Physics Ch. 6

Front 1

Wave

Back 1

-transfer of momentum and energy from one point to another

3 types of waves:
-mechanical
-electromagnetic
-matter

Front 2

Mechanical waves

Back 2

-waves that require some medium through which to travel
-the medium, if perfectly elastic, is momentarily displaced by a wave and then returned to its original position

Front 3

Transverse wave

Back 3

-the medium is displaced perpendicularly to the direction of wave propagation

Front 4

Longitudinal wave

Back 4

-one in which the medium is displaced parallel to the direction of wave propagation, such as sound wave in air
-the phase-shifted sine function represents either the change in pressure or the horizontal displacement of the medium with respect to the time or displacement of the wave.

Front 5

Wavelength (A)

Back 5

-measured from any point in the wave to the point where the wave begins to repeat itself.

Front 6

Frequency

Back 6

-the number of wavelengths that pass a fixed point per second
-measured in hertz (Hz) or cycles per second.

Front 7

Equation for velocity of a wave

Back 7

v = (frequency)x(wavelength)

Front 8

Period

Back 8

T = 1/f
-the number of seconds required for one wavelength to pass a fixed point.

Front 9

Amplitude

Back 9

-the maximum displacement of a wave from zero.
-always positive.

Front 10

Effects of medium on velocity of a wave

Back 10

-the velocity of a wave is dictated by the medium through which the wave travels.
-velocity of a wave source does not effect the velocity of the wave itself

Front 11

2 aspects of the medium effect on wave velocity

Back 11

1. the medium's resistance to change in shape (or elasticity)
2. the medium's resistance to change in motion (or inertia)
-a heavier medium tends to slow waves down
-a stiffer medium tends to speed waves up
-for a gas, the velocity of a wave increases as temperature increases.

Front 12

Intensity

Back 12

-a measure of power, or rate of energy transfer
-used to measure wave intensity
-measured in W/m^2

Front 13

Intensity level (B) for sound

Back 13

-a logarithmic scale of intensities
-units are given in decibels (dB)

Front 14

Phase of a wave

Back 14

-relates wave frequency, wavelength, and place and time of origin.
-two wavelengths that are the same wavelength and begin at the same point are said to be in phase with each other.

Front 15

Constructive interference

Back 15

-occurs when the sum of the displacements results in greater displacement

Front 16

Destructive interference

Back 16

-occurs when the sum of displacements results in a smaller displacement.

Front 17

Beats

Back 17

-occur when two waves with slightly different frequency are superimposed.
-at some points they will be nearly in phase and experience constructive interference.
-at other points they will be out of phase destructive interference

Front 18

Beat frequency

Back 18

f(beat) = lf1-f2l

-beat points will alternate with a frequency equal to the difference between the frequencies of the two original waves.
-this difference is called beat frequency

Front 19

Node

Back 19

the point where two sine waves with the same wavelength traveling in opposite directions collide.
-A this point, there is NO displacement in the string, this is a node.

Front 20

Antinode

Back 20

-the points after and before a node which experience maximum constructive interference.

Front 21

Standing wave

Back 21

-when the string appears to hold perfectly still at the nodes and move violently up and down at the antinodes.

Front 22

Harmonic series

Back 22

-A list of wavelengths from largest to smallest of the possible standing waves for a given situation.
-Numbered from longest wavelength to shortest wavelength.

Front 23

First harmonic or Fundamental wavelength

Back 23

-the longest wavelength in the harmonic series
-created with the fewest number of nodes (2)

Front 24

Second harmonic

Back 24

-Made by adding another node to the harmonic

Front 25

Natural or resonant frequency

Back 25

-A standing wave causes an object to move at its natural or resonant frequency.

Front 26

Resonance

Back 26

-the condition where the natural frequency and the driving frequency are equal.

Front 27

Simple harmonic motion

Back 27

-motion exhibits a sinusoidal function
-can be described as an oscillation between kinetic and potential energy
-energy is conserved
example: mass on the end of a massless spring
example: pendulum

Front 28

Angular frequency of mass on a spring or pendulum

Back 28

w = (k/m)^(1/2) wack em -> mass on spring

w =(g/L)^(1/2) wiggle --> pendulum

-a way to remember that period does NOT depend on the mass in a pendulum.

Front 29

The Doppler Effect

Back 29

-results because waves are unaffected by the speed of the source which produces them.
-If the source moves relative to the receiver of the waves, each wave travels a different distance in order to reach the observer, therefore the observer will not receive them at the same frequency they were emitted.

Front 30

Equations to approximate the Doppler effect

Back 30

delta(f)/fs = v/c

f = frequency
v = relative velocity of source and the observer
c = wave velocity

delta(wavelength)/(wavelength)s = v/c

Remember: when relative velocity brings the source and observer closer, observed frequency goes up, wavelength goes down, so add f and subtract wavelength.