3 Helping your students to achieve a better understanding of energy and work
When a student has a misunderstanding that seems to explain an idea, they will only give it up if you can show them that another way of explaining the idea works better. Sometimes students will partially accept the ‘new, improved’ model, but create another ‘hybrid’ model of their own, or may switch between models depending on the situation.
There is no single solution to the problem, but research and common experience suggest that the following strategies help:
- Give students opportunities to discuss their ideas with other students in a supportive environment.
- Ask students to use their model to predict what will happen in different situations, and identify situations where their current model does not work but an accepted scientific model does. Discuss the differences between these models.
- Continue to present opportunities for students to challenge and refine their ideas.
Carefully structured practical experiences and demonstrations can be an effective way of providing evidence to challenge a misunderstanding. They don’t have to be big, spectacular experiments with lots of equipment: sometimes quick, low-key demonstrations and practical experiences can provide what is needed. Whatever you do, the important points to remember are that:
- the practical experience is there to support the development of ideas, so you must be clear about what you will need to draw their attention to
- you check the practical experience beforehand exactly as you intend it to be done, to make sure that students will be able to experience what you intend them to experience.
Activity 3: Learning about energy
This activity will help you to develop your in-class practice by using a practical activity with focused questioning to direct your students’ attention. (This demonstration is based on Activity 11.6 in the Class IX textbook and is one of several related to kinetic energy.) The purpose of the demonstration is to emphasise that energy is not ‘used up’, just converted from one form into another.
Drop a ball from an increasing height into a tray of wet sand. Start at a height of 25 cm and repeat from heights of 50 cm, 1 m and 1.5 m. Your students should notice that dropping the ball from an increasing height results in deeper impact craters.
You might use the following sequence of questions, or similar. The point of the questioning is to track the energy. The questions are in bold and the responses are in plain text.
- Which needs most energy to make it – a deep crater or a shallow one? Why?Students should say the deep crater, and may say that digging a deep hole takes more work than digging a shallow one.
- What provided the energy in this case? The ball. The ball’s energy is transferred to the sand.
- Is the ball doing work on the sand, then? Explain. Yes, because it is making the sand move.
- What does the crater depth tell you about the energy supplied by the ball when dropped from an increasing height? The ball supplies more energy to the sand when it has been dropped from a greater height.
- So, which ball had most energy as it hit the sand? The one that made the deepest crater.
- So, which ball must have had most energy before it was dropped? The one that was dropped from the greatest height.
- So, what can you say about the energy of the ball when it has landed in the sand? The energy has been transferred to the sand. (This is the key point for making the connection. Some students may say it has ‘gone’. If they do, ask them where it has gone.)
Now you need to pull all of this together by asking students to give a description of the whole sequence, not just piece by piece:
- To recap, tell me about the ball’s energy from when it is raised, then as it drops, then as it lands: what can you tell me about the amount of energy it has?The ball gains more (potential) energy the higher it is lifted. As it falls, the ball gets faster – so we can say it has more kinetic energy the faster it falls, but it doesn’t have more energy overall (because it has less potential energy). When the ball has landed in the sand, it has lost all the energy you gave to it by lifting it up; it must have lost all the kinetic energy it had just before it hit the sand, because we can see it has stopped.
- Where did all that the energy go? It was transferred to the sand to move it. Or, to put it another way: it was used to do work on the sand.
If you have a very large class, you could do the demonstration to smaller groups, while the rest get on with some work from the textbook. By planning the questions carefully in advance, you will be able to make good use of the demonstration. Of course, they might not respond as you expect, but if you are clear about the purpose of the demonstration, it will be easier for you to react to what they say.
Careful questioning is a very good way to find out what your students are thinking. To find out more about using questioning in your classroom read Resource 4.
2 Finding out about your students’ understanding of work and energy