Science 2nd prep. 2nd term unit 1 lesson 2 part 1
** you know that motion is an example of periodic motion.
** if you throw a stone in water, concentric circles propagate
on the water surface.
This motion represents wave motion.
Activity >>> defining the concept of wave and its role
in energy transfer:
Procedures:
1 – arrange the dominoes' pieces in a row at equal
distances.
2- push the first piece.
Observation:
The pieces fall one after the other, and don't change their
positions.
Explanation:
1 – when the first domino piece falls, it will transfer its
energy to the second piece which falls transferring its energy to
the third and so on.
2 – transfer of energy continues.
Conclusion:
The disturbance that propagates and transfers energy in the
direction of propagation is known as the wave.
The wave:
It is the disturbance that propagates and transfers energy in
the direction of propagation.
Exercise:
How do you explain the motion of the coin Y when the coin X is
pushed though they never touch?!!
· the energy of the first coin X is transferred to the second
coin which transfers the energy to the third and to the fourth
until it reaches the last coin Y.
· the last coin gains energy and does not find another coin to
give it this energy, so that it moves away.
Activity >>> concluding the concept of wave motion:
Materials:
· a hollow glass tube 30 cm long.
· A candle
· A burning incense stick.
· A tuning fork.
Procedures:
1 – fix horizontally the glass tube.
2 – put the burning candle at one end of the tube.
3 – tab the tuning fork and let it vibrate at the other end of
the tube near burning incense stick.
Observation:
1 – the flame of candle vibrates.
2 – sound waves have transferred energy from vibrating tuning
fork to the candle flame.
3 – vapour of burning incense stick does not enter the tube
which indicates the air molecules do not move with the sound waves
through the tube.
Explanation:
1 – energy is generated when he tuning fork vibrates. This
energy is transferred in the form of sound waves.
2 – the medium particles ( air and smoke particles ) do not move
from their places during the propagation of sound waves which carry
energy to the candle flame.
Conclusion:
The movement resulting from the vibration of the medium
particles at a certain moment in a specific direction is known as
wave motion.
Wave motion:
It is the motion produced as a result of the vibration of the
medium particles at a certain moment and in a definite
direction.
The line of wave propagation:
It is the direction through which the wave propagates.
>>> According to direction of vibration of medium
particles relative to the direction of propagation:
>>> according to the ability to propagate and transfer
energy into:
*** why we can't hear the solar explosions occurring on the sun?
But we can see the light coming out of it?
*** why we hear the thunder after seeing lightning, although
they happen at the same time?
Sound of solar explosions and thunder is a type of mechanical
waves, while the sun light is electromagnetic waves which propagate
through vacuum with great velocity (3 × 108 m/s )
Comparison between mechanical and electromagnetic waves:
Mechanical waves
Electromagnetic waves
They need a medium to propagate.
They don't need medium to propagate.
They don't propagate through vacuum
They propagate through vacuum ( space ).
They are transverse waves or longitudinal waves.
They are all transverse waves.
Their speed is relatively low.
Their speed is great. (3 × 108 m/s )
Examples :
· water waves (transverse waves)
· sound waves (longitudinal waves)
Examples;
· light waves.
· Radio waves. ( used in radars.)
water waves and sound waves are mechanical waves?
Because hey need a medium to propagate through.
Light waves and radio waves are electromagnetic waves?
Because they don't need a medium to propagate through.
Enrchment information:
** electromagnetic waves are a type of transverse waves that can
propagate in free space.
** they consists of electric field and a magnetic field
perpendicular to each other and to the direction of wave
propagation.
Activity >>> to show the nature of transverse
waves:
Materials and tools:
· spring
· colored tape.
· Nail.
Procedures:
1 – fix one end of the spring to a wall using the nail.
2 – tie the coloured tape in the middle of the spring.
3 – move the free end of the spring up and down perpendicular to
the axis of the spring.
Observation:
1 – the rings of spring move up and down forming crests and
troughs.
2 – coloured tape (which represents the particles of the medium)
vibrates up and down without transferring from its place.
3 – the wave propagates in a direction perpendicular to the
vibration of the medium particles.
Conclusion:
1 – the transverse wave is formed of crests and troughs.
2 – during the wave propagation, the medium particles don't move
from their postions, but they vibrate around their rest
positions.
3 – the disturbance in which the particles of medium vibrate
perpendicular to the direction of wave propagation is known as "
transverse wave "
Transverse wave:
It is a disturbance in which the particles of the medium vibrate
perpendicular to the direction of the wave propagation.
The crest:
It is the highest point of the particles of the medium in the
transverse wave.
The trough:
It is the lowest point of the particles of the medium in the
transverse wave.
Water waves are transverse waves?
Because the water particles vibrate in a direction perpendicular
to the direction of waves propagation.
Activity >>> to show the nature of longitudinal
waves.
Materials and tools:
· spring
· colored tape.
· Nail.
Procedures:
1 – fix one end of the spring to a wall using the nail.
2 – tie the colored tape in the middle of the spring.
3 – push and pull the coil rings from left to right.
Observation:
1 – the rings of the spring are too close to each other in some
areas (compressions) and they are far away from each other in other
areas (rarefactions).
2 – the colored tape vibrates round its rest position without
transferring from its place.
3 – the wave propagates along the direction of the vibration of
the medium particles.
Conclusion:
1 – longitudinal wave is formed of compressions and
rarefactions.
2 – during wave propagation, the medium particles don't move
from their rest position but they vibrate around their rest
positions.
3 – the disturbance in which the particles of the medium vibrate
along the direction of wave propagation is known as (( longitudinal
wave )).
Longitudinal wave:
It is a disturbance in which the particles of the medium vibrate
along the direction of wave propagations.
The compression:
It is the area in the longitudinal wave at which the particles
of the medium are of highest density and pressure.
The rarefaction:
It is the area in the longitudinal wave at which the medium
particles are of lowest density and pressure.
Sound waves are longitudinal waves?
Because the medium (air) particles vibrate along the direction
of waves propagation.
Comparison between transverse and longitudinal waves:
Points of comparison
Transverse wave
Longitudinal wave
Definition:
It is a disturbance in which the particles of the medium vibrate
perpendicular to the direction of wave propagation.
It is a disturbance in which the particles of the medium vibrate
along the direction of wave propagation.
Composition:
Crests and troughs.
Compressions and rarefactons.
Examples:
Water waves.
Sound waves.
Note
From the opposite figure:
The crest in transverse wave is equivalent to compression in
longitudinal wave:
Similarly, the trough is equivalent to the rarefaction.
Real life application: >>> physiotherapy tubes
((Jacuzzi)).
· Jacuzzi is a tube where moves in the form of circular
waves.
Uses of Jacuzzi:
Use to treat:
1 – sprains and cramps by using hot water.
2 – Nervous tension by using cold water.
Questions on lesson:
Complete the following statements:
1 – when the tuning fork oscillates , …………………………… is generated
which travels in the form of sound waves.
2 – the molecules of the medium …………………………. During the passing
of waves in the direction of wave propagation without ……………………………..
from their rest positions.
3 – in wave motion, the waves transfer ………………………. From the
vibrating source to the medium ……………………………………. In their propagation
direction.
4 – the mechanical waves are classified into ………………………. And
………………………….. waves.
5 - ……………….. waves need a medium to propagate through, such as
…………………………. And ………………………………… waves.
6 – radio waves are considered …………………. Waves that propagate
through free space with a velocity of ……………………………
7 – transverse wave consists of ………………………… and
………………………………..
8 – the trough is the ………………………….. point of medium particles in
the ……………………….. wave.
9 – the longitudinal wave consists of ………………………… and
…………………………
10 – the crest in the ……………………. Wave is equivalent to the
…………………………….. in the longitudinal wave.
Choose the correct answer:
1 – in wave motion , …………………………….
a. medium particles move b.the waves move carrying the
energy.
c. medium particles vibrate without transferring from their
places. d . b and c correct.
2 - ……………………… is mechanical waves.
a. water wave only b. sound wave only.
c. microwave only d. both a and b
3 – radio waves ……………………….
a. are transverse mechanical waves. B. are longitudinal
waves.
c. propagate through vacuum d. need a medium to propagate
through.
4 – all of the following are electromagnetic waves except
………………………. Waves.
a. light b. sound c. x-rays d. radio.
5 – transverse wave consists of ……………………….
a. compressions and rarefactions b. troughs and
rarefactions.
c. compressions and crests. d. crests and troughs.
6 – all of the following are transverse waves except ……………………..
waves.
a. water b. light c. sound d. radio
7 – the electric bell produces pulses of …………………………
a. compressions and rarefactions. b. crests and troughs.
c. crests and rarefactions d. compressions and troughs.
8 – the highest point of the particles of the medium in the
transverse wave is known as. ……..
a. the crest b. the compression c. the rarefaction. D. the
trough.
9 – Jacuzzi is a tube where water moves in the form of
…………………….. waves.
a. circular b. longitudinal c. oval d. no correct answer.
Give reason for :
1 – sound waves are mechanical waves, while radio waves are
electromagnetic waves?
…………………………………………………………………………………………………………………………………………………
2 – the wave produced due to vibration of a string are
transverse mechanical waves?
…………………………………………………………………………………………………………………………………………………
3 – we see lightning before hearing thunder?
…………………………………………………………………………………………………………………………………………………
4 – water waves are transverse mechanical waves?
…………………………………………………………………………………………………………………………………………………
B : Longitudinal waves
A : Transverse waves:
Transverse and longitudinal waves:
Mechanical and electromagnetic waves:
B: Electromagnetic waves.
A : Mechanical waves
B: longitudinal waves.
A : transverse waves.
Types of waves:
Remember: >>> in wave motion:
** Medium particles don't move from their positions, but they
vibrate only.
** the wave propagates carrying the energy in the same direction
of its propagation.
The concept of wave motion:
The role of waves in transferring energy
Wave motion
