Comprehensive set of 12 balls for classroom demonstrations. Contents: * 1 drilled aluminum ball, 25mm diameter * 1 drilled copper ball, 25mm diameter * 1 drilled steel ball, 25mm diameter * 1 drilled wood ball, 25mm diameter * 2 drilled brass balls, 25mm diameter * 2 solid steel balls (one plain and one with suspension lugs) * 1 brass ball with hook, 38mm diameter * 1 steel ball with hook, 38mm diameter * 1 copper ball with hook, 38mm diameter * 1 cork ball, 38mm All drilled balls feature 3mm countersunk holes so pendulum cord knots can be recessed. Packed in a plastic storage box.