Boulder Drop
This activity involves a two-part process:

1. Get a piece of plywood or particle board that’s roughly 2-3 feet wide by about 4 feet long. The first step is to texture one side of the board. Have kids help you do this by gluing on rocks with a heavy duty adhesive like liquid nails. Use rocks that are roughly an inch thick and one or two inches in length – something resembling your average landscaping rocks. Glue them a few inches apart from one another in random patterns covering the entirety of one side of the board. If you’re really ambitious, you can spackle, texture and paint the board as well.

2. After the board has dried and solidified, gather some pebbles and small rounded rocks. Set your board up against something so that it’s leaning at roughly a 45 degree angle with the textured side facing up. Make sure it’s resting in a stable position and isn’t going to fall over to smash any little fingers or toes. You may need to position an adult to hold it.

Have kids take the smaller rock and drop them from the top of the board to see how they tumble, as if they were boulders tumbling down the side of a mountain. They’ll each take a unique path down the board, almost like a plinko game. You can have kids make guesses about where they think each rock will land by placing small paper cups near the bottom of the board, aiming to land the boulder in their cup. Experiment with the board at different angles to see if this has any effect on the way the rocks fall.