Port Said International Schools
Better education for future generations
Science department
Worksheet 3
Grade: 8
Name:…………………………….
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1 )Complete the following
1-Examples of periodic motion are(wave motion)…and(oscillatory motion)
2-The complete oscillation contains …(4) amplitudes.
3-The frequency is the(reciprocal).of periodic time.
4-The measuring unit of frequency is (Hertz)
5- Waves are classified according to the ability to propagate into(mechanical).wave and …
(electromagnetic)wave
6- Waves are classified according to the direction of vibration of medium particles into
transverse)wave and(longitudinal) wave
7-The transverse wave is formed of(crests)..and…(troughs)….
8- The longitudinal wave is formed of(compressions)..and(rarefactions)….
9-Sound waves need medium to propagate so it(mechanical).waves
10- Sound waves are(longitudinal).while water waves are(transverse)……
2) Write the word(s) that means each of the following statements:
1-The motion is repeated through equal intervals of time
( periodic motion )
2-The the movement made by the oscillatory body when it passes a single point in its path of
motion, two consecutive times in the same direction
( complete oscillation)
3- The maximum displacement achieved by an oscillatory body away from its point of rest.
( amplitude
)
4- The time needed by the oscillatory body to make-a complete oscillation. ( periodic time
5- The number of complete oscillation in one second.
( frequency
6- The measuring unit of frequency
( Hertz
7- The motion produced as the resulted of the vibration of the particles of the medium in a certain
point and in a certain direction.
( wave motion
8- The disturbance that propagates and transfers energy in the direction of the propagation.
( wave
9- The direction of progression of the wave.
( line of propagation
10- They don't need a medium in order to propagate so they can propagate in space.
(electromagnetic
waves
)
11- They need a medium in order to propagate so they can't propagate in space.
( mechanical waves
12- The disturbance which causes the particles of the medium to vibrate perpendicular to the
direction of wave propagation.
(transverse waves
13- The disturbance which causes the particles of the medium to vibrate along to the
direction of wave propagation.
(longitudinal waves
14- The waves which are formed of crests and troughs.
( transverse wave
15- The waves which are formed of compressions and rarefactions
( longitudinal waves
18- It's the highest point in a transverse wave with respect to the horizontal.(crest
19 -It's the lowest point in a transverse wave with respect to the horizontal. ( trough
20- It is the point of highest density and pressure in longitudinal wave.
( compression
21- It is the point of lowest density and pressure in longitudinal wave.
( rarefaction
22- It's the distance between two consecutive crests or troughs on transverse wave (wave length
23- It's the distance between two centers of two consecutive compressions or rarefactions on
longitudinal wave
( wave length
24- It's the distance covered by the wave in one second.
( wave velocity
25- It's the number of waves passing a certain point in one second. ( frequency
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3)Choose the correct answer:
1-The velocity of the oscillating body…………………,when it passes the point of rest.
( increases – decreases – doesn't change )
2- The velocity of the oscillating body…………………,when it moves away point of rest.
( increases – decreases – doesn't change )
3- As the velocity of the oscillating body decreases , its kinetic energy
( increases – decreases – doesn't change )
4-All the following examples of oscillatory motion except………..
( tuning fork – stretched string - rotary bee )
5-Frequancy X periodic time = …………
( 1 - 2 - 0.5 - 0.2 )
6- The frequency of an oscillatory body makes 36000 complete oscillations in 6 min is ….Hz
( 6000 - 100 - 1000 - 600 )
7-If frequency of an oscillatory body 10 Hz, so it takes ……seconds to make complete oscillation.
( 600 - 6 - 1/10 - 60 )
8- If frequency of an oscillatory body 20 Hz, so it makes……….. complete oscillations in half
minuets.
( 20 - 1200 - 10 - 600 )
9- If frequency of an oscillatory body 2 Hz, so it takes ……seconds to make one complete
oscillation.
( 2- 0.5 - 5 - 1 )
10- The distance between the center of the third compression and the center of the fifth
compression on the wave propagation is 30cm so the wave length is ………cm.
( 30 - 15 - 60 - 10 )
11-If the wave velocity is 100m/s and its frequency equals 200Hz so its wave length equals …..
( 0.2 m - 0.5 cm - 0.5 m - 2 m )
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4)-1-Choose from column(B)what suit in column(A):
A
B
1-periodic time
a-is measured by meter
2- amplitude
b- is measured by m/s
3-frequency
c- is measured by m/s2
4-wave velocity
d- is measured by second
e- is measured by hertz
1-d……………………………………………..............................................
2-a…………………………………………………………………………….
3-e…………………………………………………………………………………
4-b…………………………………………………………………………………….
5) What's the periodic time and the frequency for the oscillating body
in the opposite figure.
The time needed for making one amplitude is 5 sec.
So;the time needed for making 4 amplitudes is 5x4=20 sec
Periodic time =20 sec
Frequency =1/periodic time=1/20=0.05Hertz
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5 sec
6)In the opposite figure ,the ball of the pendulum moves from (x) to (y) in 0.04 .
Find the frequency and periodic time
….the motion from x to y represents 2 amplitudes
Which equals half oscillation
So, the time needed to make one complete oscillation is
2x0.04=0.08sec
Periodictime =0.08sec
Frequency=1/0.08
=12.5 hertz
-----------------------------------------------8m
7)From the opposite figure .find:
1- wavelength
4
secs
ec
2-frequency
3-amplitude
4-wave velocity
1-Wave length=the distance between 2 successive crests
If the distance between first and third crest =8 m
So, the wave length =8/2=4m
2-Frequency=1/periodic time
The time which is needed to make half oscillation is 4 sec
So periodic time=4x2=8sec
Frequency=1/8=0.125Hertz
3-amplitude=1 m
4-wave velocity=v=f x ʎ
V=0.125 x 4= 0.5 m/sec
8-From the opposite figure .find:
1-frequency
2-amplitude
3-periodic time
Amplitude=1 meter
periodic time=time needed to make one complete oscillation =4 sec
frequency = 1/t
=1/4
=0.25Hertz
(t)