Transcript Source of waves

Source of waves
•All types of waves are formed from something
vibrating
•An object that vibrates in a very regular way is
said to be in “simple harmonic motion”
• These simple harmonic motions are part of
nature and are described in math by sine waves
Waves do one thing
• Waves transfer energy without transferring
the matter of the media
• Even ocean waves in the open sea don’t move
any water (for the most part) they only move
up and down.
General Wave Notes and Flavors
Media/medium-the matter which a wave passes
through.
What does a psychic medium do?
Mechanical Wave - a wave that needs a medium
to travel through (flavor 1)
Electromagnetic Wave– a wave that does not
need a medium to travel through (flavor 2)
We will talk about electromagnetic waves….. a
lot…………..but not now.
Mechanical waves come in 2 flavors
• Transverse- a mechanical wave where the
mediums displacement is perpendicular to the
movement (propagation) of the wave
• Longitudinal (compression)- a mechanical
wave where the displacement of the medium
is parallel the movement (propagation) of the
wave
– Compression—positive amplitude
– Rarefaction– negative amplitude
Mechanical waves come in 2 flavors
• Transverse- applet
• Longitudinal (compression)- applet
Wave Parts
• Transverse and Longitudinal waves have the
same parts, but they are easier to see in a
transverse wave.
• Wavelength – distance between identical
parts on two adjacent wave forms
Wave Parts
• Amplitude- Displacement from the
undisturbed location at a given point in a wave
form. There is a positive and negative
Wave Parts
• Crest – Maximum positive amplitude of a wave
form
• Trough– Minimum negative amplitude of a
wave form.
Pulses
• A pulse is ½ of an full wave.
• It can be positive or negative
• What does positive or negative mean for a
longitudinal wave?
• A full wave cycle is called an oscillation
Wave Measurements
• Amplitude of a wave– measured in many
different ways, from pressure to meters, don’t
worry too much about this, we won’t be using it
to do any math.
• Cycle or Oscillation- one complete motion of a
wave.
• Wavelength (λ)—is measured in a unit of
length, for us that will be meters (m)
Wave Measurements
• Frequency (f) —is the number of times an
identical part of a series of waves passes a given
point during a unit of time. Usually measured
in cycles per second.
– 1 cycle/second = 1 Hertz (Hz)
• Period (T) – the period of a wave is the time it
takes to complete one oscillation, measured in
time, for us it is usually seconds (s)
• f = 1/T
Speed of Waves
• In the slinky lab, where you able to make a
wave travel faster in the slinky?
• The speed of a wave is determined by
“characteristics” of the medium
• Transverse wave applet
• The speed of waves can be related to
frequency and wavelength as follows:
ν=λf
Let’s use v=fλ
• NOAA (National Oceanic and Atmospheric
administration) uses buoys to monitor ocean
activity. If the distance between two buoys is
100m and there are 15 crests, what is the λ?
• If the buoy is bobbing up and down 12 times
every minute, what is the frequency of the
waves in Hz?
• How fast are the waves moving?
• What is the period of a wave?
• λ=6.66m
f= 0.2Hz v= 1.33m/s T = 5s
Reflections
• I regret not going to my dad’s 50th birthday party
• I wish I had studied abroad
• When waves propagate into a new material it is
called the intersection is called a boundary
• When waves meet an immovable surface the
waves tend to bounce off or reflect.
• There are two types of boundaries
– A free boundary- the wave reflects with the same
amplitude
– A fixed boundary- The wave reflects with the
opposite amplitude
Interference
• 2 or more waves traveling in the same
medium can interfere with each other, this
takes two forms
• Constructive interference – when two waves
meet at a point and the amplitude of the
combined wave increases.
• Destructive interference – when two waves
meet at a point and the amplitude of the
combined wave decreases.
Standing waves
• A standing wave or stationary wave results
from the constructive/destructive interference
of a wave which reflects back through a
medium.
This is often the case in nature, such as a string
on a guitar.
Diffraction
• Waves have a tendency to bend around the
edge of an object.
• They do this when the hit an obstacle, an
opening, or an edge
• This phenomena is called diffraction
Diffraction
• Ripple tank applet
Real Waves
• Big Wave Surfing