Essential Question?

• How does a wave transfer energy?

Waves• Wave – a disturbance that carries energy

through matter or space• For an example; • Ocean waves disturb water and transfer energy

through• During an earthquakes, energy transferred in

powerful waves that travel through the earth• Light is a type of wave that can travel through an

empty space from one place to another.

Wave – a disturbance that carries energy through matter or space

Mechanical waves –require a medium to travel through

Medium – something that something travels through

Sound travels through air, therefore, air is the medium.

Waves in a pond travel through water, therefore, water is the medium.

Waves1. You have learned how Newton's laws of

motion and principles of conservation of energy govern the behavior of particles.

2. These laws and principles also govern the motion of waves.

3. There are many types of waves that transmit energy even the ones you cannot see.

• Mechanical Waves - A mechanical wave is a disturbance that travels through some material or substance called the medium for the wave.

• Note: The medium as a whole does not travel with the wave.

• Note: A wave transfers energy, but it does not transfer any material or substance outward from the source.

Waves carry energy because they can do work.

Water waves can move an object up and down or throw it on a beach.

Sound waves move your eardrum and you hear.

Light waves allow your eye to see and can make an image on film.

Most waves are caused by a vibration.

Particles in a medium can vibrate either up and down or back and forth.

Waves are classified by the direction that the particles in the medium move as a wave passes by.

Wave Phenomenon

• Wave phenomenon, energy can move from one location to another, yet the particles of matter in the medium return to their fixed position. A wave transports its energy without transporting matter.

Two types of Waves• Transverse waves

• Longitudinal wave

2. Longitudinal wave – particles vibrate parallel to the direction of the wave motion

Sound Waves

• A sound wave traveling through air is a classic example of a longitudinal wave.

1. Transverse waves – particles move perpendicular to the motion of the wave

Transverse waves

• Waves in the electromagnetic spectrum are Transverse Waves

Parts of a Transverse Wave

Crest CrestWavelength

Trough TroughWavelength

Amplitude

Normal

Parts of a Wave

• Crest - each high point of a wave

• Trough – each low point

• Wave length – distance between points where the wave pattern repeats itself

• Amplitude – any periodic motion, the maximum distance an object moves from equilibrium

Parts of a Longitudinal

Wave

Compressions

Rarefactions

Rarefactions• Rarefactions - are regions of low air

pressure

Compressions

Rarefactions

Compressions • Compressions are regions of high air

pressure

Compressions

Rarefactions

The difference between Transverse and Longitudinal

waves

• Transverse waves -are those in which displacement of particle is perpendicular to that of propagation of wave.

• Longitudinal waves - are those in which displacement of the particle is in a direction parallel to that of propagation.

Period – In a periodic motion, the amount of time required for an object to repeat one complete cycle

Periodic motion- wave move up and down at the same rate

PERIOD

Example: 1 wave every 20 seconds

Frequency – The number of wave crest that pass a point during one second.

( expressed in hertz)

Example: 3 waves per Second (3Hz)

Frequency Equation

• The frequency of a wave length is equal to the reciprocal of the period

• F=1/T

Hertz

• The symbol for frequency is f.

• The SI unit is hertz (Hz).

• One vibration/wave per second is 1 Hz.

• Two vibrations/wave per second is 2 Hz.

Wave length Equation

• The wavelength of a wave is equal to the velocity divided by the frequency

• Wavelength = V/f

Period & Frequency

Depends on?

The source

Does Not depend on?

The medium and wave’s speed

What affects the waves speed?

The speed of a wave depends on the medium in which the wave is traveling.

Light waves can move through air faster than they can move through water. This is why a pencil will look broken when it is placed in a glass of water. Exactly where does the pencil look broken?At the junction of the two different mediums.

Sound travels faster in water than in air. Sound travels faster in solids than in liquids. Why do you think this is so?

The closer the molecules are, the easier it will be for the molecules to bump into one another. This allows the vibrations to move faster, thus allowing the wave to move faster.

Comparing Light & Sound Waves • Light waves can move through air faster than

they can move through water. Because?....• Once the Light Wave enters another medium it

changes directions and slows down. • Sound travels faster in water than in air.

Because?....• The closer the molecules are, the easier it will be

for the molecules to bump into one another. This allows the vibrations to move faster, thus allowing the wave to move faster.

Doppler Effect

Doppler effect – a change in the frequency of a wave when the source or observer is moving

Reflection

• bouncing back of a wave when it meets a surface

Refraction

• the bending of waves as they pass from one medium into another

Diffraction

• bending of waves as they pass through narrow openings or around sharp corners

Interference

• Interference – the combination of two or more waves that exist in the same place at the same time

Interference Waves

• Interference of light is difficult to observe since the waves are so small and the vibrations so rapid.

• However, interference takes place with any kind of wave motion, and the effects of interference can be more easily seen by the examining the behavior of water waves, which are in many ways similar to light waves, but travel more slowly and are more easily noticeable.

Constructive interference

Constructive interference – waves combine to make a larger wave

Destructive interference

• Destructive interference – waves combine to make a smaller wave

Interference – the combination of two or more waves that exist in the same place at the same time

Constructive interference – waves combine to make a larger wave

Destructive interference – waves combine to make a smaller wave

Review

• Mechanical waves (sound, ocean waves, seismic) require a medium (air, water, ground) to travel through.

Electromagnetic Waves

Electromagnetic waves – waves that are caused by a disturbance in electric and magnetic fields and does not require a medium to travel through

Electromagnetic waves are produced by the vibration of charged particles

Electromagnetic Waves

Electromagnetic Waves

• Electromagnetic waves are created by the vibration of an electric charge.

• This vibration creates a wave which has both an electric and a magnetic component.

• An electromagnetic wave transports its energy through a vacuum at a speed of 3.00 x 108 m/s (a speed value commonly represented by the symbol c).

Examples of electromagnetic waves:

Radio waves

Visible light waves

X-rays

Ultra-violet waves

Infrared waves

Microwaves

Lower energy

Longer wavelength

Higher energy

Shorter wavelength