Ch. 13.1-13.4 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

13.1 Vibrations and Waves

• What is a wave?

• A wave can be described as a disturbance that travels through a medium from one location to another location.

• This disturbance can be thought of as a vibration

• A medium is a substance or material that carries the wave.

13.1 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!

13.1 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

13.1 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.

13.1 Wave Properties• The unit of frequency is the hertz (Hz).

• 1 Hz = 1 vibration (cycle) 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.

13.1 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.

13.1 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.

• Ultrasonic Ringtones

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.

HW to be started. . . .now!

• Pg 231 - RQ’s 1,2, and 5-7