1. World of Sounds Sound and its properties

2. What produces sound? Some objects produce sounds when they move. For example when we pluck a string on a guitar, it produces a sound. The movement of a string is called vibration. When objects vibrate they produce sound. For example if we touch them, hit them, bump into them or if they fall into the floor.

3. How do we perceive sounds? 1 Outer ear:The outer ear is the part you see when you look in the mirror. The outer ear catches the sound traveling in the air. It then moves the sound to the part of the ear inside the head. 2 Eardrum: Sound travels from the outer ear to the eardrum. The eardrum is the thin, skinlike layer that covers the middle part of the ear. When sound hits the eardrum, the eardum begins to vibrate 3 Threee tiny bones (hammer, anvil, stirrup): The vibrating eardrum makes the three tiny bones in the middle ear vibrate. 4 Part shaped like a shell (cochlea): It is filled with liquid. The vibrating bones cause the liquid to vibrate. 5 Nerve to the brain: The liquid carries the sound vibrations to a special nerve. This nerve carries messages to the brain. The brain helps you understand the sound you hear.

4. Types of Sound There are many different sounds. For example the sound of a sneeze is very different from the sound of an applause. Sounds are different from one another in their tone and intensity. Depending on their intensity sounds can be loud or soft. Loud sounds like the honk of a truck’s horn, are intense, they have a high volume. Soft sounds, like the pages of a book turning have low intensity and a low volume.

5. Depending on the tone sounds can be sharp or low. The sound of a doorbell is sharp, the sound of a drum is usually low. The tone (sharp or low) depends on how fast the object vibrates. The faster an objects vibrates, the sharper the sound will be and viceversa.

6. Materials and sounds Sound does not always propagate at the same speed. For example, it propagates much faster in water than in air, this is because water conducts sounds much better than air. There are materials that conduct sound very well like metals. Other materials do not conduct sound well, like cork. They are used as sound insulators.

7. Sound propagates… Sound propagates in all directions. As a result we can hear a radio that is turned on in one room of the house in all the other rooms. Sound propagates at great speed. As a result, we hear the sound of a train before it passes us.

8. What’s the difference between sound and noise? Sounds: produce regular soundwaves,harmonic, pleasant to the ear. Noise: produces irregular soundwaves, unpleasant and disturbing to our ears.

9. A decibel meter helps us know how loud and dangerous a sound can be for human ears. Lound sounds are a form of pollution called sonic pollution. How can we measure the intensity of a sound? The intensity of a sound is expressed in decibels (dB).

10. How loud can sounds be? Threshold of pain: decibel level at which a person can become deaf by having his/her eardrums explode.

11. Partially deaf people use hearing aids to help them perceive sounds better, they use a device that amplifies sounds People who are completely deaf use sign-language to communicate with others What about people who are totally or partially deaf?

12. How do we use sounds? We communicate through sound, the telephone transmits our voice to people who are far away. We can also use sound to emphasize situations or actions, like in movies (specially horror movies!!).

13. We also use instruments to make music. There are 3 principal kinds or types of instruments: String instruments

14. Percussion Instruments Percussion instruments produce sounds because they vibrate when you strike them. Drums and cymbals are percussion instruments.

15. Wind instruments Wind instruments produce sounds when we blow them because the air inside them vibrates. French horns and oboes are wind instruments.

16. Quiz How are sounds different from one another? What types of musical instruments are there? How does each instrument produce sound?

17. Why can we hear sounds produced far away from us? What happens when sound bumps into an obstacle? Does sound always travel at the same speed? Quiz