Diving octopus - ABC

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 abc.net.au/science

Page 1 © 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

Lesson 2 – Diving Octopus abc.net.au/science


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:


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


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 Lesson 2 – Diving Octopus abc.net.au/science


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


A sealed balloon diver with paperclips as ballast


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



.

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 )


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 ABC Science Online ( abc.net.au/science )


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



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.



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)



Diving octopus - ABC

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