Summary

Unit One

                    Oscillatory motion

Vibrational motion:

* The motion done by the vibrating body at both sides of its rest point (original position) where it repeats itself at equal time intervals.

* Application of vibrational motion the micro-wave to cook the food.

Amplitude:

* The maximum displacement reached by the vibrating body far from its original position.

The complete Oscillation (cycle):

The motion done by the vibrating body when it passes at a certain point in its path two successive times in the same direction.

Note:

The complete vibration contain four amplitudes.

The Periodic time:

* The time taken by the vibrating body to make a complete vibration.

Frequency:

The number of complete vibrations done by the vibrating body in one second.

Frequency is measured by unit called Hertz (HZ) or multiplications of Hertz.

1- Kilo Hertz = 1000 Hertz or (10³) HZ

2- Mega Hertz = 1000,000 HZ or (10⁶) HZ

3- Giga Hertz = 1000,000,000 HZ or (10⁹) HZ

                    The wave motion

The wave:

A disturbance in medium that propagates in certain direction and transfers energy in its propagation direction.

The wave motion:

* The total movement of particles of medium at certain moment and in certain direction.

The wave propagation direction:

The direction in which the wave propagates.

Types of waves: 1- Electromagnetic waves

2- Mechanical waves

Transverse waves	Longitudinal waves
-         The particles vibrate in perpendicular direction to the wave propagation direction. -         They consist of crests and troughs.	-         The particles vibrate along the wave propagation direction. -         They consist of compressions and rarefactions.

 

Crest:

The maximum displacements upwards.

Trough:

The maximum displacement downwards.

Compression:

The place in which the density and pressure of longitudinal wave increases.

Rarefaction:

The place in which the density and pressure of longitudinal wave decreases.

Life application of waves:

Massage pools (Gakozy)

Mechanical waves:

- Waves that need a medium to propagate like water waves – sound waves.

- They propagate in different media with different velocities.

- They can’t propagate in space.

Electromagnetic waves:- Waves don’t need a medium to propagate and they can propagate in space

Ex: Light waves – Radio waves- All of them are transverse waves spread by speed 3 × 10⁸ m / sec

Concepts related to waves motion:

1- The wave length ()

- The distance between the centres of two successive crests or troughs in transverse waves.

- Or the distance between the centres of two successive compressions or rarefactions

- Wave length is measured by metre or parts of metre.

2- Amplitude:

The maximum displacement reached by particles far from their rest point (original position)

3- (Wave Velocity):

The distance travelled by wave in one second.

Note:

- Wave velocity is constant in the same medium and different in different media.

- The law of wave propagation

Velocity = Frequency × Wave length

     V       =                  ×         

                    Properties of sound waves

        Sound is an external effect affects on ear causing sense of hearing.

        Sound is produced due to vibration of bodies, and it stops when vibration stops.

        Sound is mechanical longitudinal waves, propagate in medium as spherical waves and its centre is the source of sound.

        Sound velocity in air is 340 m/sec and it increases or decreases in different media.

Properties of sound are:

1) Sound pitch

2) Sound intensity

3) Sound quality

1- Sound pitch:

  The property by which human ear can distinguish between sharp and rough sounds.

  Sound pitch depends on frequency:

-         High frequency :- sharp

-         Low frequency :- rough

2- Sound intensity:

  The property by which the human ear can distinguish between strong and weak sounds.

Sound intensity is measured by unit Watt/m²

Intensity of noise is measured by unit Decibel.

  Factors that affect sound intensity:

a- Distance between sound source and ear

b- Amplitude of sound

c- Surface area of vibration

d- Density of medium

e- Wind direction

  Application on sound intensity:

Ears blocks that are made of silicon to protect ears from noise.

3- Sound quality

  The property by which human ear can distinguish between sounds from different sources even they have the same pitch and intensity.

  We can distinguish between sounds due to presence of harmonic waves that accompany the fundamental waves produced.

  Audible and non-audible waves.

  Audible waves (sonic waves) have frequency ranges between 20:20.000 Hz.

  Non-audible waves:

-         Infrasonic waves’ frequency less than 20 Hz.

-         Ultrasonic waves’ frequency more than 20.000 Hz.

Uses of ultrasonic waves:

1) Decaying of stones in kidney and ureters.

2) Diagnosis of some diseases and treatment of cancer.

3) Sterilizing of food.

4) Detection of explosives underground (Landmines).

                    Reflection of sound

Sound reflection:

The rebounding of sound waves when they fall on a reflecting surface.

Laws of sound reflection:

1) Angle of incidence = angle of reflection

2) The incident sound ray, reflected sound ray, and the perpendicular line from point of incidence on reflecting surface are all in one plane perpendicular to the reflecting surface.

Echo:

The repetition of sound due to reflection.

Conditions of echo:

1) Huge reflecting surface.

2) Time not less than 0.1 second.

3) Distance not less than 17 metres.

Applications on echo:

1) Determine sound velocity in air

2) Concentration of sound by using concave surfaces.

3) Estimation of sea depth and places of fish gathering.

4) Examining weldings of metals in industry.

5) Medical examinations.

6) Used by bats to fly in darkness.

                    Nature of light waves