WAVES

Waves A wave is any disturbance that transmits ENERGY through matter and space. Waves carry energy NOT matter. SIM

Kinds of Waves –Longitudinal Wave The material that the wave is in vibrates back and forth along the path that the wave travels. SIM

Kinds of Waves –Transverse Wave The material that the wave is in moves perpendicular (at right angles) to the direction that the wave is traveling. SIM

Longitudinal Waves Compression –Section of a longitudinal wave where the particles are crowded together Rarefaction –Section of a longitudinal wave where the particles are less crowded than normal

SIM

Transverse Waves Crests –The highest point in a transverse wave. Troughs –The lowest point in a transverse wave. SIM

Crest and Trough

Amplitude –Maximum distance the wave vibrates from its rest position SIM

Which one of these waves has a larger amplitude?

Wavelength Wavelength (λ) –The distance from any point on one wave to that same point on the next wave SIM SIM2 λ λ

The wavelength of a longitudinal wave can be measured as the distance between the center of two compressions or rarefactions.

Which one of these waves has a larger wavelength ( λ) ?

Frequency –The number of waves (or cycles) produced in a given amount of time SIM

Which one of these waves has a higher frequency?

Review

Reflection –When a wave bounces back after striking a barrier SIM SIM2

Refraction –The bending of a wave as it passes at an angle from one material (medium) to another. SIM

Diffraction –The bending of waves around a barrier or through an opening. SIM SIM2

Interference Interference is the result of two or more waves overlapping. Constructive Interference –Occurs when the crests of one wave overlap the crests of another wave OR the troughs of the waves overlap

Interference Destructive Interference –Occurs when the crests of one wave and the troughs of another wave overlap

Interference SIM

Standing Waves Standing wave SIM SIM –A wave that forms a stationary pattern. –Portions of the wave do not move and other portions have a large amplitude –At rest= total destructive interference –Large amplitude=constructive interference.

Sound waves are reflected at a boundary. (SIM1) (SIM2)SIM

Sound waves are refracted at a boundary.

Interference. –Constructive interference –Destructive interference

Here’s what is occurring. (SIM1) (SIM2)SIM2 SIM - Interference

Multiple sound sources interfere (SIM)SIM Changing separation distance.

Multiple sound sources interfere. Changing source frequency.

What is a Medium? A substance through which a wave can travel –Water –People –Air –Coiled wire

What is a Mechanical Wave? A wave that requires a medium Examples: –Sound –Water

Resonance Objects have resonant frequencies An object vibrating at the resonant frequency of a second object causes the second object to vibrate too! SIM - Resonance

Speed of Sound Lightening/Thunder SIM

What Effects The Speed of Sound? Medium

What Effects The Speed of Sound? Temperature As the temperature rises, the sound travels faster! SIM

Pitch How high or low you perceive a sound to be Determined by the frequency High Pitch Low Pitch

Ultrasonic –Sounds with frequencies that are higher than 20,000 Hz Infrasonic- –Sounds with frequencies that are lower than 20 Hz

Volume Decibel (dB) - unit to express volume Exposure to sounds above 85 dB causes hearing loss SIM SIM - dB

What is an Ultrasound? Ultrasound Simulation

Beat Frequency Two waves with similar frequencies alternate constructive/destructive interference Causes sound to alternate loud and soft SIM

Beating Frequency (SIM1) (SIM2)SIMSIM2

Beating Frequency AppletBeating Frequency Applet 2 Beating Frequency Applet 3

Sound from: A stationary object A moving object (SIM1)SIM (SIM2)SIM2 SIM – Doppler Effect Labeled SIM – Hear Doppler SIM – Doppler/hear police siren SIM – Doppler/see police siren

Final Note: Mechanical waves and Electromagnetic Waves are different!

Sources: Bloomfield, How Things Work. Krauskopf & Beiser, The Physical Universe. 10 th ed. Tillery, Physical Science.