Although it is the new or unusual which is normally a stimulus to curiosity, more familiar objects may be ones which are more productive in encouraging children to express questions for investigation, perhaps because they are likely to already have queries in their minds which can be released by the invitation to express them.
Another way of stimulating questions without constant recourse to things which the children will not have seen before, is to draw attention to important aspects by putting things together with very different properties. For instance, when investigating bouncing balls, what do children think of how a ball of plasticene 'bounces.' Questioning why the plasticene becomes flattened gives an important clue to why balls bounce back.
Setting aside time for children to describe what they have done is an important part of science experiences which can be used to encourage questions and make it legitimate for children to express questions and admit that there are things they don't know but want to know. It is best for the questions to come from the children rather than the teacher. So instead of the teacher interrogating the children, they should be invited to respond to 'What do you still want to know about....?'
More generally, the simple request 'What questions would you like to ask about....' can be regularly extended, either orally in writing, on work cards or sheets. Resisting the temptation, as a teacher, to do all the question raising is also a simple but important guideline. Raising questions is something children must learn to do for themselves, and this won't be encouraged if all the questions they pursue are raised for them.
Ways to encourage questioning
Have things in the classroom which stimulate curiosity.
(Ideas from Taking the Plunge 1985, p51)
Helping children to identify more clearly what they want to know and phrasing questions which can be answered by their own Inquiry