2.5 Wave Motion and Sound

Question 1

What is a mechanical wave?

Answer 1

An oscillation of matter, that requires a medium through which to transmit energy.

Question 2

What are some examples of mechanical waves?

Answer 2

Sound, slinkys and water.

Question 3

What distinguishes a mechanical wave from an electro magnetic wave?

Answer 3

Mechanical waves cannot exist in a vacuum.

Question 4

How can mechanical waves be classified?

Answer 4

Transverse or longitudinal.

Question 5

What is a transverse wave?

Answer 5

Causes the medium to vibrate perpendicular to the direction of travel. The highest point is the crest and the lowest is the trough.

Question 6

How are water waves transverse?

Answer 6

The molecules move up and down in the water whilst the waves move left to right.

Question 7

What is a longitudinal wave?

Answer 7

The displacement is parallel to the movement of the wave.

Question 8

What are the two types of movement in a longitudinal wave?

Answer 8

When they are close together it is compression and when they are spread out it is rarefaction.

Question 9

What is a sine wave?

Answer 9

A waveform that repeats itself in fixed form.

Question 10

What is amplitude?

Answer 10

The highest point of displacement from the rest point. (How high the peak goes from the centre line).

Question 11

What is wavelength?

Answer 11

The space between each peak.

Question 12

What is periodic time?

Answer 12

The time taken to complete one oscillation.

Question 13

What is the frequency?

Answer 13

The number of oscillations in one second.

Question 14

What is the formula for wavelength?

Answer 14

Wave speed (v) divided by frequency (f)

Question 15

What is wave interference?

Answer 15

When two waves meet on the same medium and form a resultant wave that can be greater, lower or the same amplitude.

Question 16

What is a standing wave?

Answer 16

Where two waves meet and the oscillation causes a mixed result. Sometimes the oscillation will be maximised and other times it will be net zero.

Question 17

What is the speed of sound ?

Answer 17

Air-343m/s
Water- 1500m/s
Steel- 5000m/s

Question 18

Why is the speed of sound in air important?

Answer 18

For aerodynamics, it is the point at which the air is increasingly compressible and flying characteristics change dramatically.

Question 19

What does the speed of sound depend on?

Answer 19

The ambient temperature.

Question 20

What is the equation for the speed of sound?

Answer 20

20 x √T

Question 21

What is the mach number?

Answer 21

The speed of the aircraft in relation to the speed of sound.

Question 22

What is propagation of sound?

Answer 22

Production of sound through an elastic medium such as air.

Question 23

How is the intensity or amplitude of a sound specified?

Answer 23

Pressure- decibels or SPL (sound pressure level)

Question 24

What decibel level if exposed too for a prolonged time can cause damage?

Answer 24

85db

Question 25

What is maximum level an human ear can withstand?

Answer 25

130db

Question 26

What is the doppler effect?

Answer 26

The change in frequency of a wave caused by the movement of a body relative to the wave source.

Question 27

What is a good example of doppler effect?

Answer 27

An ambulance driving past with the sirens on.

Question 28

Where is the doppler effect used in aircraft?

Answer 28

Weather radars to detect turbulent weather by measuring the motion of rain droplets in addition to the intensity of precipitation.