Science
Monday (15/2) – Read and save the following
content based on sound. Answer the questions (given in your note book) as
discussed in class on the following days.
Sound
Every day, we hear natural sounds, like the wind, and other noises
such as from cars and aero planes. We also put together different sounds.
Sound is a form of energy. It is made of vibrations
(back-and-forth movements) that can move through air, solid things and liquids,
but not through empty space.
Making sound: sounds are made when things
vibrate. They make air vibrate, too. The vibrations spread through the air in
waves. We hear the sound when the waves enter our ears. When we hit a drum,
speak or clap, molecules in air vibrate.
Sound travels through different materials
The speed of sound depends upon the properties of the medium it is
passing through.
Gases:
When we look at the properties of a gas, we see that only when
molecules collide with each other then the sound wave move about.
Speed of sound in air is 340m/sec.
Liquids:
Sound travels faster in liquids than in gases because molecules
are more tightly packed.
In fresh water, sound waves travel at 1,482 m/second .
In salty water, sound waves travel at 1500m/sec.
That's over 4 times faster than in air.
Several ocean-dwelling animals rely upon sound waves to
communicate with other animals and to locate food and obstacles. The reason
that they are able to effectively use this method of communication over long
distances is that sound travels so much faster in water.
Solids:
Sound travels fastest through solids. This is because molecules in
a solid medium are much closer together than those in a liquid or gas, allowing
sound waves to travel more quickly through it. In fact, sound waves travel over
17 times faster through steel than through air. The exact speed of sound in
steel is 5,960 meters per second (13,332 mph).
Loudness is measured in decibels. Very loud sounds can damage
ears. The loudest sounds, such as rocket lift- off (180 decibels), will damage
your ears.
Loud and quiet sounds: big
vibrations in the air have lots of energy. They sound very loud. Small
vibrations in the air have much less energy. They sound very quiet.
Hindi
Learn Question Answers of Lesson -12 written
in Hindi notebook for a review on Tuesday, 16/02/16.
