Transcript Waves and Sound - Lancaster City School District

Waves and Sound
Objectives
• By the end of today, you will be able to:
• Define and describe basic properties of a
wave
• Relate the pitch of a sound to its
frequency
• Describe what happens to air when sound
moves through it.
• PS - G-19,20
• SI - A-3
Vibrations and Waves
• What is a wave?
• A wave can be described as a disturbance
that transfers energy through matter or
space.
• This disturbance can be thought of as a
vibration
• EX: Slinky
Vibrations and Waves
• This vibration, or disturbance, can be a vibration
of matter or it can be a vibration of pure energy.
• Sound is the vibrations of matter - through
solids, liquids, and gases
• Light is a vibration of electric and magnetic
fields - a vibration of pure energy.
• Waves carry energy!
Wave Properties
•
The high point in a wave is called the crest.
•
The low point in a wave is called the trough.
•
The amplitude of a wave is the distance from the
midpoint to the crest or trough
•
The wavelength of a wave is the distance from one
crest/trough to the next crest/trough
Wave Properties
•
Frequency is the number of vibrations in a specific
amount of time (usually 1 sec.)
•
In other words, the number of wave cycles that
pass a point in a given time
•
Usually the number of crests that pass a
point in a given time.
Wave Properties
•
The unit of frequency is the hertz (Hz).
•
1 Hz = 1 vibration per second
•
Ex. - Radio Waves
•
AM radio waves are measured in kHz
•
•
1320 AM broadcasts radio waves at a
frequency of 1,320,000 vibrations per second.
FM radio waves are measured in MHz
•
96.3 FM broadcasts at a frequency of
96,300,000 vibrations per second.
Wave Properties
•
The period of a wave is the time it takes for one cycle/vibration
to be completed.
•
Frequency and Period are related.
•
Ex. - A wave that has a frequency of 2 Hz
•
This means that there are 2 cycles in 1 second.
•
Therefore, the period of the wave is going to be 1/2
second.
•
One cycle, or period, is completed in 1/2 seconds.
Wave Properties
•
Two types of waves: transverse and longitudinal
•
Transverse - waves travel at right angles (perpendicular) to the
direction of the wave source.
•
•
Shaking a blanket when you’re making your bed
Longitudinal - waves travel along (parallel) to the direction in of
the wave source.
•
Pushing or pulling a Slinky very fast. Part of the slinky is
pushed together(compression) and other parts are
stretched (rarefactions).
Sound Waves
•
Sound waves occur when vibrations travel through
matter. It has to have a medium.
•
In the air, sound waves are produced when the air
molecules are vibrated.
•
The air goes through compressions and
rarefactions, and sound is produced.
•
Like in a tuning fork:
Sound Waves
• Solids, liquids, and gases can transmit
sound.
• Many solids and liquids conduct sound
better than air.
• Think of putting your ear against the
wall to hear what is going on in the next
room, or think of what you can hear
when you are swimming under water!
Sound Waves
• The highness or lowness of a sound is
called pitch.
• A high pitch sound has a high frequency
• A low pitch sound has a low frequency
• The human ear can hear pitches that
range from about 20 - 20,000 Hz.
• Mosquito Ringtone
Activity
• Wave Diagram - Draw and Label a wave
diagram (like Fig. 13.1 on pg 211). Label the
amplitude, wavelength, crest, and trough.
• You can complete this on the bottom
of your notes.