1. Everyday examples of ‘pressure’
In this unit we start with aspects of science that are relevant in the home, and move on to consider issues of wider importance to society. Sometimes the everyday applications for the topic you are studying are obvious, but sometimes they are not. If you ask an individual about how ideas about pressure manifest themselves in their lives, they probably would not come up with very much. But once they have the opportunity to talk in a group, you will find that the ideas will flow. Resource 2 provides guidelines for conducting a brainstorming session in a large group; Resource 3 provides lots of examples so that you can keep the discussion going. This approach would work with any physics topic that you have to cover.
Case study 1: Demonstrating pressure
Mrs Joyce walks into her classroom wearing her stiletto heels, carrying a wooden block with sharp nails stuck to it, a bottle of soda and a drinking straw, a blunt and sharp knife and two pieces of cake. She asked one of the students to walk with her outside the class on wet soft ground. She then asked the rest of the class to observe what happened to her shoes and those of the student. The students were keen to observe. She asked the students to support their observations scientifically.
Mrs Joyce had noted that the boys liked soda. She promised them that she would give the soda to any who would stand on the block with nails. The boys were not willing. Why did they decline? She asked them to give a reason. What is the best way to walk on nails? Hari commented that he had seen someone lying on a bed of nails at a circus.
Next Mrs Joyce asked two boys to compete at cutting the two pieces of cake; one using the sharp knife and the other using the blunt one. She wanted them to see which would produce the cleanest cut. She noted that the boys knew the winner before the competition started. How did they know the winner? Using the definition of pressure which the boys had learnt earlier they were able to give an explanation of each of the events.
Activity 1: Demonstrating everyday pressure
Gather your class round the front. Fill a cup up to the brim with water. Make sure the water is almost overflowing. Slide a piece of cardboard across the top. Holding on to the card, turn the cup of water upside down. The water will stay in the cup – make sure you practice before the lesson, or it could be messy! The card stays in place because of the air pressure. The pressure from the air is greater than the weight of the water. Ask questions to try and get your students to come up with an explanation.
Get your students to work in pairs to explain:
- how a straw works
- how a suction pad works
- why elephants and camels have large feet
- why it is possible to lie on a bed of nails.
Choose four pairs to report back.
Finish off with a brainstorm in which you encourage the class to think of other everyday examples of pressure.