Squeezing it all in + pondering momentum ?

This week’s episode was a bumper edition, and we had to work hard to keep it down to just under 27 minutes. I really wanted to put in the Practicals In Memoriam (PIM) section and this led to cutting down the interview. Robin and I have talked a few times about the ideal length for the episodes, and hit on 20 minutes as short enough for a commute, and short enough to listen to a few on the bounce when you find the podcast.

As our production skills improve longer ones are easier to do and each podcast has been longer than the previous, but I think we will aim to keep them short. On reflection we felt that this Episode 5 was rather “busy” and maybe we should have kept back the PIM for another day. It deserved a whole podcast of its own maybe.  But when you are aiming to hit a deadline you have to make a decision and run with it. We were still tossing it back and forth on Wednesday night.

Pine nut shooters (straws)

In other news I asked Robin if he had any ideas for a class practical that could explore momentum. I wheel out the air track every year, but it is not very inspiring. He came up with pea shooters and impulse (Ft). I would really like to do something quantitative so my idea from this is you propel the pea (in my case pine nut) as hard as you can and see how far it goes as you reduce the length of the straw.  Assuming that the force is constant whilst the nut is in the straw, then the acceleration will be too and the time in the straw will be proportional to the square root of its length (suvat). The impulse is the change in momentum, so the velocity will also be proportional to the square root of the straws length and the distance the nut travels will be too. That’s my theory, but it seems over-complicated and could be done with suvat without any reference to impulse at all!  I am still humming and hahing about whether to use it.

An alternative would be Stuart’s practical, rolling balls down the slope in to cups. From suvat I can get the students to show that velocity is proportional to square root of the distance up the ruler. But where do I go from there? Pre-schoolers could tell you the cups will go further if the ball rolls faster. If I keep the velocity the same then heavier cups don’t go as far, but again, there is no obvious momentum related quantitative results I can gather. I did use Stuart’s experiment at Open Evening yesterday. IT worked well until the volunteers got excited about monkey-hunter!

I think I will be rolling out the air-track and doing the pea shooters qualitatively. ?