SOUND

CLASS: 8 SUBJECT : SCIENCE

U - 6 : SOUND

SOUND WAVE

• A sound wave is a vibration that travels through a solid, liquid or gas such as the air or water.

• When there is a sound wave, the air particles don’t travel directly from the object making the sound to your ear. Sound waves are vibrations being passed on between particles.

• The particles vibrate in the same direction as the wave travels. Sound is an example of a longitudinal wave.

The loudness of a sound depends on how big the vibration of the air is.

• If air particles move back and forth a lot we hear a loud sound.

• If the source of a sound makes the particles vibrate more gently, we hear a quieter sound.

​LOUDNESS

​The pitch of a sound depends on how quickly the air vibrates.

• When air particles move back and forth quickly we hear a high pitch sound.

• When the air vibrates less quickly we hear a low pitch sound.

The number of vibrations each second is called the frequency and is measured in a unit called hertz (Hz).

The lowest pitch sound that most humans can hear is 20 Hz.

The highest pitch sound the average human can hear is 20,000 Hz.

​PITCH AND FREQUENCY

​To record or analyse a sound, scientists and musicians use a microphone to turn the sound into an electrical signal.

The electrical signal can then be displayed on a device called an oscilloscope and it produces a graph called a wave trace.

Multiple Choice

What type of wave is a sound wave? 

• Transverse Wave

• Longitudinal wave

• Tidal wave

• Light wave

Multiple Choice

What is the lowest frequency a human can hear ? 

• 30 Hz

• 2 Hz

• 20 Hz

• 20,000 Hz

Multiple Choice

Sound waves travel the FASTEST through _____________.

• gases

• liquids

• solids

• vaccum

Multiple Choice

What is frequency?

• the number of vibrations per second

• how high or low a sound is

• the loudness or softness of a sound

• the back and forth movement of matter

Multiple Choice

Which of the following is the inverse of time period?

• Amplitude

• Frequency

• Pitch

• Quality

Multiple Choice

Sound does not travel in space because

• Space is too far away.

• There is no matter in space.

• Space is the final frontier

• Space has planets.

Multiple Choice

Speed of light in air is:

• 5100 m s^-1

• 3*10⁸m s^-1

• 330 m s^-1

• 3*10¹⁰ m s^-1

Multiple Choice

Ryan makes an instrument from a drinking straw as shown. If he cuts the straw in half, what will happen to the pitch?

• decreases

• it will remain the same

• increases

• 
  there is no sound

Multiple Choice

High pitch sounds are caused by a ______ vibration

• fast 

• slow

• hard

• sharp