1. sound
By Miss Buicke

2. What we must know from the syllabus
OP40
Show that sound is a form of energy, and understand that sound is produced by vibrations
OP41
Show that sound transmission requires a medium and that echoes are reflected sound
OP42
Understand that the ear detects sound vibrations and that exposure to very loud sounds can cause damage to hearing

3. OP43
Recall that the speed of sound is less than the speed of light.
OP44
Explain the time lag between seeing and hearing the same event.

4. Sound is a form of energy
To show that sound is a form of energy you must be able to show that it can do work (because energy is the ability to do work).
Work is done when an object is being moved. So we need to show that sound can move something.

5. To demonstrate that sound is a form of energy
Equipment: speaker, balloon, piece of string ,
retort stand and clamp.
method:
Hang the balloon with the piece of string on
the retort stand.
Switch on the speaker and observe what
happens.
Result
The balloon is seen to move.

6. Result:
The balloon is seen to move.
Conclusion:
The kinetic energy of the moving balloon
came from the sound energy from the
speaker.
Sound is a form of energy

7. We now know that sound is a
form of energy but what
actually causes sound to
be made?
Lets try and figure out the answer!
If we were to put our hand on a speaker as
music is being played what would we feel?
Answer: We would feel a vibration

8. Produced when objects vibrate
Sound:
Produced when objects vibrate
Examples of sound made by vibrations
When you pluck a guitar string it vibrates
and consequently makes a sound.
Hold one end of a plastic ruler firmly on the
edge of a table. Bend the other end
downwards. When you release the ruler it
vibrates and makes a sound. This is one
vibration you can see.

9. Musical instruments

10. What do sound vibrations look like?
Sound vibrations can be quite fast and we
cannot see them. In order to visualize what a
sound wave looks like think of a slinky. When a
slinky moves a sound wave makes a similar
movement.

11. How sound travels.
When we have a conversation with a friend there are many things
happening which we don’t realise.
For example laura is talking to Naomi. How exactly does
the sound travel?

12. Emma’s vocal chords will vibrate.
The air molecules in Emma’s mouth will vibrate.
When Emma’s opens her mouth the vibration energy is passed onto the air molecules in the room. The air molecules in the room are vibrating.
The air molecules in Naomi’s ear canal will vibrate and knock against her eardrum

13. Diagram of the ear

14. experiment To show sounds needs a medium to travel through.
Equipment: electric bell, bell-jar and vacuum pump.
Method:
An electric bell is placed in a bell-jar
Turn on the bell. Its sound can be heard clearly when there is air in the bell -jar.
Remove air from the bell-jar using a vacuum
pump.
The bell can be no longer heard but it can be seen ringing.

15. Result: when the air was removed the bell could
no longer be heard
Conclusion: sounds needs a medium to travel through

16. Reflection of sound.
The reflection of sound is where sound waves bounce
off a surface. A suitable surface to reflect sound
would be a smooth, hard surface, e.g. a wall.
An echo is an excellent example of sound reflection.
If you stand back from the face of a cliff and shout
you will hear your own voice reflect off the cliff face.

17. Interesting fact:
Did you know bats use echo’s to find food?
Bats send out sound waves using their mouth or nose. When the sound hits an object an echo comes back.
The bat can identify an object by the sound of the echo. They can even tell the size, shape and texture of a tiny insect from its echo.

18. Most bats use echolocation to navigate in the dark and find food.

19. Ultrasound Ultrasounds are an example of the reflection of
sound. Ultrasound is a high-frequency sound which
cannot be heard by the human ear.
Ultrasound echoes are used by ships to determine
the depth of the sea below them. The ship emits an
ultrasound pulse and notes the time taken for the
pulse to return

20. A person stands 340 m from a vertical wall.
Calculation:
A person stands 340 m from a vertical wall.
He shouts loudly. It takes 2 seconds for the
sound to return using a stopwatch.
Find the speed of sound.
Formula: distance= speed x time
distance to and from the wall
speed =
time taken

21. 680 2
Speed= 2 =
= 340m/s

22. Comparing the speed of sound and the speed
of light
The value of the speed of sound in air is
340ms-1.
The value of the speed of light is air is
ms-1
There is a big difference between the two
values of speed. The speed of sound is less then the speed of light.

23. Thunder and lightning is an excellent example to use in order to compare the two speeds.
Thunder and lighting both happen at the same time. we see the lightning first and then a few seconds later we hear the thunder.

24. The human ear and loud sounds.
The human ear can hear sounds that are
very faint and sounds that are very loud.
Each sound has its own unique sound level
which can be measured on a sound level
meter.
Sound level is measures in decibels.

25. Some values of everyday sound levels
Source of sound or noise
Sound level (in decibels)
Ordinary conversation 60
Busy street traffic 70
Average wisper 20

26. As the decibel level rises, the danger of
Ear protection
As the decibel level rises, the danger of
hearing damage increases. Regular exposure
to sound above 70 decibels can be harmful
If ear protection is not used.
People working in noisy environments should
use ear protection.
Ear protection sign