Presentation by

Language Assistant – Liannette Bellido Cintrón

Natural Sciences

2˚ ESO

I.E.S. Francisco Rodríguez Marín– OSUNA, SevilleJANUARY 2011

What is sound?Sound is made by an object that is vibrating or oscillating quickly.

• Sound requires:

• An object that is vibrating.

• A substance to carry it.

• A receptor.

How is sound made?Sound only occurs when a object vibrates or oscillates very quickly.

To produce sound, the object must oscillate between 20 and 20,000 times a second. To know if you could hear it, you need to know what frequency the sound has.

Frecuency is:

the scale that measures the different rates at which a body vibrates or oscillates.

The unit of measurement

of frequency is Hertz (s-1).

You can hear a sound if the frequency is bigger than 20 Hz and smaller than 20,000 Hz.

Can you hear a sound that has a frecuency of 1,000 Hz?

YES

Sound needs a medium for propagation

The mechanical vibrations that can be interpreted as sound are able to travel through all forms of matter: gases, liquids, solids, and plasmas.

•

Sound needs air to travel, so it cannot travel through a vaccum.

If you could play the guitar in the Moon would it produce any sound?

NO. Because there is no air in the

Moon, and sound needs a medium of propagation.

1. Sound makes the air vibrate.2. Sound is funnelled into the ear.3. Sound runs by the outer ear.4. The eardrum vibrates and the vibrations are

made bigger by small bones.5. Vibrations are turned into electrical signals by

nerves in the cochlea.6. Electrical signals go to the brain.

Speed of Sound• The speed of sound depends on the medium through which the waves are passing, and is often quoted as a fundamental property of the material.

• In general, the speed of sound is proportional to the elasticity of the medium to its density. Those

physical properties and the speed of sound change with ambient conditions.

Pitch

• A measure of how high or low a sound is• Pitch depends on the frequency of a sound

wave• For example,

- Low pitch

- Low frequency

- Longer wavelength

- High pitch

- High frequency

- Shorter wavelength

Loudness• To create vibrations

energy is used.• The greater amount

of energy used the louder the sound.

• The strength of the changes in air pressure made by the vibrating object determines loudness.

•As the sound spreads out from its source, the concentration of power becomes less.

As the distance from the source increases the amount of power is spread over a

greater area• For us to perceive a sound as twice as loud

its intensity must be ten times greater.• The perceived intensity level of sound is

measured in a scale using a unit called

the decibel (dB) 2

The scale begins on the softest sound that a person can hear. This is called the threshold of

hearing.

The scale ends at the volume that causes pain and is

therefore called the threshold of

pain.

“Timbre” (TAM-ber) or tone color

Is the specific property of sound that enables us to determine the difference

between two sounds produced by different instruments, for example,

between a piano and a harp.

Reflection of sound- When sound encounters an obstacle, the

sound waves bounce off and reflect.

- This causes the phenomenon called…

ECHO

Noise pollution• Urban areas are the most affected by the noises

emitted by cars, machinery, traffic, airplanes, etc.

• You can avoid exposure to noise pollution by using special protection.

Scientists recommend avoiding exposure to noise higher than 65dB.

To control noise pollution, governments have adopted various alternatives.

Acoustic walls

THANK YOU FOR YOU ATTENTION!