Lesson 3

1 What did you do last time? 2 medium vacuum particles vibrations ear sound PRINT the word next
to the image on the next slide.
Sound - L3 ear par vib sou vac med
4 1 The person in the center of
a circle is IT and should shut his/her eyes or be blindfolded.
Do you need two ears to locate a sound?
Test it!
You can do this with ONE other person or in a group. The Sound Game!
5 Can the person who is IT still tell where soft sounds are coming from? 2 1 Locating Sounds Repeat making softer
and softer sounds.
Someone in the outside circle makes a short sound.

Can the person who is IT point to where the sound is coming from?
6 Can the person who is IT
still tell where soft sounds
are coming from?
Now have the person who is IT
cover up one ear with his/her hand
or use an ear plug to block the sound.
A sound almost always reaches one ear slightly before it reaches the other.
Your brain uses this information to figure out the location of the sound.
When you block the sound to one ear, this becomes more difficult to do.
You can pinpoint where most sounds are coming from
because you have TWO ears.
3 4
Is sound a liquid or a gas? NO!
Is sound any form of matter? NO!
8 Matter is Made of Particles Animation of Particles Correction: Particles in solids DO move. They jiggle and vibrate! WAIT, BEFORE YOU GO ON,
it's time for a 2 minute REVIEW -- of a KEY IDEA!
9 casserole dish
or metal cake pan
Find these items: flashlight
spoon What ARE sound waves?
To visualize what sound waves look like,
begin by making waves in water.
Sound travels in WAVES.
10 What happens to the surface of the water Bang the spoon
on the side of
the casserole dish
or rectangular cake pan.
To better see
the results,
shine a
bright light
from above.
3 Sound and Waves Set the dish or pan
on a flat surface.
Fill the casserole dish
about half full with water.
Click for
Do you see waves moving across the water inside the dish?
The waves bounce off the sides in almost straight lines.
Did they collide in the center?
1 2
Sound vibrations
travel in waves.
Sound waves are ... LONGITUDINAL WAVES!
12 WHAT is a longitudinal wave? To understand
longitudinal waves,
you will need a slinky.
Rest the slinky on a flat surface.
Stretch it out. DON’T PULL TOO HARD.
Either anchor it at one end or
have a friend hold at one end.
1 2 Press together the first few coils
of the slinky and then release them.
Watch as the COMPRESSION
travels down the slinky.
13 The moving
is followed by
the spreading apart
of the springs.
Do you see the COMPRESSION (tightly coiled area)
as it moves down the slinky?
4 Longitudinal Wave
14 Even though the compression wave moves forward down the slinky,
each individual coil on the slinky travels very little.
Longitudinal Wave Notice the DIRECTION that each spring is moving:
first to the right a little,
then backward to the left
toward its original position.
AGAIN, the wave travels from left to right AND
each spring moves from left to right and back again.
15 Longitudinal Wave Longitudinal Wave The motion of the compression wave AND
the motion of each spring
are along the SAME direction, left to right.

16 Longitudinal Wave Sound Vibrations in Air
The compression wave moves forward
THROUGH the gas particles from left to right.

The gas (air) molecules, like the slinky coils, move very little.

AND the molecules move forward to the right
and back again.
Sound vibrations moving through air are similar to the slinky.
17 Animation courtesy of Dr. Dan Russell, Grad. Prog. Acoustics, Penn State So it is with sound waves.
Even though sound waves
can travel very far,
the particles themselves only move a small distance.
Watch how the motion moves
or propagates down the line
in the animation.
Though the WAVE moves along the entire line,
each stick man only stands up and sits down.
18 Animation courtesy of Dr. Dan Russell, Grad. Prog. Acoustics, Penn State This animation models sound waves moving
through particles of air.
The compression waves are moving from left to right.
Now watch a red particle.
Notice that it moves only a small distance:
back and forth, back and forth, from left to right, and back.
19 Click for answer. A physical medium can be
a solid, a liquid, a gas or even a plasma!
REMEMBER: So, if you could put your ear
right next to the Sun, a plasma,
What is a physical medium Sound is a longitudinal wave
in a physical medium.
20 Sound Waves 21 WHY does sound travel through a solid WHAT is a
longitudinal wave
Does sound travel at
the same speed in all materials
HOW quiet is it
on the surface of the Moon and WHY
1 2 3 4 5 Does sound
require a medium
VERY QUIET. The Moon has no atmosphere. Solids are made of particles.
Sound waves require particles.
The particles vibrate along the same direction as the wave is moving. NO! Sound travels fastest in solids, because the particles are packed closer together. YES! Solid, liquid, gas, plasma