AP Physics Review Waves and Sound

Wave Parts Wavelength can be the distance between the same point on any two corresponding waves Frequency is the number of waves per second (units are HZ) Period is the number of seconds per wave (units are s) One wave is one complete crest and one complete trough. Amplitude is the height of the wave and is related to the energy of the wave. in sound, that would be the volume

Pulses and Boundaries A pulse is a disturbance that creates a wave. Waves transfer energy only. A pulse moves through the medium (substance). The speed of the pulse depends on the medium. A boundary can be rigid, loose, or a change in the medium. They waves behaves differently with different boundaries.

Superposition When two waves are traveling in opposite directions in the same medium at the same time, they will interfere. The amplitudes of the waves are added together. If the initial waves are on the same side of the medium, the resulting amplitude will be larger and therefore constructively interfere. If the initial waves are on opposite sides of the medium, the resulting amplitude decreasing making it destructive interference. After the interaction, the waves continue on with their original properties as if nothing happened.

Types of Waves Transverse Wave – The motion of the energy is perpendicular to the motion of the medium. Ex. Water waves, light waves Longitudinal Wave – The motion of the energy is parallel to the motion of the medium. Ex. Sound waves.

Standing Waves and Resonance Form when a wave reflects off of a boundary and interferes with waves traveling in the opposite direction. They form nodes (destructive interference) and antinodes(constructive interference) These can build up to and reinforce each other to create resonance. Resonance can cause another object to vibrate based on the objects natural frequency. Fundamental mode is one antinode and two nodes. ½ λ

Wave Behavior Refraction – changing direction and speed when entering a new medium Diffraction – a wave bending around a barrier or bending as it goes through an opening in the barrier. The amount of diffraction is dependent upon the size of the opening and the wavelength of the wave.

Sound Longitudinal mechanical wave that is a series of compressions and rarefactions in the air. The more dense the medium the faster sound travels but contradictory to that, as the temperature of air increases, so does the speed of sound. Acoustic range – frequencies humans can hear Infrasonic range – frequencies below the acoustic range. Ultrasonic range – frequencies above the acoustic range. The amplitude of a sound (intensity of the pressure in the compression) determines the loudness. Frequency determines the pitch.

Doppler Effect The apparent change in the frequency heard when the observer or the source is moving. When the moving closer together, the frequency appears higher and the wavelength decreases. When moving away from each other, the frequency appears to decrease and the wavelength increases. The frequency of the sound emitted from the source doesn’t really change but it appears to change based on the motion.