Mr' Perez

1
Mr. Perez

• Grade 6 Science
• Speed of Sound, Echoes, Echolocation,
  Instruments, and The Doppler Effect

2
Speed of Sound

• The speed of sound in the air is about 340 m/sec
• The speed of sound is much slower than the speed
  of light (300,000,000 m/sec)
• The speed of sound in water is about 1,500 m/sec
• Why do you hear thunder after you see lightning?
• The light from the thunder travels much faster
  than the sound of the thunder

3
Speed in Different Materials
4
Faster than Sound

• Supersonic speed is faster than the speed of
  sound
• Some airplanes can travel two or three times
  faster than the speed of sound
• You can see these planes fly overhead before you
  can hear them
• Mach number is the speed of an object moving
  through air (or any liquid) divided by the speed
  of sound through the substance
• Sonic booms produce loud noises that can break
  glass

1947 - Chuck Yeager became the first man to fly
faster than Mach-1 on the Glamorous Glennis
5
What Is an Echo?

• When a sound wave is reflected, the reflected
  sound is called an echo
• Reflection is the bouncing back of a wave from a
  barrier that doesnt absorb its energy
• Sound will reflect off of wood floors, brick,
  glass, concrete, high ceilings, large rooms, etc.
• Carpeting is used to stop sound waves from
  bouncing around a room
• Why? Carpeting absorbs the sound waves
• Acoustics are the qualities that determine the
  ability of a room to reflect sound waves that
  produce distinct hearing. Padding can be added
  or removed.

6
Echolocation

• Bats give off high pitched sounds to see and fly
  in the dark
• These sounds reflect off of surrounding objects
• With their sensitive ears, the bats can locate
  insects from the echoes they give off
• Bats also use echoes to communicate with other
  bats

• Dolphins and whales also give off high pitched
  sounds
• These sounds are reflected from objects in the
  ocean
• They can use echoes to communicate over long
  distances
• Why? Because sound travels faster in water than
  air
• Whales and dolphins catch food this way

7
SONAR

• SONAR stands for SOund Navigation And Ranging
• SONAR can be used to map the ocean floor, locate
  ships and wreckage, and find schools of fish
• Sound waves are sent from a ship to the bottom of
  the ocean (or an object)
• The time the sound takes to reach the bottom of
  ocean (or object) and bounce back as an echo is
  measured
• The time is then divided in half to find how long
  the sound took to go one way
• The speed of sound travels through water at a
  speed of 1,500 m/sec

8
SONAR - Problem Solving

• A SONAR signal is sent from a research ship to
  the bottom of the ocean. The echo returns 6
  seconds later. How deep is the ocean at that
  spot?
• 1st Divide by two to find half of the total
  number of seconds that was sent from the ship AND
  back to the ship
• 2nd Multiply by 1,500 m/sec because that is how
  fast sound travels in water
• 3rd Your answer is the depth, and the unit is
  meters.
• 6 seconds ? 2 ? 3 sec
• 1,500 m/sec ? 3 sec
• The ocean depth is 4,500 m

9
SONAR - Problem Solving

• A SONAR signal is sent from a ship to a whale in
  the ocean. The echo returns to the ship 8
  seconds later. How deep is the whale at that
  spot?
• 8 seconds ? 2 ? 4 sec
• 1,500 m/sec ? 4 sec
• The whale is 6,000 m below the ship
• A SONAR signal is sent from an aircraft carrier
  to an enemy submarine below it. The echo returns
  to the ship 14 seconds later. How deep is the
  submarine?
• 14 seconds ? 2 ? 7 sec
• 1,500 m/sec ? 7 sec
• The submarine is 10,500 m below the aircraft
  carrier

10
Ultrasound

• Ultrasound is similar to SONAR, but it can be
  used to see inside solid objects (and people)
• Ultrasound uses high pitched sounds (greater than
  20,000 Hz)
• Most of the sounds pass through the objects, but
  some are reflected back
• These echoes produce an image on a screen,
  similar to an x-ray

11
The Doppler Effect

• The frequency of sound waves changes as the
  source of the waves move towards you
• The waves are pushed close together as a moving
  object moves towards you, and it appears to have
  a high frequency. The shorter wavelengths give a
  higher pitch.
• As the object passes you, the sound waves spread
  out and the object appears to have a low
  frequency. The longer wavelengths give a lower
  pitch.
• This is the Doppler Effect.

• Train Passing
• Car Passing
• Motorcycle Passing
• Stampede

12
Warm Air and Cold Air

• Sound travels faster through warm air (than cold
  air)
• Why? Because the molecules in warm air are
  colliding faster than in cold air, and sound
  needs collisions of molecules to travel. More
  collisions faster sound travel.
• Sound travels faster through humid air (than dry
  air)
• Why? Humidity is the amount of water vapor in
  the air. The more humid the air, the faster
  sound will travel.
• Sound travels slower with increasing altitude
• Why? Because there is usually a temperature
  decrease the further you get from the surface of
  the Earth. Lower temperatures mean slower sound
  travel because the molecules in cool air are not
  colliding as fast as warm air.

13
Sound Samples - Hertz

• H\Sound Unit\50Hz.wav
• H\Sound Unit\100Hz.wav
• H\Sound Unit\1000Hz.wav
• H\Sound Unit\10000Hz.wav