Periodic Motion Common Example: Pendulum Some elements of periodic motion we can describe –Oscillation or Cycle –Period, T –Frequency, f –Amplitude, A Another Common Example: Mass on a spring

Waves One cycle Another cycle

Waves Wavelength Wavelength Crest Trough Distance traveled by the wave in 1 cycle is the wavelength, Amplitude A Amplitude A Frequency, f : number of cycles that the wave goes through in a unit time (usually 1 s)

Waves/Periodic Motion You are sitting on a dock, and using binoculars, you notice a boat bobbing in the distance. You notice that if you start timing when the boat has bobbed up, at the end of 2 seconds, the boat has bobbed up 6 more times. You also notice that the distance between the wave crests causing the boat to bob up (and down) is 4 m. a. What is the frequency of the waves? b. What is the wavelength? c. What is the period? d. What is the speed of these waves?

Classification of Waves Transverse Wave Longitudinal Wave Direction of oscillation is ⊥ to direction of propagation Direction of oscillation is along direction of propagation

Sound Waves Compression and Rarefactions

Frequency and Sound Waves Frequency of Sound is perceived as pitch Most humans can detect sound with frequency ranging from 20 to 20,000 Hz Below 20 Hz is called infrasonic Above Hz is called ultrasonic the mosquito

Speed of Sound Waves at 20 o C in air is about 340 m/s

Some Important Properties of Waves Reflection Doppler Effect Refraction Interference

Echo Location At a particular temperature, sound travels in water at about 1530 m/s in water. If a dolphin emits a sonar cry and hears the echo 3s later, how far away from the dolphin is the object from which the signal is reflected?