Vibrations and Waves

Question 1

Vibration

Answer 1

The repeated motion of a particle in a medium.

Question 2

Cycle

Answer 2

One complete vibration (oscillation)

Question 3

Wave

Answer 3

A disturbance that transfers energy over a distance

Question 4

What are the 3 types of vibrations?

Answer 4

Transverse Vibration, Longitudinal Vibration, Torsional Vibration

Question 5

Transverse Vibration

Answer 5

Object vibrates perpendicular to its axis. Ex: kid on swing, guitar string.

Question 6

Longitudinal Vibration

Answer 6

Object vibrates parallel to the axis. Ex: baby jumper, shocks on car.

Question 7

Torsional Vibration

Answer 7

Object twists back and forth around its axis.

Question 8

Amplitude

Answer 8

Distance from equilibrium position to max displacement

Question 9

Frequency

Answer 9

of cycles completed per unit time ( f = #cyc / total t )

Question 10

Period

Answer 10

The time to complete one full cycle. ( T = total t / #cyc )

Question 11

What is Periodic Motion?

Answer 11

Motion that occurs when the oscillation/vibration of an object repeats (exactly) in equal time intervals.

Question 12

What is the universal wave equation?

Answer 12

V=fλ

Question 13

What does a reflected pulse from a fixed end look like?

Answer 13

reflected and inverted

Question 14

What does a reflected pulse from a free end look like?

Answer 14

reflected

Question 15

What is the Principle of Superposition?

Answer 15

At any point on the medium the resulting amplitude is the algebraic sum of the two interfering amplitudes.

Question 16

Define Wave

Answer 16

A periodic disturbance which transfers energy over a distance

Question 17

What are the characteristics of a wave?

Answer 17

Crest: The region where the displacement is positive
Trough: The region where the displacement is negative
Amplitude (A): The distance above/below its equilibrium position to max displacement
Wavelength (λ): The distance between any consecutive points on the waves which are in phase (crest-crest)

Question 18

Does amplitude of a pulse affect its speed?

Answer 18

No

Question 19

Which is faster, the initial pulse or reflected pulse?

Answer 19

They should be equal.

Question 20

How do you make a wave go faster?

Answer 20

More force

Question 21

What happens to wavelength if frequency of vibrations is increased?

Answer 21

As frequency increases, wavelength decreases

Question 22

What is wave interference?

Answer 22

When two waves simultaneously act on the same particles in a given medium

Question 23

What are the two types of interference?

Answer 23

Destructive and Constructive interference

Question 24

Destructive Interference

Answer 24

The two amplitudes cause the waves to cancel out / reduce amplitude

Question 25

Constructive Interference

Answer 25

When two amplitudes build up creating a larger amplitude

Question 26

Node

Answer 26

Points at rest on a standing wave

Question 27

Anti node

Answer 27

Points between nodes which experience maximum displacement

Question 28

Why wont every frequency create a standing wave?

Answer 28

The λ and velocity must "fit" on the spring

Question 29

What happens when a wave moves to a slower medium?

Answer 29

If velocity decreases, λ decreases. The heavy/slow medium acts like a fixed end causing reflection to be inverted

Question 30

Resonant Frequency

Answer 30

The natural frequency at which an object vibrates best

Question 31

Mechanical Resonance

Answer 31

The transfer of energy from one object to another with the same natural frequency

Question 32

Sound Waves

Answer 32

A form of energy produced by a rapidly vibrating object. They are longitudinal vibrations which require a medium.

Question 33

Human Audible Range

Answer 33

20 Hz to 20 000 Hz

Question 34

Sound Intensity

Answer 34

Energy per unit area at a particular point per second measured in W/m^2

Question 35

Sound Intensity Level

Answer 35

Each increase by 10dB causes 10x as intense sound. Every 3dB increase doubles sound intensity.

Question 36

Hearing Loss/Protection

Answer 36

85dB = 8h max exposure. As the intensity doubles (safe) exposure time is cut in half.

Question 37

Resonance in closed air columns

Answer 37

1st resonant length = 1/4λ, 2nd r.l. = 3/4λ, 3rd r.l. = 5/4λ

Question 38

Resonance in open air columns

Answer 38

1st resonant length = 1/2λ, 2nd = 1λ, 3rd = 3/2λ

Question 39

Doppler effect

Answer 39

Moving towards = shorter λ, (Vw/Vw-Vs), fd > fs | Moving away = longer λ, (Vw/Vw+Vs), fd

Question 40

What are: (Vw), (Vs), (fs), (fd)

Answer 40

Vw: speed of wave, Vs: speed of source, fs: frequency of source, fd: observed (Doppler) frequency

Question 41

The Sound Barrier

Answer 41

As object velocity gets close to speed of sound, the highly compressed sound waves in front pile up and make it hard to break through

Question 42

Super-Sonic Speed

Answer 42

At speeds faster than the speed of sound, sound waves form a cone, trailing off behind (plane). Because the waves line up along the edges of the cone, we hear a sharp "crack" or sonic boom

Question 43

Mach Speed

Answer 43

Mach # = speed of object / speed of sound

Question 44

Beats

Answer 44

Two nearly identical sounds are played simultaneously and will both act constructively and destructively, producing alternating loud and quiet sound waves (beats).

Question 45

Beat frequency

Answer 45

f(beat) = I f2-f1 I