Chapter 20 Section 1

Describe how waves transfer energy without transferring the matter.

Distinguish between waves that require a medium and waves that do not.

Explain the difference between transverse and longitudinal waves.

How many waves??

“Imagine that your family has just returned from a day at the beach. You had fun playing in the ocean under a hot sun. You put some cold pizza in the microwave for dinner, and you turn on the radio. Just then, the phone rings. It’s your friend calling to ask about homework.”

At least 5!!!!

“Imagine that your family has just returned from a day at the beach. You had fun playing in the ocean under a hot sun. You put some cold pizza in the microwave for dinner, and you turn on the radio. Just then, the phone rings. It’s your friend calling to ask about homework.”

Wave: any disturbance that transmits energy through matter or empty space

Energy can be carried away from its source by a wave

The material through which the wave travels does not move with the energy

Consider this…

As a wave travels, it does work on everything in its path

Work is done on the water and anything floating on it’s surface

Ex: Boats and docks bob up and down on the waves

The fact that the objects move tells us the waves are transferring energy

Medium: a substance through which a wave can travel

Most waves transfer energy by the vibration of particles in a medium

A medium can be a solid, liquid, or a gas

Energy is passed from particle to particle

Sound waves need a medium

Ocean waves need a medium

Waves that require a medium are called mechanical waves

Visible light, microwaves, radio waves, x-rays do not require a medium

These waves are called electromagnetic waves

EM waves can go through matter (air, water, glass….)

Energy that reaches the Earth from the Sun comes through EM waves, which go through space

Waves can differ in many ways

Classified based on:The direction in which the particles in the

medium vibrateDirection in which the waves move

2 Main Types of Waves:TransverseLongitudinal

Particles vibrate in a up-and-down motion

“moving across” or perpendicular to the direction the wave is going

Highest point of the wave: crest

Lowest point of the wave: trough

Electromagnetic waves are considered transverse

http://static.howstuffworks.com/gif/noise-canceling-headphone-7.jpg

Particles in the medium travel back and forth along the path that the wave moves

Where the waves are crowded together: compression

Where the particles are spread apart: rarefaction

Example: sound waves

http://static.howstuffworks.com/gif/noise-canceling-headphone-8.jpg

When a wave forms at the boundary of two media a transverse and a longitudinal wave combine to form a surface wave

Look like a transverse wave, but the particles of the medium move in circles

The particles move forward at the crest and backward at the trough

http://www.keele.ac.uk/depts/ma/euromech/rayleigh2.gif http://faculty.gvsu.edu/videticp/wave_animation1.GIF