Welcome to my first toddler science post! I can't really take full credit for this as Squiblet gave me the idea when she found a cardboard tube. It was a great rainy day activity...if you don't mind messy windows!
We gathered a selection of tubes and watched the ball drop through them. We then taped the tubes to the window (we used fun red spotty tape as I happened to have some in the cupboard and it doesn't leave a residue like Sellotape on windows). We managed to make the ball run down the tube, along a piece of card and into the next tube. Squiblet thought it was hilarious when the ball fell out and enjoyed putting the ball in the top and sticking the tubes to the wall. Then she would try pulling them off and soon realised that the ball rolled out if she pointed it down.
All in all...cheap, jolly fun and she was learning about gravity, speed and forces without knowing it! Painless physics can only be a good plan in my book!