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Port Said International Schools
Better education for future generations
Science Department
Grade: 7
Worksheet 7
Name: ………………………………………. Date: ……………………………………………………
1- Complete the following:
2- Sound waves and water waves are examples of mechanical waves.
3- Water wave is an example of mechanical waves, while light wave is an example of
electromagnetic waves.
4- Thunder sound transfers in a form of mechanical waves, whereas lightning flash
transfers in a form of electromagnetic waves.
5- Light waves can spread out in all mediums and vacuum with velocity of 3*1012 m/s.
2- Choose the correct answer:
1- All of the following are periodic motion except the ………….. motion
a) fan
b) pendulum
c) train
d) sunflower
2- Mechanical waves are characterized by ……………..
a) their speed is greater than electromagnetic waves
b) their speed is 300 million m/s
c) they need a medium to propagate through.
3- We see lightning before hearing thunder because ……………..
a) lightning occurs before thunder
b) sound needs a medium to travel through.
c) the velocity of light is 340 m/s
d) the velocity of light is much greater than that of sound.
3- Justify the following:
1- Circular motion is a periodic motion.
Because it regularly repeated in equal periods of time
2- We receive the sunlight, while we can’t hear the sound of solar explosions.
Because light is an electromagnetic waves that doesn’t need a medium to
travel through and has high speed, while sound is a mechanical wave that
needs a medium to travel through and has low speed
3- We see lightening before hearing thunder.
Because lightening is an electromagnetic waves that doesn’t need a medium
to travel through and has high speed, while thunder is a mechanical wave that
needs a medium to travel through and has low speed
4- What is meant by each of the following?
1- Transitional motion.
Port Said International Schools
Better education for future generations
Science Department
Grade: 7
Worksheet 7
is the motion which the object position is changed in proportion to a fixed frame of
reference from time to time from an initial position to a final one, such as the train motion
– the bike motion – the car motion
2- Periodic motion.
The motion which is regularly repeated in equal periods of time such as:
a. Vibrating motion: such as the pendulum.
B.Circular motion: such as the fan arms
3- Speed.
Distance covered in one second
4- The motion.
It is the change in object’s position as the time passes
5- Give an example indicating each of the following:
1- Translational motion
2- Vibrating motion
3- Circular motion
4- Wave motion
5- Mechanical waves
.train
pendulum
the fan
throw cork on the water
sound waves
6- Compare between mechanical waves and electromagnetic waves.
Mechanical waves
1- Vibration of the medium
particles.
2- It needs a medium to transfer
through.
3- Its speed is relatively slow.
4- Such as: sound waves – water
waves.
Electromagnetic waves
1- Accompanied with the
electromagnetic forces.
2- Spread in all media and space.
3- The speed is extremely great
300milion m/s.
4- Such as light waves – wireless
waves – radio and television waves
– ultra violet and infrared rays
which accompanied by the sun
rays.