Periodic Motion and Waves

17A Periodic Motion

• Periodic Motion: motion that repeats in equal time intervals

• Period: the time interval (T) for one complete cycle of the periodic motion

• Periodic Motion of a Spring System

1. Compressing the Spring

2. The Expanding Spring

3. Momentum Stretches the Spring

4. Spring Compresses Again

5. The Recoiling Spring

• Using Periodic Motion

  • Damping: reducing the amplitude of periodic motion by applying a force that works against the motion

  • Damped Oscillator: a system that is designed to oscillate but includes a force to reduce the amplitude

  • Driven Oscillator: a system that is designed to oscillate at a constant amplitude by including a force to overcome frictional losses

  • Resonance: an increase in the amplitude of a vibration due to additional wave input

17B Waves

• Defining Waves

  • Wave: a disruption that carries energy from one location to another

  • Mechanical Wave: a wave that carries energy through a physical medium

  • Electromagnet Wave: a disruption in an electromagnetic field that carries energy, even through the vacuum of space

• Describing Waves

  • Crest: the highest point of a wave

  • Trough: the lowest point of a wave

  • Wavelength: the distance between two identical points on successive waves

  • Wave Height: the vertical distance between the trough and crest of a wave

  • Amplitude: the maximum displacement from the equilibrium position during periodic motion

• Classifying Waves

  • Transverse Wave: a wave in which the disruptions move perpendicular to the direction of wave travel

  • Longitudinal Wave: a wave in which the disruptions are parallel to the direction of wave travel

  • Compression: a region of high density and pressure in a longitudinal (compression) wave

  • Rarefaction: a region of lower density and pressure in a longitudinal (compression) wave

  • Surface Wave: a wave that occurs along the interface between two media

• Measuring Waves

  • Frequency: the number of waves or cycles that occurs per second

17C Wave Behavior

• Behavior of Waves

  • Reflection: the bouncing of waves off a surface

    • Regular Reflection: reflection that occurs when a smooth surface reflects light rays in mostly the same direction; also known as specular reflection. A perfectly regular reflection is mirror-like, reflecting all rays and wavelengths uniformly

    • Diffuse Reflection: the reflection off a rough or uneven surface that reflects light rays in all directions

  • Refraction: a change in wave direction due to a change in a wave’s speed as it enters a new medium

• Standing Wave: a wave that is moving even though the locations of the crests and troughs appear to be stationary

• Doppler Effect: the perceived change in the frequency of a wave due to the motion of the wave’s source or of the receiver