2 Finding out about your students’ understanding of work and energy

How can you find out about your students’ understanding of work and energy? If they are able to get all the right answers for calculation questions, you might assume that they have good understanding. However, students can hold misunderstandings about work and energy but carry out calculations correctly. The rules they have applied to carry out the calculation do not rely on understanding of the underlying physics.

For example, suppose you ask a student to calculate the potential energy gained by raising an object of mass m through a height h. They know that Ep = mgh, so if you give them values for m, g and h they can do the calculation. However, they may be unable to explain what happens when the load is released and falls to the ground in terms of energy transfer and energy conservation.

They may say that the load had potential energy when raised, that it had kinetic energy when it was falling, and that when the load landed its energy had somehow ‘gone’. It may take some further questioning to find out what might have happened to this ‘missing energy’ if energy is conserved.

There are some simple strategies that you can use to probe your students’ understanding of work and energy. What all these strategies have in common is that they encourage students to share their ideas with you and with other students. This is very important, as existing knowledge and understanding act as foundations for new learning.

Useful strategies to find out about students’ understanding include focused questioning, group discussion and poster presentations, as well as the following approaches, which may be less familiar:

  • ‘Predict and explain’: Give students a situation and ask them to predict what will happen next and explain their prediction.
  • ‘True/false/unsure’ card sort: Give each pair or group of students a set of cards, each of which has a single statement about energy and work. Students sort the cards into separate piles for ‘true’, ‘false’ and ‘unsure’.
  • ‘Traffic lights’: Each group of students shows their decision about a statement by holding up a green (true), red (false) or yellow (unsure) voting card
  • Concept cartoons: Cartoons that show a situation with two or three statements about what is happening. Students have to decide which statement(s) they agree or disagree with, and say why.
  • Annotated diagrams: Ask students to annotate an image or diagram of a system or a situation, using ideas about energy and work

You can find examples for each of these in Resource 2.

Case Study 2: Showing understanding in a classroom activity

Miss Bulsara tries out some strategies for probing her students’ understanding of work and energy.

Whenever I have taught work and energy to my Class IX, they always seem to manage to do the calculations, but often seem to make mistakes in questions where they have to describe or explain something. Perhaps if I knew what my students found confusing, I could help them!

This year, I decided to try to find out more about what my Class IX students don’t understand about work and energy. I didn’t want anyone to spend a lot of time on drawing or writing things out neatly, so I decided to use two of the concept cartoons we had been shown at a training session. [These are the cartoons in Resource 2.] Students like hearing someone else’s opinion and making a judgement about it, and I like the idea of using concept cartoons, because they encourage students to consider different possibilities before they answer.

First of all, I divided my students into groups of three or four students, and gave each group the two concept cartoons. I told them that they had five minutes to discuss each of the two cartoons in their group and decide what the best answer in each case was. I gave each group two decision cards, one with a large A on it (for ‘answer A is better’) and one with a large B on it.

I walked round the classroom and listened to the discussions. Sometimes they were quite lively, but I could tell that my students were interested in the discussion.

I stopped the discussions after ten minutes and told my students to choose one person from each group to report on their decisions. I stood at the front of the room with everyone facing me, and asked the group representatives to show me their chosen decision cards at the same time, so I would be the only one who could see what all the decisions were. Not every group had agreed with what I thought was the best answer, but the other groups didn’t know that.

I asked someone from one of the groups that had chosen what I thought was the best answer to explain how they had decided. I wanted to encourage them to share ideas with the whole class without being embarrassed, so I praised the way they had offered the explanation, and said that when I was walking round, I’d been impressed by the discussions going on in all of the groups. When all the groups had voted on the second cartoon, I asked someone from another group to explain how they had made their decision, again making sure they had chosen what I thought was the best answer. My students wanted to know what I thought was the best answer and why, so we spent another five minutes talking about the cartoons.

Listening to my students helped me to plan my next lesson with them. Now I know much more about their existing understanding I can set up situations to introduce them to accepted scientific concepts.

Activity 2: Testing students’ knowledge of ‘work’ in class

This activity will help you to develop your in-class practice. You are going to use one of the strategies described in Resource 2 to look at your students’ understanding of work and energy. (This activity is based on Activities 11.2 and 11.3 in the Class IX textbook (the National Council of Education and Training version).)

  • Ask your students to think of situations from their daily lives that involve ‘work’. In each case, ask them to say how work is being done, and explain why they think that. You can treat this as an example of the ‘predict and explain’ approach. (Before the lesson, identify three or four examples of situations that you would like groups to consider. Make a note to yourself of what decision you would like and what you would like them to include in their explanation. Resource 3 will be helpful for this.)
  • Ask them to think about a situation in which an object is not displaced, even though a force acts on it.
  • Ask them to think about a situation in which an object gets displaced in the absence of a force acting on it.
  • Circulate as the groups discuss the different situations. Unobtrusively, make a note of what predictions each group makes and what reasons they give.
  • Discuss the answers that you hoped for with your students, explaining the reason for each prediction.
  • After the lesson, think about these questions:
    1. What were the most difficult situations for students to decide about?
    2. Which situations did most groups get right in terms of the prediction and the explanation?
    3. Which situations did most groups get wrong? What kinds of reasons were the groups giving in these situations?

Pause for thought

  • Were you surprised by any of the answers the groups gave?
  • Were there any common misunderstandings in your students’ incorrect explanations?
Figure 2 While your students are working, walk round and listen carefully to what they are talking about. If necessary, prompt them with questions, but don’t be tempted to tell them the answers.

1 Some common misunderstandings about energy

3 Helping your students to achieve a better understanding of energy and work