The Energy of Waves
Section 1: The Nature of Waves
 Student objectives
 Describe how waves transfer energy
without transferring matter.
 Distinguish between waves that require a
medium and waves that do not.
 Explain the difference between transverse
and longitudinal waves.
Vocabulary
Please add the following words to
your SNB glossary
Waves
Medium
Transverse waves
Longitudinal waves
Light waves from the sun
Water waves
in the ocean
Microwaves
inside the
microwave
oven
Radio waves transmitted to the
radio
Sound
waves
from the
radio
Sounds waves from
The
telephone
ringing
And the
voices on the
phone
What do all waves have in
common?
 All waves are disturbances that
transmit energy.
 Energy can be carried away from its
source by a wave.
 As a wave travels, it does work on
everything in its path.
 The material through which the wave
travels does not move with the energy
Remember when we talked about
Light Energy
Sound Energy
 Is produced by the
 Is caused by an
vibrations of
electrically charged
particles. Light
vibrations cause
energy to be
transmitted (in
waves).
object’s vibrations
which transmits
energy through
the air around it
(in waves)
But what’s the difference?
 Most waves transfer energy by the vibrations of
particles in a MEDIUM.
 A medium is a substance through which a wave
can travel. A medium can be a solid, liquid, or
gas.
 Sound waves NEED a medium.
 Other wave that need a medium are ocean
waves and earthquakes.
 WAVES THAT NEED A MEDIUM ARE
CALLED MECHANICAL WAVES.
 Light waves are electromagnetic waves,
which do not need a medium. Light can
travel through the vacuum of space.
SOUND CAN’T!
 Misconception
ALERT!
 You may believe that sounds can be heard
in a vacuum (like outer space). In many scifi movies, explosions and other sounds are
heard in outer space. THIS IS
SCIENTIFICALLY INACCURATE!
Energy transfer without a medium
 Some waves can transfer energy
without going through a medium:
 Visible light, microwaves, TV and
radio signals, and X rays.
 WAVES THAT DO NOT NEED A
MEDIUM ARE
ELECTROMAGNETIC WAVES
WERE YOU PAYING ATTENTION?
How do electromagnetic
waves differ from mechanical
waves?
Electromagnetic waves do
not require a medium.
Cup-and-string phone
 Punch a small hole in the bottom of your cup.
 Push the ends of a long piece of string through the





bottoms of each cup.
Tie paper clips to the ends of the strings inside the
cups
Have a partner take one cup and you take the other.
Move away from each other until the string is tight.
To talk, hold the rim of the cup around your mouth
and speak clearly. To listen, hold the rim of the cup to
your ear.
How does the cup-and-string phone transmit sound
waves?
Answers to Ch.1 Sec.4 pg.27
1)Sample answers:
 Volume is the amount of space taken up by matter.
 Density is the amount of matter in a given volume.
 Mass is the amount of matter an object contains.
2) C
3) Sample answer: Mass and density are related because in order
to calculate density, the mass and volume of an object must be
known. Density tells how much mass is in a certain volume.
4) The normal body temperature is 98.6 °F and 37°C.
5)1100÷0.5 = 2200
6) You would see eye protection, clothing protection, hand safety,
and chemical protection because acid is corrosive and will
cause severe burns if it come in contact with eyes, skin, or
clothing.
Fun Fact:
Light travels 300,000,000 m/s.
1 second = 1,000,000,000 nano
seconds
This piece of string is how far light
can travel in 1 nanosecond!!!
This piece of string is 30 cm long
Types of Waves
 Particles in Transverse waves vibrate in an upand-down motion.
 The particles in this kind of wave move
perpendicularly to the direction the wave is going.
 CREST- the highest point of a transverse wave.
 Trough- the lowest point between each crest of a
transverse wave
 **Although electromagnetic waves do not travel by
vibrating particles in a medium, all
electromagnetic waves are considered transverse
waves.
 In longitudinal waves, the particles of the medium
vibrate back and forth along the path that the
waves moves.
 Compression- a part of a longitudinal wave where
the particles are crowded together
 Rarefactions- a part of a longitudinal wave where
the particles are spread apart
 Sound waves are examples of longitudinal waves.
 Sound waves travel by compression and
rarefactions of air particles.
 Now, turn to page 578 and draw and label figure
6 into your SNB
Were you paying attention?
What kind of wave is a sound
wave?
A sound wave is a longitudinal
wave.
POP Quiz!!!
Clear off your desk
Take out a sheet of paper
Number 1-5
Label your paper with your
name and Chapter 20 section 1
Pop Quiz
1. A wave is a disturbance
that travels through
________
2. A wave carries
_________.
3. Waves that require a
medium are called
___________
4. Waves that do not
require a medium are
called __________
5. In a _________, the
particles vibrate back and
forth along the path that the
waves moves.
1. Mechanical waves
require a _________
through which to
travel.
2. Any __________
transmits energy
through vibrations.
3. In a _____________, the
particles move perpendicularly
(up and down) to the direction
that the wave travels.
4. Waves transfer
_______________.
5. What type of wave
does not require a
medium?
True or False
1. Light waves are
mechanical waves because
they must travel through a
medium.
True or False
2.In space, no one
can hear an
explosion.
How’s that Sound?
 With this lab you’ll find out if sound travels better through a gas, a
liquid, or a solid.
 Scientific Method
 1) Make an observation
 2) Ask a Question- Does sound travel best through a gas, a
liquid, or a solid?
 3) Formulate a hypothesis. What do you think? Write your own
hypothesis.
 4)Test the hypothesis.
CAUTION! - DO NOT POP the bag of water . Also, you will be
to remain very quiet to complete this lab!!!!!!
5) Analyze your data
6) Write a conclusion
7) Share your findings