves generated per second (or number of cycles/oscillations per second) SI unit: hertz (Hz)

Period (T) Time taken to generate one complete wave (or to complete one cycle) SI unit: second (s)

Relationship between T and f As f increases, T decreases

Putting everything together Try this!

SUMMARY

FOOD FOR THOUGHT In space films, we often hear the sound of the engine of the spaceship as the zoom past each other in outer space. We even hear the spaceship firing lasers at one another. What is seriously wrong in the films?

FOOD FOR THOUGHT Why don't incoming ocean waves bring more water on to the shore until the beach is completely submerged?

FOOD FOR THOUGHT How will the motion of water waves change as they move from deep to shallow water? How about from shallow to deep water? (Hint: Consider the speed of the waves)