# 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