AP Physics B IV.A Wave Motion. Two features common to all waves mechanical waves A wave is a traveling disturbance A wave carries energy from place to.

AP Physics B IV.A

Wave Motion

Two features common to all waves mechanical waves

• A wave is a traveling disturbance

• A wave carries energy from place to place without transferring matter

Two types of waves

• Transverse – the disturbance is perpendicular to the direction of the motion

• Longitudinal – the disturbance is parallel to the direction of the motion

Wave terminology

• Equilibrium position

• Crest and trough

• Wavelength

• Amplitude

• Period

• Frequency

Speed of a wavev = fλ

Importante – the frequency of the wave is determined by the source.

The speed of the wave is determined by the medium.

Ex. A traveling wave on a rope has a frequency of 2.5 Hz. If the speed of the wave is 1.5 m/s, what are its period and wavelength?

Ex. The period of a traveling wave is 0.5 s, its amplitude is 10.0 cm and its wavelength is 0.4 m. What is the frequency and speed of the wave? What is the total vertical distance the wave travels in 2.0 s?

Superposition of waves

Reflections of a wave at a fixed and free end.

Standing waves – demo

Harmonics for a sting fixed between two points

Ex. A string of length 1.2 m that is fixed at both ends supports a standing wave with a total of 5 nodes and 4 antinodes. What is the wavelength of the standing wave? What is the harmonic? What is the frequency of the wave if its speed is 4.0 m/s?

Ex. A string fixed at both ends has four nodes and three antinodes. Each antinode has a length of 0.5 m. What is the wavelength of the wave and length of the string?

Ex. What are the first three harmonics of a string fixed at both ends if the speed of the wave is 120 m/s and the length of the string is 0.4 m?

Sound Waves

Sound is a longitudinal wave created by a vibrating object.

Terminology for sound waves

• Compressions

• Rarefactions

• Wavelength

Ex. A sound wave with a frequency of 300 Hz travels through air. A) What is its wavelength if the speed of sound in air is 340 m/s? B) If the frequency of the wave in increased to 600 Hz, what is its speed and wavelength?

Ex. A sound wave traveling through water has a frequency of 500 Hz and a wavelength of 3 m. How fast does the sound travel through water?

Forced Vibrations and Resonance

Examples of Resonance

• Swings

• Trampolines

• Breaking the goblet

• Tacoma Narrows Bridge

• KC Hotel walkway

Resonance for sound waves in open and closed pipes

The harmonics of an open pipe.

The harmonics of a closed pipe

Ex. A closed end tube resonantes at a fundmental frequency of 440.0 Hz. The air in the tube is at a temperature of 20.0º C and it conducts sound at a speed of 343 m/s. a) What is the length of the tube? B) What are the frequencies of the next two harmonics? C) Answer questions A and B above for a tube that is open at both ends.

Beat frequency

Ex. A piano tuner uses a tuning fork to adjust the key that plays “concert A”, (f = 400 Hz). When the tuning fork and he piano key are struck, three beats are heard. What is the frequency of the piano key?

The Doppler Effect and an irritating little demo