Sound and Light
Chapter 17
Lesson 1: What is Sound?
Lesson 2: What is Light?
Lesson One Vocabulary
 Vibration- a back-n-forth
movement of matter
 Volume- the loudness of a sound
 Pitch- how high or low a sound is
 Frequency- the number of
vibrations per second
Lesson 1: Sound
 Sound is energy that travels through the
air.
 A vibration is a back and forth movement
of matter.
 The vibrations make the air vibrate and
this is what you hear.
Lesson 1: Sound
 The loudness of a
sound is called
volume.
 Volume is measured
in decibels (dB).
 A high decibel sound
is loud and has a lot
of energy.
Lesson 1: Sound
 Sound waves move through
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the air as waves.
Some sounds are high
while other sounds are low.
A sound’s pitch is how high
or low the sound is.
The number of vibrations in
a second is the frequency
of a sound.
Frequency and pitch are
related.
A sound with high
frequency has a high pitch
and a low pitch has a low
frequency.
Lesson 1: Sound
 Sound waves move in all directions from an
object.
 A sound that hits a
hard surface bounces
back and it called an
echo.
 You can often hear
echoes in caves
and canyons.
Lesson 1: Sound
 Sound waves move like dominoes; when you
push one, the next one falls down.
 Sound waves move this same way.
 They travel through the air because particles in
the air give energy to the ones nearby.
 Sound can travel a long distance
but the particles stay in the
same place.
Lesson 1: Sound
 Any kind of matter can
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vibrate and carry sound.
Matter that carries sound
is called a medium.
Sound waves need a
medium to travel.
The speed of sound
depends on the medium.
Sound travels fastest in
solids and slowest in
gases.
Sound also moves faster
when it’s warm that when
it’s cold.
Lesson 1: Sound
 Animals can hear sounds
that humans cannot hear.
 Dogs can hear high
pitched sounds.
 Bats have excellent
hearing and when they fly
they produce sound
which bounces off
objects.
 The bat can hear its
echoes and this allows
the bat to fly in the dark.
Cool!
Lesson Two Vocabulary
 Reflection- the bouncing of heat or light off an object
 Opaque- Not allowing light to pass through
 Translucent- allowing only some light to pass
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through
Transparent- A material that allows light through
Refraction- the bending of light as it moves from
one material to another
Concave lens- a lens that is thicker at the edges
than it is a the center
Convex lens- a lens that is thicker at the center than
at the edges
Lesson 2: Light
 Light is a form of energy that travels in waves.
 Unlike sound, light does not need a medium to
travel.
 Light is part of the electromagnetic spectrum
and the part that
we can see is called
visible light.
 The waves that make up
the spectrum have different
frequencies.
Lesson 2: Light
 Light waves are different
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from sound waves.
Light waves move like
ocean waves because
they move up and down.
Light waves can travel
through matter or through
empty space.
Light moves thousands of
times faster than sound.
It only takes 8 minutes for
light travel from the sun
to Earth.
Lesson 2: Light
 You can feel energy in
sunlight as heat.
 You can also feel the
heat from a light bulb.
 The sun and the light
bulb both send out light in
all directions.
 But a laser gives off light
in a narrow beam which
is very powerful because
the waves are close
together.
Lesson 2: Light
 When light hits an object, the objects
affects the path of the light.
 The object can absorb the light, make it
bounce back, or let it pass through.
Lesson 2: Light
 Reflection occurs
when light bounces
off a surface.
 In most cases, light
spreads out when it
is reflected.
 But a smooth surface
does not spread out
and this is why you
can see yourself in a
mirror.
Lesson 2: Light
 Most objects absorb
some light and reflect the
rest.
 Opaque materials do not
let any light pass through
them.
 You cannot see through
opaque objects.
 Most objects around you
are opaque, like you
shoes, your desk, and a
book.
Lesson 2: Light
 Transparent materials let
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light pass through. Most
kinds of glass are
transparent.
Translucent materials
only let some light pass
through.
Stain glass windows are
translucent.
The difference between
transparent and
translucent is how they
spread out light.
Translucent materials
spread more light.
Lesson 2: Light
 When light moves from
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one material to another, it
bends.
This bending is called
refraction.
Refraction changes the
angle at which you see
things.
Have you ever looked at
a straw in a glass of
water?
It seems to bend where
the straw enters the
water. This is refraction.
Lesson 2: Light
 A convex lens is
thicker at the center
that it is at the edges.
 It bends light waves
to bring them
together.
 A convex lens makes
images bigger.
Lesson 2: Light
 A concave lens is thicker at the edges.
 This lens spreads light waves apart.
 This lens makes an object look smaller.