What is the difference between noise and music? Warm-UP Activity 2/25/09 What is the difference between noise and music?

Let’s check our sound facts! SOUND WAVES Let’s check our sound facts!

Originate from vibrating objects. SOUND WAVES Originate from vibrating objects.

SOUND WAVES The vibrating objects transfer this sound energy by direct contact with other matter (usually air).

SOUND WAVES Sound waves are classified as mechanical waves and they require a medium to transfer the energy.

SOUND WAVES The energy disturbance travels in concentric waves, spreading out from the source like ripples that spread out when a pebble is dropped in a puddle.

Sound waves are compressional or longitudinal waves.

Sounds from a Stereo Speaker

SOUND WAVES As sound waves move in a medium, the particles of the medium move back and forth in the same direction that the sound wave itself is traveling.

Speed of sound waves depends on Type of medium Temperature of the medium Sound Wave speed VS. Light wave speed

Speed of sound waves depends on Type of medium: Liquids and solids transmit sound waves better than gases The particles are closer together in liquids and solids making the transmission of energy easier

Speed of sound waves depends on Temperature of medium: Higher temperature -- faster speed Sound will travel slower in cold air on a winter’s day than it will travel in the warm air of a summer’s day

Sound waves speed vs. light speed Sound travels slower than light:  Sound travels at 344 m/s through air at 200 C  Light travels at 300,000,000 m/s

Sound Wave Fact #7 Force vibrations occur when an original vibrating object is put in contact with another object (which can also vibrate).

Sound Wave Fact #7 The first object makes the second object vibrate at the same speed or frequency.

Sound Wave Fact #7 If the second object has a greater surface area than the first, then it causes a greater amount of air to also vibrate at the original frequency.

Sound Wave Fact #7 The larger surface area creates a bigger sound wave. Therefore, the waves reaching your ears are larger and you perceive the sound as louder.

Can you explain why the flash of a firework is seen before the sound of the firecracker explosion?

Can you cite another example that could demonstrate the differences in sound wave speed and light speed?

Most objects have a natural frequency of vibration. Sound Wave Interactions Natural Frequency Most objects have a natural frequency of vibration.

Sound Wave Interactions Natural Frequency For example, if a guitar string (fastened at its end on a guitar) is plucked, the waves created vibrate at the string’s natural frequency.

Sound Wave Interactions Natural Frequency If you change the length of the string, you will also change its natural frequency.

Sound Wave Interactions Resonance A phenomenon called resonance is very important in physics because is occurs in many mechanical and electrical systems.

Sound Wave Interactions Resonance Resonance is the transfer of energy from one system to another that vibrates at the same frequency (its natural frequency).

http://www.blazelabs.com/f-p-glass.asp http://www.regentsprep.org/Regents/physics/phys04/bresonan/default.htm http://id.mind.net/%7Ezona/mstm/physics/waves/interference/twoSource/TwoSourceInterference1.html http://www.colorado.edu/physics/2000/applets/fourier.html

Sound Wave Interactions Interference Interference is ability of two or more waves to combine and form a new wave.

Sound Wave Interactions Constructive interference occurs when the compressions of two or more waves arrive at the same place at the same time.

Sound Wave Interactions When this occurs, the compressions overlap and form a greater compression. As a result the sound will be louder.

Sound Wave Interactions Destructive interference occurs when the compressions of two waves do not arrive in the same place at the same time.

Sound Wave Interactions This will cause the amplitudes of the waves to rise and fall. A musician hears the variations of sound intensity as beats.

Sound Wave Interactions This will cause the amplitudes of the waves to rise and fall. A musician hears the variations of sound intensity as beats.

Applying Concepts How would musicians use interference to tune instruments?

Applying Concepts How would musicians use interference to tune instruments? Musicians adjust the instruments until the beats disappear. The beats disappear when the instruments produce waves of the same frequency and the instruments are “in tune”

Pop Tart Review What do you call the dense areas of a compressional wave?

Pop Tart Review What do you call the less dense areas of a compressional wave?

Pop Tart Review What causes sound waves?

Will sound travel better through air or glass? Pop Tart Review Will sound travel better through air or glass?

Pop Tart Review In addition to the type of medium, what affects the speed of sound

Pop Tart Review What is the difference between the crest of a wave and the trough of a wave?

Pop Tart Review Is sound a transverse wave or a compressional wave?