Another use for the film containers: Weighing things in space. They can't use a balance, so time vibrations. You tape the film container to a hacksaw blade, clamping the other end so the blade is horizontal. Some tissue in the bottom stops your weights rattling around and spoinling the calibration. Use 3, then 4, 5, up to 10 pennies to calibrate. You may need to do some trial and error here depending on your hacksaw blades, and remember to put some tough tape over the sharp edge. Once you've got your calibration curve you can weigh (sorry, find the mass of) small objects.

Moments with Y9 - started off at the classroom door, put the weakest kid in the class right at the edge of the door (furthest away from the hinge) pushing with one index finger. Strongest kid in the class on the other side of the door pushing with index finger about 2 inches in from the hinge. On go both push, weakest kid wins, so add another kid on the other side of the door.. and up to 4 kids on the strong side before our weak kid was even struggling.

Doing Space - orbits and satellites yesterday - had some fun. Tied some rope (30 foot length) around the waist of a Y10 , I held the other end. I was the earth, he was the satellite/incoming meteor, the rope was the pull of gravity. He had to try and run in a straight line past me. He tried... and the rope pulled him in a neat circle around me - nicely reinfored some points about orbits after we'd already done the swinging bucket of water over the head demo.