3. Setting open-ended tasks
In order to learn to solve problems, students need to be provided with open-ended activities that have a number of solutions. In order to develop their ability to solve problems you can be selective in the information that you give them. A good problem solver knows which questions to ask. For example, you tell them at the beginning of the topic that you want them to explain why a large ship can float in water. Don’t ask for the answer until the end, but make sure you give them some clues while you are teaching the topic. In Activity 3, you will set your students the task of changing the shape of a piece of Plasticine (or equivalent) to make it float. Once they have solved the problem, they should look at each other’s solutions and should be prompted to explain their own thinking (Resource 5 provides a writing frame that you could use). Resource 6 describes an alternative problem that you could set and suggests how it could be adapted for students of different abilities.
Case study 3: Solving a problem
Miss Chitsulo set up a competition: ‘Which “boat” can hold the most paperclips?’ and gave each group a piece of Plasticine: all the pieces were exactly the same size. Every group tried out their idea and then the class gathered round the winner and worked out why it had won.
Some students commented on how the boats got lower in the water as more paperclips were added. Miss Chitsulo asked the students to predict what would happen if you put the boat into very salty water (or into oil) and to explain why they thought that. She had some salt water and oil ready for them to try their boats out. She knew that this would provide an opportunity to think about what is providing the upthrust and allow students to explore some ideas about forces, and maybe use some things they already knew about the way ships float higher when unloaded and when in salt water rather than in fresh water. After the students had tried the winning boat in different liquids, she showed them some photos of plimsoll lines on ships (lines marked on ships to indicate the depth to which a vessel may be immersed in water) and they talked about how this helps keep ships safely loaded.
Activity 3: Investigating floating and sinking
You will need a bowl of water and some objects of different sizes, shapes and materials. For each of the objects, get the class to predict whether it will sink or float. If possible, it would be good to have a small piece of a hard wood that sinks and a large piece of a soft wood that floats. Encourage the students to explain their predictions before you test them. When they try to explain their thinking, they might get a bit confused, but it will help them to learn. Think back to your own time at college – the things we understand best are often the ones which confuse us for a while! Demonstrate that a lump of Plasticine (modelling clay) sinks when you drop it into a bowl of water. Challenge the class to devise a way to make it float, and if it can do that, to carry a small load. At the end, explain why an object floats, in terms of the forces. Ask students why an ocean liner made of steel can float.