Diving octopus
Lesson 2: Floating and Sinking
Brief description
Students make and manipulate a simple bottle diver to investigate its floating and
sinking properties. They can experiment with variables and make observations to .
They apply the same principle to make and keep a toy octopus which dives or floats
in a soft-drink bottle.
Duration:
Year Level:
Topics:
Preparation:
Extensions:
60 to 90 minutes
Middle to upper primary
Floating & sinking, Buoyancy, Density, Liquids & Gases
20 minutes
ART – Decorate the ‘octopus’s garden’
SCIENCE – Research submarines
SCIENCE – Research octopuses
LANGUAGE (CREATIVE WRITING) – write a story: set in a submarine / about
an octopus
Overview
Whole class
Teacher demonstration
Discuss procedure
Designate group work jobs
Small groups
Activity 1 – Investigate a simple bottle diver (30 – 45 min)
Activity 2 – Make octopuses
Discuss activities
(30 min)
Plan next science lesson
Whole class
Art Extension
(10 min)
Decorate soft-drink bottle
(optional)
Materials and equipment
Simple bottle diver investigation
Total Qty
30
Description
student worksheets
(1 per student)
5 pages - download separately and photocopy
6
plastic cups
(1 per group)
6
plastic buckets or tubs
(1 per group)
clear drinking straws
(2 per group)
12
note: air bubble needs to be visible when submerged in water
6
strips of Blu-Tac or U-Tac
(1 per group)
6
1 litre soft-drink bottles
(1 per group)
continued …
Lesson 2 – Diving Octopus
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© Ruben Meerman 2004
Diving octopus
OPTION 1: Pipe cleaner design
Qty
Description
30
coloured flexible drinking straws
(1 /student)
30
coloured pipe-cleaners *
(1 /student)
30
soft-drink bottle
(1 /student)
60
OPTIONAL:
(2 /student)
small stick-on eyes**
* available from art & craft suppliers – ensure there are sufficient quantities
of popular colours (white is unlikely to be popular for this activity!)
.
OPTION 2: Paper clip design
Qty
Description
30
flexible drinking straws
(1 /student)
30
small coloured paper clips
(1 /student)
6
strips of Blu-Tac or U-Tac
(1 /group)
coloured plastic shopping bags
(2 –3 /group)
OPTIONAL: small
(2 /student)
2–3
60
stick-on eyes
** use a suitable adhesive to attach eyes (teacher may have to perform
this step depending on age of students) / or use permanent marker
to draw eyes
Preparation
Materials for teacher to collect:
y Sufficient quantities of plastic cups, plastic buckets or tubs, Blu-Tak or U-Tac and
drinking straws (quantities required listed on previous page)
y Select the octopus design you will use and gather materials (quantities required
listed above)
y Download and photocopy 30 student worksheets
Materials for students to collect:
Ask students to collect the following materials from home until there are sufficient
quantities of each (extra materials can be saved for future lessons depending on available
storage space):
y empty 1 litre soft-drink bottles (minimum of 1 per student required for lesson)
y plastic grocery bags in various colours
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© Ruben Meerman 2004
Objectives
Accurately describing how the bottle diver works requires the correct synthesis of
several scientific concepts. This may take different amounts of time for individual
students due to prior knowledge. Asking questions about each concept in isolation
may help students overcome misconceptions leading to a correct explanation of the
diver’s operation.
Students’ prior knowledge
Students are familiar with their group work job responsibilities.
No prior knowledge is assumed for this lesson.
Science skills
Students will:
y follow the instructions to make a simple bottle diver
y manipulate the bottle to make the bottle diver sink and surface
y observe that the air bubble inside the straw is compressed when
the bottle is squeezed
y observe that the air bubble returns to its original size when the
bottle is released
y experiment with and identify variables which affect the operation
of the bottle diver
y describe the operation of the bottle diver
y demonstrate their understanding of the bottle diver by solving
problems
Science concepts
y
y
y
y
y
air (gas) is less dense than water (liquid)
objects which are less dense than water float
objects which are more dense than water sink
liquids are compressible fluids (they can be squashed)
gases are incompressible fluids (they can’t be squashed)
Describing the bottle diver:
y squeezing the bottle squashes forces water into the straw and
squashes the air bubble
y the extra water inside the straw reduces the buoyancy of the
straw diver causing it to sink
Positive attitudes
Students will:
Lesson 2 – Diving Octopus
abc.net.au/science
y work cooperatively in small groups
y ensuring each member has an opportunity to see and
manipulate the bottle diver
y use water sparingly and dispose responsibly (eg pour onto school
garden beds, not into sinks)
y handle equipment and materials responsibly
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© Ruben Meerman 2004
Procedure
Introduction (Whole class / 5 – 10 min)
y Introduce and discuss the bottle diver activity without describing how it works
y Allocate group work jobs
Teacher demonstration - OPTIONAL
y Demonstrating the bottle diver without revealing the method of operation first will get
students excited about experimenting with it – and if your bottle diver is only just buoyant,
students won’t notice you are squeezing the bottle
y You can pretend the diver sinks or floats depending on the pitch of your voice (talking in a
low pitch makes the diver sink, and higher pitch makes it rise) or by mind control
y If available, you can use a plastic tomato or soy sauce sachet and tell the class you
accidentally discovered this very strange phenomena at a restaurant (you don’t have to do
anything to these sachets – just put one in a bottle full of water and squeeze)
y You can reveal that you are actually squeezing the bottle but challenge your students to
describe how it works
Hands-on activities (Small groups / 30 – 45 min)
Small group activities
y All group members cooperate to prepare a Work Station by grouping desks
y All group members read the worksheet instructions
y Equipment Managers collect materials required from Science Store
y Group Supervisors ensure group adheres to instructions and completes activities
y Records Officers keep careful notes of results where necessary
y Equipment Managers clean and return equipment to the Science Store
y Remainder of group cleans Work Station and returns desks to normal locations
Early finishers
y Early finishers could begin decorating their ‘octopus’s garden’, research submarines
of octopuses on the internet (if available) or design games to play with their bottle
divers.
Conclusion (Whole class / 10 – 15 min)
Class discussion
y Lead a discussion about the activities by asking questions such as:
“was it difficult to figure out how the bottle diver works?”
“how do you think submarines surface and dive?”
“does anyone know any more amazing facts about octopuses?”
“has anyone ever seen giant octopuses or squid in the news?”
Plan next science lesson
y Ask students to collect and bring in any household items you might require for the
next lesson you have planned
Art extension: decorate and draw an underwater scene for your octopuses bottle
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© Ruben Meerman 2004
Teacher notes
Making straw bottle divers
Complete instructions including diagrams for making the straw diver are provided on the
student worksheet. Some extra notes and solutions to are provided to common problems
below.
Buoyancy testing
The diver needs to be only just buoyant.
Adjusting buoyancy is a simple matter of
adding or removing Blu-Tak but it is worth
emphasising why students should perform
their buoyancy tests carefully – they will be
eager to get the diver in the bottle and may
rush this step.
Remind them that it is much easier to retrieve
divers which sink from a plastic cup than a
bottle and to ensure that the water level is
deep enough for the diver to float. If the water
level in the cup is too low, the diver may be
resting on the bottom of the cup but appear
to be floating.
too buoyant
just buoyant
Solutions to common problems
Buoyancy is good but diver won’t work
Ensure the bottle is completely full and doesn’t have a large air bubble at the top
Water level may be too low in cup so diver appears to float but is resting on bottom
Retrieving a sunk diver from bottles
If a divers malfunctions and sinks in the bottle, seal the end of the bottle with your thumb
or palm and turn the bottle upside down. Release momentarily to let the diver fall into a
bucket and return the bottle to the upright position.
Other bottle diver designs
There are numerous ways to make a bottle diver
including:
y inverted glass test tubes
y eyedroppers with a ball bearing or nail as
ballast
y tied, uninflated balloon with paperclips as
ballast (pictured) or containing a marble or
pebble
y plastic tomato or soy sauce sachets
y biro lids with plasticine or Blu-Tak as ballast
Lesson 2 – Diving Octopus
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A sealed balloon diver with
paperclips as ballast
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© Ruben Meerman 2004
How it works
Although each of the concepts below are simple enough in isolation, correctly
synthesising them to describe how the diver operates requires complex thinking skills.
Each student will construct an explanation based on his or her prior knowledge resulting
in a variety of theories. As a result, you may find that students who have difficulty
explaining how the diver works are applying sound, but unrelated scientific concepts.
Asking questions about each of the concepts below may help students synthesise them
correctly.
Key concepts:
y air is a compressible fluid (ie it can be squashed)
y water is an incompressible fluid (ie it cannot be squashed)
y the air bubble inside the straw makes the diver buoyant
y squeezing reduces the volume of the bottle
you can prove this by squeezing a bottle full of water with the lid off
y when the sealed bottle is squeezed, water flows into the straw and the air bubble
is compressed (squashed)
y the buoyancy of the straw is reduced when the air bubble is squashed which
makes the diver sink
y when the bottle is not being squeezed, the air bubble in the straw expands back
to its original size and the diver surfaces
Variables:
y length of the straw (longer is more buoyant because of the larger air bubble)
y amount of eight added (weight reduces the buoyancy of the diver)
y amount of water in the bottle
operating the diver is easiest if the bottle is full to the brim
Sealed divers work too:
To demonstrate that the density of air increases when it is compressed, perform a
demonstration with a sealed bottle diver such as the balloon and paperclip diver on the
previous page. Tie a knot in an uninflated balloon and add some paperclips. Keep adding
paperclips till the balloon sinks, then remove one. This may help some students overcome
persistent misconceptions about how the diver works.
Application in submarines
Submarines have special chambers which can be filled with air or water to control
buoyancy. Air is pumped into or out of these chambers by compressors. If the chambers
are completely filled with air, the submarine is buoyant. If they are partially filled with air
(and water), the submarine can be made neutrally buoyant (ie remains at whatever depth
without requiring any propulsion). If the chambers contain more water than air, the
submarine will dive.
Further reading:
How Stuff Works
http://www.howstuffworks.com/submarine.htm
Lesson 2 – Diving Octopus
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© Ruben Meerman 2004
.
Investigating
Straw Submarines
Name ______________________________________
Materials required per group:
1 straw
1 bucket (empty)
1 small blob of Blu-Tak or U-Tac
1 pair of tweezers (optional)
1 plastic cup
1 pair of scissors
2 soft-drink bottles
(one full, one ¼ full of water)
Introduction
You are going to make a simple submarine which can dive and surface by squeezing the bottle.
You will investigate how it works by observing what happens inside the straw and bottle. If you
need to retrieve your diver from the bottle, work over the bucket to catch any spilling water.
Procedure
1. Prepare the submarine
Cut a length of straw approximately 7 cm long
Make a small, round flat disk with the Blu-Tak to seal the top
of the straw
Make a roughly cylindrical piece of Blu-Tak about 7 cm long
Wind the long blob around the outside of the other end of
the straw to act as a weight (it has to fit in
2. Test buoyancy and launch
Float the submarine in a cup of water – it should only just
float
If the top of the straw is more than 5 mm above the surface,
add a little more Blu-Tak to the bottom
If the straw sinks, remove a little more Blu-Tak from the
bottom
Make sure your soft-drink bottle is completely full of water
Gently drop the straw into the bottle and put the lid on –
you’re ready to operate the submarine
Too buoyant
Just right
Squeeze to dive
Release to surface
3. Investigate the submarine
Make the submarine sink by squeezing the bottle and stop
squeezing to make it surface by
(If nothing is happening, your submarine is still too buoyant)
Repeat several times until you think you can explain how the
submarine works – here are some things to consider:
What is in the bottle? What is in the straw?
Would the submarine work if the bottle was not
completely full of water? You can try this if you’re not
sure.
What happens if you squeeze a full bottle of water
without the lid on?
/ continued on other side …
Straw Submarines – Student Worksheet
ABC Science Online ( abc.net.au/science )
Page 1
© Ruben Meerman 2004
Describing
Straw Submarines
Observations
Draw a picture of what you saw in the boxes provided
SQUEEZING THE BOTTLE
Draw the straw and what the air bubble inside
looks like when you are squeezing the bottle:
NOT SQUEEZING THE BOTTLE
Draw the straw and what the air bubble inside
looks like when you are squeezing the bottle:
Explanation
Can you explain how the straw submarine works in words?
_____________________________________________
_____________________________________________
_____________________________________________
_____________________________________________
Challenge questions
1. If you didn’t have any more Blu-Tak or any other type of weight to add to it, how could you
make your submarine LESS BUOYANT ? Write down as many ideas as you can
_____________________________________________
_____________________________________________
_____________________________________________
_____________________________________________
2. Why is it harder to make the submarine work when the bottle is not completely full of water?
_____________________________________________
_____________________________________________
_____________________________________________
_____________________________________________
Straw Submarines – Student Worksheet
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© Ruben Meerman 2004
Make your own pet
Diving Octopus
The Diving Octopus works in exactly the same way as your Straw Submarine. Two ways to make
your own Diving Octopus are provided here. Pick the one you have all the materials for.
Diving Octopus – Paperclip Design
Materials required:
1 bendable straw
1 small blob of Blu-Tak or U-Tac
1 soft-drink bottle
1 plastic cup (to test buoyancy)
1 piece of coloured plastic bag
1 pair of stick-on eyes (optional)
Instructions:
Step 1 – Cut Straw
Step 4 – Attach arms to body
Bend the straw and cut it so that there are two
legs approximately 2 cm long.
Slide the one end of the paper clip into each leg of the
body so they stay firmly in place
2 cm
Step 2 – Make the arms (not tentacles)
Step 5 – Attach Blu-Tak and do buoyancy test
Find out why they’re called arms on page 5.
Cut a rectangular piece of plastic about 3cm
wide and 5 cm long. Carefully make 7 cuts so
so that you end up with eight arms
Attach a small blob of Blu-Tak and test the buoyancy
of your octopus in a plastic cup. If the head floats
more than 5 mm above the water, add more Blu-Tak.
If it sinks, remove some Blu-Tak.
5 cm
You can draw or stick on some eyes to give you
octopus a bit of personality or attitude before
putting it into your soft-drink bottle.
3 cm
Step 3 – Attach arms to paperclip
Bend the paper so it is slightly open and
carefully thread the arms on like this
Remember: fill your bottle to the top to make diving and
Surfacing easy
Straw Submarines – Student Worksheet
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© Ruben Meerman 2004
Make your own pet
Diving Octopus
Diving Octopus – Pipe-cleaner design
Materials required:
1 bendable straw
1 long pipe-cleaner
1 pair of stick-on eyes (optional)
1 plastic cup (to test buoyancy)
1 soft-drink bottle
Instructions:
Step 1 – Cut Straw
Bend the straw and cut it so that there
are two legs approximately 2 cm long.
2 cm
Step 2 – Bend pipe cleaner to make arms
Use these pictures are a guide to making
arms for your octopus. You’ll notice that this
design only has four arms, but the end result
looks enough like an octopus to get away
with.
You can make the arms any way you like but
you need to double over the ends of the
pipe-cleaner so they stay firmly attached
inside the straw.
Step 3 – Buoyancy test
When you have finished making the arms,
attach them to the body. Test the buoyancy
of your octopus in a plastic cup.
If the head floats more than 5 mm above the
water, your octopus is a too buoyant. There
are two ways you can make your less
buoyant.
1. Cut a small piece from the ends of the
straw
2. Squeeze a bit of air out of the body –
squeeze gently and you will see an air
bubble escape.
One way to make four tentacles
If your octopus sinks, get a new straw and
make the legs on the straw slightly longer.
Step 4 – Add eyes (optional)
When you are sure your octopus has the right
Buoyancy, draw or stick on some eyes. Then
carefully put your octopus in a soft-drink bottle
full of water.
Straw Submarines – Student Worksheet
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Page 4
© Ruben Meerman 2004
Decorate your
Octopus’s Garden
You can decorate your octopus’s garden with anything you like.
Below is a list of just a few things you could use.
Be creative and give your octopus a happy home!
Suggestions for decorating your Octopus’s Garden:
Sand, pebbles, shells, aquarium decorations
Add a tiny bit of blue food colouring to the water
Make ‘seaweed’: weight strips of plastic with a paperclip,
and attach something that floats on the other (eg a piece of
styrofoam).
Sprinkle glitter into the water. Shake the bottle gently if the
glitter settles.
Note: choose items that will fit through the neck of the bottle and
don’t use anything that might dissolve, decompose or deteriorate
in water.
Draw an underwater scene and attach it to your
bottle:
Draw and colour in an underwater scene on white paper.
When you are happy with it, wrap it around the bottle and
secure it with some sticky tape.
Amazing octopus facts
Octopuses are amazing animals with eight arms and no bones. They are part of a group of animals
called molluscs which generally have shells. Octopuses, along with squid and cuttlefish, belong to a
class of molluscs called cephalopods. Cephalopods don’t have external shells. Cuttlefish and squid
have small interna shells and octopuses don’t have one at all. Here are just a few amazing facts:
Arms ,
not tentacles
Not many people know this but octopuses have eight arms. Squid and cuttlefish also
have eight arms plus two tentacles. Tentacles are longer and usually only have suckers
at the tips. Even some dictionaries get this wrong and say squid have ten tentacles!
Blue blood
Humans (and most other animals) have red blood it contains iron which carries oxygen
to our cells. Cephalopods use copper instead, which makes their blood blue.
Three hearts
Octopuses separate hearts to pump blood through each gill. A third heart pumps it
blood the gills to the rest of the body
Intelligent
Octopuses have the most complex brain of all animals without back-bones
(invertebrates). The can solve problems and have short and long term memory so they
can solve similar problems the same way in future.
Jet propulsion
Octopuses, squid and cuttlefish suck in water and squirt it out to propel themselves.
Colours and ink
Octopuses can change colour to camouflage themselves by filling or emptying special
cells with pigments. If things get too scary, they squirt dark ink, turn white and jet away.
Short life
Most octopuses only live for one year, reproduce once, and die. Sounds so short and sad
to us, but it’s just a normal life for an octopus.
It’s octopuses!
The correct plural of octopus is octopuses, not octopi, though some seriously pedantic
people might argue and say it should be octopodes … confused? Just say octopuses.
Find out more about octopuses:
http://www.cephbase.utmb.edu/ (CephBase, short for Cephalopod Database, packed with great scientific info):
http://www.marinelab.sarasota.fl.us/OCTOPI.HTM (info at the famous MOTE Marine Labs in Florida)
Straw Submarines – Student Worksheet
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© Ruben Meerman 2004