Unit 4: Pages 334 to 421 Chapter 8 in text Waves Unit 4: Pages 334 to 421 Chapter 8 in text

What do you already know? What is a wave? (where can you find this info…??? Where do we “see” waves in our everyday lives? Do we see all waves? Why are waves important to physicists? Create a list of as many waves you can think of in your everyday lives

Waves - Everyday Earthquakes Tsunamis Sound waves Radio waves Light waves*** Regular ocean waves Springs (Slinky!) car suspension

NOTE Light may or may not behave as a wave. There are two theories but light as a wave is the main theory… some physicists believe light behaves as a wave of electromagnetic radiation Other theory: Some physicists believe light is made of massless particles called photons not waves. Most physicists believe that light behaves as both… physics 12!!!

What is a wave (in physics)? Wave: a disturbance that transfers energy Whether ocean waves, waves on a string, earthquake waves, or sound waves in air, they all have a vibration as their source. Waves move large distances across the surface of a lake or the sea, yet the water itself does not travel those distances. Only the ENERGY!

Why are waves important to physicists? http://www.youtube.com/watch?v=TGaM8pdnr50&feature=related http://www.youtube.com/watch?feature=SeriesPlayList&v=XoYBAsHHXsk&list=PLFF513AD10F64B864 http://www.bing.com/videos/search?q=sinusoidal+wave%2c+classroom+demo+with+music&FORM=HDRSC3#view=detail&mid=CE19F9685E15A9EC09A9CE19F9685E15A9EC09A9 Waves are very important in engineering (buildings, bridges), seismology, etc. Waves explain how ENERGY MOVES.

Other Words for Wave Vibration Wiggle Oscillate

What do you need to cause a vibration? FORCE!

Summary Slide Wave: a disturbance that transfers energy Waves explain how ENERGY MOVES. Only the energy of a wave moves – not the material itself Waves are used in seismology, engineering, sound technology, light technology, radiation, solar energy, etc.

Summary Slide A wave needs a force to start and end. Waves are also called vibrations and oscillations.

Electromagnetic Waves An electromagnetic wave is a wave that is capable of transmitting its energy through a vacuum (i.e., empty space). Electromagnetic waves are produced by the vibration of charged particles. Example: Light waves Light travels through space (no medium) from the sun to Earth

All electromagnetic waves are transverse waves. http://www.youtube.com/watch?v=UHcse1jJAto

Transverse Waves… Transverse waves are when the displacement is perpendicular to the direction of the wave… Transverse waves are the ones most people can draw. Example. S waves (earthquakes), radiowaves, x-rays, and light waves (all electromagnetic waves)

Mechanical Waves A mechanical wave is a wave that requires a medium in order to transport energy from one location to another. Example: Sound waves

Question If waves need a medium, how does sound energy get transferred through the air?

Types of Waves There are three types of mechanical waves. 1. Transverse 2. Longitudinal 3. Surface

Longitudinal Waves… Longitudinal waves are when the displacement is parallel to the direction of the wave… Longitudinal waves travel through liquid (tsunamis) Example: P waves (geology), Sound waves, ultrasound waves

http://www.youtube.com/watch?v=Rbuhdo0AZDU http://www.gcse.com/waves/waves2.htm

Surface Waves A surface wave is a wave in which particles of the medium undergo a circular motion. They are typically in fluids (water or gas). Example: Water ripples on the surface of the pond

Questions for you! 1. A transverse wave is transporting energy from east to west. The particles of the medium will move_____. east to west only both eastward and westward c. north to south only d. both northward and southward

Answer: D The particles would be moving back and forth in a direction perpendicular to energy transport. The waves are moving westward, so the particles move northward and southward.

2. A wave is transporting energy from left to right 2. 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. This type of wave is known as a ____. A. Longitudinal B. Transverse

LONGITUDINAL!

In groups… 1) Create a transverse wave with a slinky. 2) Create a longitudinal wave with a slinky. 3) Create an organizational chart/diagram/Venn diagram to show the types of waves and an example of each.

Make a longitudinal wave with a slinky You produce a different wave when you move your hand backwards and forwards along the slinky. This sort of wave is a longitudinal wave. The particles carrying the wave in the slinky move backwards and forwards along the direction of wave motion.

Make a Transverse Wave using the slinky When using a slinky, move your hand from side to side some humps move away from you along the slinky. Although the waves move along the slinky, the movement of the slinky is side to side. This is a transverse wave. The particles carrying the wave in the slinky move at right angles to the direction of wave motion.

Bobbleheads… In groups… http://www.physicsclassroom.com/class/waves/u10l0a.cfm How does a bobblehead act like a “wave” or a vibration? How does the vibration start? Why does the vibration end?

Tuning Fork How does a tuning fork act like a “wave” or a vibration? How does the vibration start? Why does the vibration end?

Question Minute after minute, hour after hour, day after day, ocean waves continue to splash onto the shore. Explain why the beach is not completely submerged and why the middle of the ocean has not yet been depleted of its water supply.

Answer Ocean waves do not transport water. An ocean wave could not bring a single drop of water from the middle of the ocean to shore. Ocean waves can only bring energy to the shore; the particles of the medium (water) simply oscillate about their fixed position. As such, water does not pile up on the beach.

TRUE or FALSE: In order for John to hear Jill, air molecules must move from the lips of Jill to the ears of John.

FALSE! A sound wave involves the movement of energy from one location to another, not the movement of material. The air molecules are the particles of the medium, and they are only temporarily displaced, always returning to their original position.

3. Describe how the fans in a stadium must move in order to produce a longitudinal stadium wave. How would they make a transverse wave?

The fans will need to sway side to side The fans will need to sway side to side. Thus, as the wave travels around the stadium they would be moving parallel to its direction of motion. If they rise up and sit down, then they would be creating a transverse wave.

4. A science fiction film depicts inhabitants of one spaceship (in outer space) hearing the sound of a nearby spaceship as it zooms past at high speeds. Critique the physics of this film.

This is an example of faulty physics in film This is an example of faulty physics in film. Sound is a mechanical wave and could never be transmitted through the vacuum of outer space (no medium!)

Quick Review 1) What 2 things do ALL waves need? 2) What do mechanical waves need that electromagnetic waves don’t need? 3) What are the three sub-types of mechanical waves? Give an example of each. 4) Which of these sub-types is always an electromagnetic wave? Give an example of an electromagnetic wave.

Answers 1) Pulse/disturbance/force to start the wave and Energy 2) Mechanical waves need a medium to carry the energy from one point to another 3) Transverse (light), Longitudinal (sound), Surface (pebble dropped in a pond) 4) Transverse (light, xrays)