Motivating students to perform an experiment in technological design contexts

In a teaching-learning sequence on the subject of energy we have tried technological design contexts to motivate students by using only context-based reasons to perform experiments on the subject of energy. We use these experiments to have the students reinvent practical laws of energy conservation from their data. We expected students to see the need for an experiment to test their designs but in our first try-out we encountered some problems with this, basically blocking the intended path to understanding energy conservation. In our second try-out we have improved the learning materials effectively hereby finding several contextual reasons for students to perform an experiment but also an unexpected reason for students not to perform an experiment.