TEMPERATURE AND WATER DENSITY
Curriculum Level
4/5
Strand
Physical World, Physical inquiry and physics concepts
Achievement Objectives
Students will:
Level 4
Explore, describe, and represent patterns and trends for everyday
examples of physical phenomena, such as light, sound, waves and heat
Level 5
Identify and describe the patterns associated with physical
phenomena found in simple everyday situations involving light, sound,
waves, and heat.
Nature of Science, Investigating in science
Develop and carry out more complex investigations, including using
models.
Specific Learning Outcomes
The students should be able to:
 Explain the density of water as it relates to temperature
 Identify the forces governing convection in liquids
Teacher Instructions
This activity involves a teacher demonstration and a student practical; preparation is required.
Day before class
Cut two 2L plastic drink bottles to be about 20cm tall. Drill or punch two holes one above another
and just large enough for the straws to fit into snugly; one hole about 5cm from the bottom and the
other about 15cm from the bottom. Fit the straws into the holes horizontally to join the two bottles
at the 5cm and 15cm levels. Use the glue gun to secure the straws into the bottle openings to make
them leak proof.
Mix dark blue food colouring into water, pour into ice cube trays and freeze
At start of demonstration
Boil about 2L of water and chill another 2L with ice. Place one of the 2L bottles in a bowl and
surround with ice.
Add red food colouring to the hot water and green to the chilled water. Pour the hot water into one
2L bottle, and add cold water into the iced 2L bottle.
Students observe the cold green water travel through the lower straw, while the hot water travels
through the upper straw. Have patience and each bottle will have a distinct layer of hot red water on
top, and a cooler green layer of water on the bottom.
Student group practical
1
Adapted from a resource developed for Te Hiringa i te Mahara (THM), a project funded by
the Ministry of Education and managed by Gardiner Parata Ltd (GPL). THM is a trademark of GPL.
© New Zealand Ministry of Education 2009 – copying restricted to use by New Zealand education sector.
Students will place a shallow long glass dish of warm water onto grid paper that has been marked in
centimetre intervals. One coloured ice cube will be placed iat each end of the dish and the movement
of the coloured water observed, recording the distance travelled at two minute time intervals.
Student Instructions
After watching the demonstration by your teacher, follow the instructions on the sheet provided to
carry out your own activity.
Resource Requirements
 2x 2L plastic drink bottles
 2x plastic straws
 Glue gun and glue sticks
 Hot plate
 Green. blue and red food colouring
 Crushed ice
 Craft knife
 Bowl
 Shallow clear dish – one per group
 Ice cubes of coloured water – two per group
 Grid/graph paper with centimetre intervals measured and marked along the length – one per
group
 Globe of the Earth
2
Adapted from a resource developed for Te Hiringa i te Mahara (THM), a project funded by
the Ministry of Education and managed by Gardiner Parata Ltd (GPL). THM is a trademark of GPL.
© New Zealand Ministry of Education 2009 – copying restricted to use by New Zealand education sector.
Student Group Activity
Dividing the Water
You have just seen that warm and cold water can actually separate: the cold water sinks and the
hotter water rises to the top. Also, you will have seen that the water will move when a temperature
difference exists. You are going to do your own demonstration in groups to show water moving
because of temperature differences as it does forming ocean currents.
Use a globe to identify that all the oceans are interconnected into a ‘world ocean’. Decide where the
water would be warmer – near the equator or near the poles.
Carry out an experiment to demonstrate how the colder waters nearer the poles and the warmer
waters nearer the equator mix together and move to create ocean currents:
1. Fill a clear flat dish with warm tap water to represent the warm water near the equator and
place it on top of a piece of grid or graph paper that has a line marked into 1 cm intervals
drawn along its length.
2. Now place one coloured ice cube at each end of the dish representing the cold water near the
poles. Start your stopwatch, and be ready to observe results at 2 minute intervals.
3. Predict what will happen as the ice melts.
4. Record the results of your experiment.
5. Draw labelled diagrams and an explanation of how differences in water temperature in
different parts of the “world ocean” cause ocean currents.
Throughout human history, ocean currents have been vital in such diverse activities as planetary
exploration, rubbish dispersal, and the spreading of ocean seeds. From ancestral waka travelling to
Aotearoa to ocean-spilled oil polluting shorelines, ocean currents have played a part in taking
adventurers, toxins, and sea beans all over the planet.
Warmer water from the oceans around the equator rises to the top, while colder water from the
oceans around the poles sinks to the bottom. Ocean currents are caused by the rising and sinking of
warmer and colder water.
.
Reference Material
Students will observe that the cold (coloured) water sinks and moves along the bottom of the baking
dish toward the warmer water in the middle; the warmer water moves toward the ends of the baking
dish; as the cold water begins to warm, it begins to rise.
3
Adapted from a resource developed for Te Hiringa i te Mahara (THM), a project funded by
the Ministry of Education and managed by Gardiner Parata Ltd (GPL). THM is a trademark of GPL.
© New Zealand Ministry of Education 2009 – copying restricted to use by New Zealand education sector.
Assessment Task
None.
Marking Schedule
None.
4
Adapted from a resource developed for Te Hiringa i te Mahara (THM), a project funded by
the Ministry of Education and managed by Gardiner Parata Ltd (GPL). THM is a trademark of GPL.
© New Zealand Ministry of Education 2009 – copying restricted to use by New Zealand education sector.