2 Using an investigative approach in practical work on gravitation

Using an investigative approach can help your students to learn about the way in which scientists work. It will encourage them to ask questions and think about how they will test ideas. They also have to think about what they might expect to happen and why, and compare their results to their predictions.

Science teachers use investigations for a range of purposes, and different teachers will do investigations in different ways. There is no ‘right’ way to carry out investigations. You need to decide on the purpose and plan the activity to deliver the outcomes you want.

Investigations will usually include one or more of the following learning activities:

  • raising questions
  • planning
  • making observations
  • using practical skills
  • analysing data and looking for patterns
  • explaining and predicting.

Some investigations are relatively closed because there is an accepted view on what happens. Examples of this type of investigation include:

  • ‘Investigate the effect of temperature on the rate of reaction.’
  • ‘Investigating the relationship between the extension of a spring and the load (Hooke’s law).’
  • ‘Determine the value of g using the period of a pendulum.’

In these investigations, some students may already know the results they are aiming for, but they will still need to engage with many of the learning activities in the list above.

In order to learn how scientists work, students need the opportunity to investigate something where the answer is not known. For example, they could investigate which popular drink is the most acidic. In this case, they would have to think carefully about how to conduct a fair test, what measurements to make and how they would decide which was the most acidic.

You can also make investigations more open by asking your students to identify the factors they will investigate rather than telling them what factors to investigate. The more open an investigation is, the more students have to think about what will happen based on their understanding of the underlying science, and about what their results show in relation to these predictions. Open-ended investigations might have questions like: ‘What might be the best way to …?’ or ‘How can I find out what is the most likely cause of …?’

If your students are used to being told what to do, you cannot expect them to know how to plan an investigation. You will need to build their investigative skills by introducing more opportunities for discussing aspects such as choice of procedure, or what results they might expect and how they will analyse their results.

The activities in the textbook are usually structured practicals rather than investigations. However, you could adapt some of the activities to make them more like investigations and help your students develop investigative skills.

Case Study 2: Helping students to develop investigative skills

Mrs Bulsara discussed some strategies for developing investigative skills with colleagues at a local training session.

When I went to a training session last week, we discussed some things we might do during practical activities to help students to develop investigative skills.

The trainer gave each group of teachers two suggestions, and asked us to think how they might help our students. The two suggestions were as follows:

  1. When you are telling students about the practical activity they are going to do, ask them to predict what will happen and say why they think that.
  2. When students are working, ask them if their results are what they expected, and why.

We thought that asking for a prediction was helpful because it meant your students had to think about what they already know and relate it to this situation. If students make a prediction but can’t say why, then they haven’t understood something – so you need to help them.

We thought that the second suggestion was related to the first one, because you cannot be surprised by your results if you didn’t have some expectations of what they should be. If the result is something different from what you predicted, then you have to think what might be causing it. Maybe there was something odd with your procedure?

Next, we had to give two suggestions of our own. Here are our ideas:

  1. Before your students start any practical activity, ask them what they are going to measure or observe, why they are going to do that, and how they are going to do that. We thought this would be helpful because sometimes students just follow instructions step by step and don’t really think about the activity as a whole or why they are doing it in a particular way.
  2. When students are working, ask them if they have made enough measurements or observations yet. We thought this would be useful because students should have at least five measurements before they try to plot a graph of their results. Also, as they look at their results, they should be able to see if there is a trend emerging, or if some results look ‘odd’. This should mean they take some more measurements to check if the ‘odd’ reading was a mistake, or if there is something that is really happening that they need to look at more closely.

Pause for thought

What suggestion would you make?

Mrs Bulsara makes the point that you can help students develop investigative skills by thinking carefully about how to present the practical work that you would normally do, in a more thoughtful manner. In Activity 3 you will tackle a standard experiment in a more investigative way; in Case Study 3, Mr Raja sets his class an open-ended investigation and reflects on the results.

Activity 3: Adapting an activity

This activity will help you to develop your in-class practice in managing a student investigation.

In this activity you are going to start from the existing set of instructions and associated text for Activity 10.7 (Archimedes’ Principle) in the Class IX textbook. You will adapt the activity so that it is more investigative.

What is the purpose of doing this experiment? It is to help students to understand Archimedes’ Principle. The activity described here will still do this, but it will replace some instructions with questions, and try to extend your students’ thinking about thrust and pressure.

Write these instructions and questions on the blackboard:

  1. Take a piece of stone and tie it to one end of a rubber string or a spring balance. Hold the balance or the string so the stone is suspended. What is the reading on the balance or the length of the string?
  2. You are going to slowly dip the stone into a container of water. What do you think will happen to the reading on the balance or the length of the string? Why do you think this will happen?
  3. Dip the stone into the water and watch carefully what happens to the reading on the balance, or the length of the string. Record the new reading. Was it what you expected? What happens when the stone is fully immersed? How far as the level of the water risen? (This will tell you the volume of the stone.)
  4. Repeat the experiment for stones of different sizes. What is the connection between the volume of the stone and the change in the reading on the balance?
  5. Prediction with a reason: what would be the effect of lowering the stone into other liquids, such as oil or molasses?
  6. (Extension) Prediction and reason: suppose we placed the stone in a small dish, weighed the stone plus dish in and out of water, and then wrapped it tightly in foil or clay having the same mass as the dish before weighing it in and out of water. What would we observe?

Using different liquids should lead students to relate the change in extension (and hence apparent change in weight) to change in upthrust from different densities of liquid: the greater the density of the liquid, the more upthrust it provides when displaced.

The last point should allow students to find out that increasing the volume displaced (by putting the stone into a dish) increases the apparent weight loss. The upthrust is greater as more water is displaced.

Figure 1 When students are working in a group, it is a good idea to assign roles. In this picture the group leader is working out who will be the scribe, who will collect and set up the apparatus and who will conduct the experiment.

Case Study 3: An investigation in class

Mrs Bulsara runs an investigation with her students.

Having attended a training session at the DIET, I was very keen to let my students do a proper investigation. I decided to do the helicopter investigation (see Resource 5).

First of all I made a simple helicopter. I stood on a chair and dropped it vertically. I asked Raki to time how long it took to fall. I then asked my students how we could make it fall faster. Someone suggested making the ‘wings’ smaller. Then I attached a paper clip and dropped it again. I explained that I wanted each group to think of something about the helicopter that they could change and then to investigate the effect of that change on the time it took to fall.

They worked in groups of six. Some groups made the wings progressively smaller, some added paper clips and one group made helicopters out of different types of paper. They had to decide how to measure the time and how to record their results. I asked each group to write a question to summarise what they were trying to find out.

Junta’s group realised that it was difficult to measure the time accurately so they made sure the same person did it every time and they took three measurements for each drop so they could work out the average time.

They got lots of readings very quickly so they had plenty of time to think about how to present the results and how to explain their conclusion.

My students really enjoyed the lesson and everyone was involved. When I thought about it afterwards, I realised that they had done lots of things that real scientists do. They had thought of a question to investigate, they had worked out how to make it a fair test, they had done trial runs in order to work out how best to manage the timing, they had decided how to record their results and they had written a conclusion. In other words they had discovered something that they didn’t already know.

I told each group, ‘Prepare a poster to describe what you have done and present it to the rest of the class.’ Finally I asked them how confident they were about their conclusion, what they had found difficult and how they could have improved the reliability of their results.

1 What kind of practical work?

3 Evaluating the effectiveness of a practical activity