Sound Physics IGCSE

Sound

​By Muhammad Arief Kurniawan
Mutiara Harapan Islamic School

​Making sounds

​all sounds are caused by something vibrating.

​Hearing sounds

​Vibration can happen by hitting, plucking, bowing and blowing.

But how the sound arrive on us (our ear) ?

​The air molecules also vibrating because of the speaker

​The air molecule also effect our eardrum to vibrate.

Drag and Drop

​ We know from previous lesson, sound is one of the ​

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. The sound energy travels as a ​

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. From the previous slide, we can understand that the sound need​

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molecule as a medium so it can arrive on our ​

Placeholder

. Medium means similar as we need ​

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so our car can travel.

Drag these tiles and drop them in the correct blank above

energy

wave

air

eardrum

road

​Thats why...

​Space is very quiet. Because there is no air particle/ molecule in space (vacuum).

​It means the sound wave can't travel in space because it has no medium (road).

Sound energy travel as a wave.

​The physicist give a name to that wave. sound travel as a longitudinal wave.

longitudinal means the wave travel in same direction (parallel) as the particle vibrate.

If the sound wave travel from left to right,
the air particle also vibrating left and right.

Sound energy travel as a wave.

REMEMBER!!
The air particles (dots) is not moving. they just vibrating left and right. look at the red dots.

but, The ENERGY (sound wave) is moving from left to right.

Open Ended

Critical Thinking question alert!

You understood how the sound wave travel through the air particle. So from the picture, write a definition of compression and rarefaction.

​Critical thinking alert!
Why we see the lightning first,
then we hear the thunderclap?

​YES...

It because the light wave's speed is much faster than the sound wave.

​The light travels in light speed, approximately 300 000 000 m/s (300 million metre per second).

And the sound travels 330 - 350 m/s in air depends on the temperature and humidity in the place we measure.

So the sound approximately travels 1 km (1 000 m) by 3 seconds.

Fill in the Blank

A boy sees lightning and hears the thunderclap 9 seconds later. Calculate how far away is the storm.

​Echo... Echo... Echo...

​an Echo is a reflected sound wave.

​Seeing sound

​We use a cathode ray oscilloscope (CRO) to see sound.

​It means we translate the actual wave (physical form) to the mathematical form (as we always do).

​We translate the wave into sinusoidal wave. It just one kind of wave in mathematics (you will learn it when study trigonometry in mathematics).

​Reading the oscilloscope

We can measure 2 things here.

The amplitude and the frequency.​

​amplitude means the greatest height or depth from its undisturbed position

frequency is the number of vibrations per second.
(read: how many vibrations happen in 1 second).
the unit is 1/s or Hertz (Hz).

read this oscilloscope please...

This oscilloscope is set at 20 ms/div.

It means each division in the grid (one box) represents 20 ms (0.02 s).

​the time for one vibration marked as T, which is two boxes (2 x 0.02) so the time for one vibration is 0.04 s.

So amount of vibration in 1 seconds can calculate by 1/0.04 equals to 25 vibrations per second (25 /s).
so the frequency is 25 vib/s or 25 Hertz (25 Hz).

​adjusting the frequency and amplitude

amplitude means amount of energy. For the sound,
low amplitude means quiet sound (sound's volume is low),
high amplitude means loud sound (sound's volume is high).

frequency means character. For the sound,
low frequency means low pitch (low octave sound note),
high frequency means high pitch (high octave sound note).

Open Ended

critical thinking alert!

Which sound will damage your ear? and why?

​Ultrasound

Young humans can hear sounds from 20 Hz to 20 000 Hz.

ULTRASOUND means sounds with frequency more than 20 kHz.
(we can't hear it).

​But, since we SMART, we can use ultrasound for other advantages, like:

​sonar radar

ultrasonography (usg)

Reorder

THANK YOU!! but still, critical thinking alert!

Sound needs medium (particle) to travel. Combining with your understanding on previous lesson about particle formation (state of matter: solid, liquid, gas), write the order where the sound wave will travel fastest to lowest

• Solid

• Liquid

• Gas

1

2

3

• 1
• 2
• 3