Vocab
Mechanical Waves, Transverse Waves, Longitudinal Waves, Standing Waves, Pressure Waves
- Mechanical: A wave that needs a medium (like air, water, or a solid) to travel through
- Transverse: Particles vibrate in a perpendicular direction (up and down)
- Longitudinal: Particles vibrate in a parallel direction like a sound wave (back and forth)
- Standing: A wave pattern that stays in one place and does not travel
- Pressure: Particles bunch up and spread out as it moves, like sound traveling through air
Nodes v Antinodes
Nodes: Points that don’t move (no displacement)
Antinodes: Points that move the most (maximum displacement)
Pendulums
- Consists of a heavy object (bob) suspended by a string
- Once in motion it exhibits simple harmonic motion
- T = 2pi√(l/g)
- (L = length of string) and (g = acceleration due to gravity)
What if the source is moving faster than sound?
- The source outruns its sound waves
- The waves pile up in front of it, forming a shock wave
- We hear this as a sonic boom
Wave Pulses
A single disturbance that moves through a medium
Periodic Motion
Motion that repeats regularly over a given time interval
High Frequencies V Low Frequencies
- High: Vibrations are close together
- Low: Vibrations are far apart
Examples of Wave Interference
Constructive: 2 speakers playing the same music next to each other
Destructive: Noise cancelling headphones
Period T [s], Frequency f [Hz], Amplitude A [m], Wavelength λ [m]
Period: Time for one complete wave cycle to pass a point
Frequency: The number of cycles that pass a point per second
Amplitude: how tall the wave is (greater amplitude = more energy the wave carries)
Wavelength: The distance between two nearest points on a wave
Restoring Force
A force that brings an object back to its rest position
Example: Gravity bringing a moving swing back to its center
Why can nobody hear you scream in space?
- Sound waves are waves of a compressed medium
- No medium means no sound
Wave Interference
When two or more waves meet and overlap, creating a new wave pattern (constructive or destructive)
Wave Speed
How fast a wave travels through a medium (v=fλ)
Harmonic Motion
At Equilibrium: Maximum speed, zero displacement, zero acceleration
At Maximum Displacement: Zero velocity, acceleration is maximum but in opposite direction as displacement
Speed of Sound
- Dependent on the medium it is traveling in
- The speed of sound in air of temperature 200C is 343 m/s
- The speed increases 0.60 m/s with each 10C increase in temperature
What can happen when a wave hits a boundary?
The energy reflects backward
Reflection: The wave bounces back
Refraction: The wave changes direction
Transmission: The wave passes into the new medium
Absorption: The wave loses energy to the boundary
Destructive Interference V Constructive Interference
Constructive: When crest meets crest OR trough meets trough
Destructive: When crest meets trough OR trough meets crest
Period of a Spring System
- Larger mass increases period -> more inertia to drag back and forth
- Larger spring constant decreases period -> more force to pull quicker
- Ts = 2pi√(m/k)
- (k = spring constant)
Doppler Effect
- Source of sound is closet to you: Pitch is higher
- Source of sound is far from you: Pitch is lower
- fd = fs (v - vd/v - vs)
- fs is original frequency, fd is new heard frequency, v is the speed of the wave, vd is the speed of the thing hearing, vs is the speed of the source of the sound
Parts of a Spring
Compression: Compressed part of the spring
Rarefaction: Wider part of the spring