I was doing a design lab with a slinky today. Students have to come up with a research question related to a slinky spring.  always like the students to choose something different so as the lesson progresses it becomes harder and harder to get one that I accept. One group investigated the relationship between the frequency of the oscillation of a vertical slinky and the displacement of the end. I of course thought that the frequency would be constant but it turned out to be linearly related. The only explanation is that its something to do with the fact that the slinky is oscillating under its own mass so doesn't behave like a massless spring with a mass hanging on the end. I think I am going to have to try this one myself.

It reminds me of a recent discussion on the OCC about whether design experiments can encourage students to learn wrong physics. I think they simply enable student to see what the reality is like. All the experiments that we set up for them are incredibly contrived so that they show just the thing we want them to.