sound By Miss Buicke

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

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.

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.

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.

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

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

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.

Musical instruments

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.

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?

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

Diagram of the ear

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.

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

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.

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.

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

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

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

680 ---------- 2 Speed= 340 +340 ------------------- 2 = = 340m/s

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 300 000 000ms-1 There is a big difference between the two values of speed. The speed of sound is less then the speed of light.

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.

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.

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

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