This lesson will allow students to investigate and compare the stain resistant (moisture repellent) capacity of wool compared with cotton and draw conclusions about the suitability of these textiles for a range of everyday uses.
Students will have the opportunity to:
- test the stain resistant capacities of wool compared with cotton
- consider the implications of wool’s ability to repel water in a range of everyday uses.
Setting the context
While the core of the wool fibre can absorb up to a third of its dry weight in moisture, the surface of the fibre has a waxy coating that repels liquids. This surface layer is not easily removed by washing or processing. Water droplets on the surface of wool clothing will bead and roll off instead of being absorbed into the fabric, as occurs with cotton, allowing it to resist many common everyday stains.
The focus of this lesson is to encourage students to think about the link between the properties of a fibre and the implications for its end use.
Review the class science journal and discuss the observations students have made so far about wool including the physical features that help wool protect sheep under arrange of weather conditions and the features we can’t see or feel such as fire resistance.
Explain to students that wool has some other unique features that we can’t see, but we can test for, such as water repellence and stain resistance. Ask students why this property might be useful. Encourage discussion with questions such as: “Has an ice-block ever dripped while you were eating it?” “What happened?”, “Have you ever trodden in water when you were wearing socks?” “What happened to your feet?”.
Body of lesson
- Distribute the student worksheet Resist that stain to students and explain that you will be asking them to predict what will happen when you drop coloured water onto the cotton socks and wool socks. They will need to record their predictions before and after they have observed the demonstration.
- Lay each of the socks on some newspaper or a tea towel on the table and tell students that you will place a droplet of coloured water on each sock and ask them to observe what happens to the water.
- Ask students to predict what will happen when the water is placed on the sock and get them to circle the corresponding option on their worksheet.
- Using the eye dropper, draw up water from the jug and slowly place a droplet on the cotton sock. The sock will absorb the water immediately. Repeat the process with the wool sock. The droplet of water will sit on the surface of the wool sock and not be absorbed. You can then use the cotton sock to absorb the water droplet from the wool sock.
- Ask a student to come forward and feel both socks and describe how they feel. The wool sock will still feel dry, while the cotton sock will be wet where it has absorbed the water.
- Ask students to describe what happened during the demonstration. Discuss whether what happened matched their predictions. Ask students to record what happened on their worksheet by drawing what they observed.
- Organise students into small groups of three or four students and allow them to replicate the activity in their groups.
- As you go around each group as students to describe again what is happening. Encourage them to think about what might happen if they split a drink while wearing a wool T-shirt, what would happen if they were wearing a cotton t-shirt? Encourage students to think about other items of clothing that might be made of cotton or wool, such as jumpers and hoodies (sweaters). Ask students to imagine what might happen if they were wearing these clothes on a bushwalk in foggy or misty weather.
NOTE: Wool is the preferred fibre for many outdoor activities for its water repellant qualities as well as its ability wick sweat away from the skin and help regulate body temperature.
Ask students to help you develop a sentence to describe the water and stain-repellant properties of wool and include this in your class journal
Explain that during then next lesson you will be considering how the properties you have been investigating influence the way we used wool in a range of everyday products.
Links to the Australian curriculum:
- Science involves exploring and observing the world using the senses (ACSHE013).
- Respond to questions about familiar objects and events (ACSIS014).
- Explore and make observations by using the senses (ACSIS011).
- Share observations and ideas (ACSIS012).
- Engage in discussions about observations and use methods such as drawing to represent ideas (ACSIS233).