Lesson 2

What did you do last time?

eardrum

cochlea

sound

vibrations

ear

stapes

PRINT the word next
to the image on the next slide.

book

table

bucket

What materials transmit sound?

Let’s start with solids.
Can sound travel through a solid?

shovel

Solids have a definite shape and size.

Wait. Wait!
Do you remember what a solid IS?

Locate

Transmitting Sound in a Solid

hammer

small nail

a length of string
about 6 feet or 2 meters

two recycled food cans or plastic cups

Use a nail
to make a small hole
in the bottom
of the cans or cups.

Insert the string
through each hole
and knot each end
of the string inside
the cans, as shown.

Make sure the
KNOTS are BIG.

This is a classic experiment for two people.

Making a Tin Can Telephone

Sound through solids?

Stretch out the string
the full length
between two people.

BE SURE the string
is TAUT.

One person speaks into one can or cup
while the other one places the second can over his/her ear.
Take turns speaking and listening. Do you feel the vibrations?

The string is a solid,
a physical medium.

Did sound travel through the string

Click for answer.

YES!
Definitely.
And you made
a tin can telephone
to prove it.
Congratulations!

The tin can telephone has
been known for centuries!

For a short time, these acoustic telephones actually competed
with the FIRST electrical telephones.

The maximum range of the tin can telephones was limited,
but hundreds of innovations
increased that range
to as far as 3 miles (4.8 km).

You can detect sounds faster through the solid ground
than through air.

Trackers and hunters
often press their ears
to the ground to better
hear the footsteps
of people or the
hoofbeats of animals.

Try it!

Can sound travel through a liquid? Test it!

Find these items:

Sound Through Liquids

plastic bag
or balloon

rubber band
or twist tie

This is an experiment for two people.

water

Does Sound Travel
Through Liquids?

Partially fill
the plastic bag
or balloon
with water.

Use the
rubber band
or twist tie
to seal in
the water.

The listener holds the bag of water over one ear and covers their other
ear with their free hand.

The speaker talks
through the bag.

Can you hear what is being said?

Click for answer.

Water is a liquid,
a physical medium.

Does sound travel through a liquid

YES!
Definitely.
Sound travels through a liquid.

Does sound travel through a gas?

The air you breathe is a gas.

What do you think?

HINT: When you speak,
do others hear you?

Then bang
two spoons
together
under water
in a bowl or sink.

Can you hear the sound in air.
Can you hear it when the sound
has to travel through water first?

Bang two spoons or
spoons and a pot together.

Try this:

First,
in the air.

YES!
When you speak and when you
bang the spoons together,
the sound is transmitted through
the gases in the air to your ears.

Click for answer.

Does sound travel through a gas

You have tested the transmission of sound
through the mediums of solids, liquids and gases.

What about a vacuum?
A vacuum is empty space,
the absence of any medium.

If you were in outer space
or standing on the Moon,
COULD you hear a sound
through the emptiness
of space which is
a near vacuum?

Scientists first tested whether sound
can travel in a vacuum by ringing
a bell in a vacuum chamber.

What IS a vacuum chamber?

It is an enclosure where almost
all of the air has been SUCKED
OUT using a vacuum pump.

A vacuum pump can SUCK AIR OUT through this tube.

In this famous bell jar experiment, scientists placed a bell inside an enclosed glass chamber.

The bell could be heard ringing inside the air filled chamber.

A vacuum pump was
then used to remove the air
from the chamber.

Did they still hear the bell ringing as air was removed?