All matter is made of _______________Particles are constantly ______________As temperature increases, particles move
__________As temperature increases, distance between
particles _______________What state of matter does each of these images
represent?
Recall: The Particle Theory of Matter
VibrationImagine a pendulum:
Point #2 represents the equilibrium position.
Points #1 and #3 are equal distancesaway from equilibrium.
vibration: the cyclical motion of an object about an equilibrium point (one back and forth motion of the pendulum)
What’s happening to the energy of the bob as it goes through each vibration(i.e. goes through a cycle)?
What if you were looking at the motion of particles instead?
Mechanical WaveTransfer of energy through a material due
to vibrationThe material is called a medium
Can be solid, liquid, or gas
How long a vibration can continue in a medium depends on how much energy is gained/lost by the medium in the vibration. (usually very little)
Net MotionThe displacement of a particle over a
certain time interval. The difference between the particle’s initial and final positions
Net motion of particles causes the vibrationIdeally, net motion is zero once vibration has
stopped. Therefore no work is done and no energy is lost by the vibration
Particle Behaviour in Different MediaAll vibrations need a medium to transfer the waves.
A medium’s effectiveness at transmitting vibrations depends on its molecular and mechanical structure density temperature
Speed and distance a wave can travel depends on the composition of the medium. more rigid = faster waves that travel fartherless rigid = disperse more energy thus reducing speed and distance
Particle Behaviour in Different Media
SolidsAtoms held together in crystal formation so
they can only vibrate slightlyElastic: medium returns to its original shape
after being disturbedMost solids have this property
Rigid materials transfer energy more efficiently than non-rigid materials
Particle Behaviour in Different MediaFluidsLiquid molecules are in contact, so they are
still very effective transmitters of wavesGases have the lowest particle density, so
they are the least effective wave transmittersGases rely on translational motion:
The straight-line motion of a molecule
Types of Mechanical WavesTransverse Waves: particles vibrate
perpendicular to the direction of energy flow. Eg. Guitar string: energy flows down the string
but motion is back and forth from the finger/pick plucking the string
Longitudinal Wave: particles vibrate parallel to the direction of energy flow.Eg. slinky
Parts of a Longitudinal WaveCompressions: regions where particles in a
wave are close together (high pressure in gasses)
Rarefactions: regions where particles in a wave are further apart (low pressure in gasses)
SoundLongitudinal waves produce sound:
Energy produced by rapidly vibrating objects that are detectable by the ear
Sound (and other forms of energy, too) is transmitted ONLY as a longitudinal wave in fluids, but can be either transverse or longitudinal in solids.
What Type of Wave?A complex wave – combination of both types due to wind effects near the surface
Wave CharacteristicsTime-based characteristics:
CycleOne complete vibration = one cycle
Frequency (f)Number of cycles per secondUnits: 1/s = hertz (Hz)
Period (T)Time required for one cycle
f = 1/T and T = 1/f
Wave CharacteristicsAmplitude• Maximum distance from equilibrium
Wavelength (λ)Distance between midpoints of two crests, or midpoints of two troughs
Wave CharacteristicsPhaseThe x-coordinate of a particleWhen the waveform has been shifted along
the x-axis, this is a phase shiftParticles are considered to be in phase
when:They have the same amplitudeThey are vibrating in the same directionThey have the same phase shift
SHOW WAVE INTERACTION IN MY NELSON
HomeworkFrom textbook:
8.1 Practice Questions #1 - 5
8.2 Practice Questions # 1-6, 8
8.3 Practice Questions # 1, 4, 5