PS 12-10

Waves

Objectives

• To recognize the relationship between waves and energy

• To distinguish between mechanical waves and electromechanical waves, and longitudinal and transverse waves

• Explain the relationship between particle vibration and wave motion

Connections

• What words precede the word wave?

• What do they have in common?

Connections

• Represent some sort of back and forth or up and down motion

• The coming and going of some condition

Does a floating object move with the ripple?

What is a wave?

• Is a disturbance that carries energy through matter or space

• It may or may not need a medium to move through, depending on the type of wave

Medium

• The matter through which a wave travels

• Examples, water, air, the Earth are all mediums

• Waves also pass through space, which is not a medium for the most part.

Mechanical waves

• Waves that require a medium

• Almost all waves are mechanical waves

• With one important exception

Light does not require a medium

• Electromagnetic waves do not need a medium

• Move by changing the electric and magnetic fields in space

• Light is the most widely known electromagnetic wave

Electromagnetic spectrum

• All use same method to travel

• All travel at the speed of light

Waves transfer energy

• We know waves transfer energy because they do Work

• Water waves boat, leaf, surfer…

• Sound waves eardrum

• Light waves on your eye, photographic film

Have you ever been hit by an ocean wave?

• Then you can get the idea that ocean waves can carry a lot of energy.

• Research is underway to find ways to harness energy of ocean waves

• Some of this research is being done at the university of Delaware

Energy from Ocean Waves

• June 2007

Wave Energy Bill Approved by U.S. House Science Committee

Washington, DC [RenewableEnergyAccess.com]

The U.S. House of Representatives Science and Technology Committee has approved, by voice vote, renewable energy legislation that would invest approximately $200 million

in federal funds to advance research and development of wave energy technologies

over the next four years.

Tsunamis

• Huge ocean wave

• Talk more about these in the Earth Science Section of this class

Wave Front

• Energy may spread out as a wave travels

• The waves spread out in circles that get bigger

• These circles are called wave fronts

• The energy of a wave front is constant– Gets spread out over a larger area – Less intense at any one point in a larger circle

Ripples

Why you hear• Notes from a singer result from the vocal cords in the throat moving

back and forth

• This move the particles in the air in the throat vibrate

• This vibration creates sound waves that eventually reach your ears

• The vibration of the air in your ears causes your eardrums to vibrate

• The motion of the eardrum triggers a series of electrical pulses to your brain

• Then your brain interprets them as sound

Vibrations

• Involve transformations of energy

• Potential to Kinetic and back

• Think of a weight on the spring

Simple harmonic motion

• Repetitive up and down motion

Damped Harmonic Motion

• The up and down motion fades over time

• Result of Friction, Air resistance or internal mechanisms

• Can be advantageous or not

• (How So?)