KEEPING FOOD COOL
Description of activity
Students research, design and build a cooling system that can be used without electricity.
This activity will take 2 to 3 hours:
- research and gather resources
- build and evaluate.
Students may have studied how early settlers used cooling systems for food or the way in which third world countries, where electricity is limited, extend the shelf life of food.
They will explore the cooling effects of evaporation to help design a cooling system.
Knowledge and understanding
Various items depending on how students wish to build cooling system. For example:
- Clay/terracotta pots, sand, water containers, old towel, spade, straw/hay, recycled container to put food in, large pieces of old material, newspaper
- Access to water, thermometers, methylated spirits, fan
Work, health and safety
- Check relevant Work, health and safety guidelines.
- Highlight to students the need to be responsible and safe when using water.
- Be mindful of water spillage and slippery floors.
Evidence of work for assessment purposes
- Written account describing the effects of evaporation on temperature
- Annotated design plan of a cooling system
- Photos of the cooling system
- Description and results of the fair test carried out to determine the effectiveness of the cooling system
STEM teaching and learning activities
- Students discuss the following questions:
- What are some ways to help us keep cool?
- How do our bodies cool down when we get hot?
- Why do you think our bodies react that way to being hot?
- Discuss the question:
- How did people keep food cool before refrigerators?
- Students investigate the effects of evaporation by carrying out a primary investigation. For example:
- measure the air temperature
- dip a thermometer into methylated spirits, remove it and observe the temperature readings over a few minutes
- record the data in a table
- construct a line graph of this data.
- What conclusions can be drawn from the effect of evaporation on cooling?
- Students research different structures used to keep food cool.
- Students, in groups, design and build a cooling system to cool food or keep food cool. See Managing a process of design and Carrying out a design plan for assistance.
- Students devise a fair test to gather data on the effectiveness of their design.
- Students conduct their planned experiment, observe and record results.
- Students discuss their findings as a whole class.
Energy efficiency – using less energy to perform the same function
Evaporation – occurs when particles at the surface of a liquid, being hit by air particles, are moved into the gaseous phase
Evaporative cooling – a system or process in which:
- heat is removed from an object by the evaporation of a liquid
- air is cooled before passing through a space
Fair test – where only one factor is changed and all other factors are kept the same
- Independent variable – the factor that is changed during the investigation
- Dependent variable – the factor, affected by the change, which is measured or observed
- Controlled variables –other factors in an investigation that are to be kept constant
Renewable energy – energy collected from sources that can be naturally replenished, eg solar, wind, geothermal, biomass, ocean and hydro (water)
Key inquiry questions
Fair testing is the basis of the scientific process. The ability to design, plan and test a hypothesis or solve a problem is integral to all studies in science and technology.
How will you choose the experimental variables?
Experiments are done in order to find cause and effect relationships. In other words, experiments are designed to test whether a change in one factor causes something else to change in a predictable way. These changing quantities are called ‘variables’. There are three types of variables:
- Independent: the factor (only one) that you choose to change in order to see whether that change has an effect
- Dependent: the factor that allows you to see whether the change has had a measurable effect
- Controlled: there would generally be several factors that must remain constant. These constant conditions help ensure that it is only the independent variable that causes any change. The maintenance of controlled variables makes an experiment a ‘fair test’.
What makes this a fair test?
In order to compare the results of one trial with another, the only factor that should be changed is the one being tested, ie the independent variable. The more variables that are controlled effectively, the more likely it is that any observed change is caused by the changes in the independent variable, and not something else.
How much data will you collect?
In any collection of experimental data it is important to take a number of readings/do a number of trials, and then take the average of these readings. This reduces the effect of a ‘fluke’ result and thus increases the reliability of the data. Sometimes this can be achieved by having every group follow exactly the same method and then combining results. By allocating roles to group members and swapping the roles so that each group member does each task at least once, a number of trials are performed and results can be combined.
The following statement outlines some common preconceived ideas that many students hold, which are scientifically inaccurate and may impede student understanding.
Evaporation only happens with boiling water
Many students in Stage 3 will think of matter as consisting of particles. When they explain evaporation, students will often think of boiling water. They understand that heating water provides the particles with enough energy to ‘break away’ from the body of water to turn into water vapour. When the particles lose energy they re-form water droplets and condensation occurs.
Evaporation also occurs when there is no heating, for example when a puddle of water dries up. This happens because the particles of water, at the surface of the water, move from an area of high concentration of water particles, to an area of lower concentration, in the air. The rate of evaporation increases if the wind is blowing. The wind moves water particles away from the air above the water, thus increasing the movement of other water particles at the surface. Evaporation, the movement of water particles from the surface of water, also takes heat energy away from the body of water. This transfer of energy results in cooling on the surface of the water. When we get hot, we start to sweat. The evaporation of sweat from our skin helps us cool down, due to the transfer of heat energy from us to the moving water particles.
How to cool food without a fridge: Methods and inventions
How to build a Coolgardie safe: A simple design
What is this? Meat safe: How the meat safe was used
YouTube video: Fair test investigation clear introduction to fair testing
YouTube video: Scientific variables
Adjustments for the diversity of learners
This activity could be used with History Stage 3 learning about The Australian Colonies in considering how the early settlers may have used a cooling system for food. HT3-2
Geography Stage 3 studies regarding the protection of environments and investigating sustainable practices that protect our environment. GE3-2
Students explore the effects of temperature or humidity or air flow on evaporation. They:
- record the data in a table
- compare the two sets of data
- draw conclusions supported by the gathered data.
In this STEM activity, your students explored the idea of evaporation and its practical applications. This concept is further developed in Science Stages 4 and 5 and forms essential understanding in all disciplines of science.
Students will have designed and carried out an investigation. Recording the results has provided practice in accurate measurement, making tables and recording data. Proficiency in these skills is vital for your students to analyse information and become critical thinkers.