In my A level physics class i have decided to find the amount of force required to break a karate striking board and relate it to how much force is required to break a human rib and a jaw etc The striking board is basically a board that has been cut in half so there is a snapping line across it. but not with a straight cut. looking straight at its flat surface (where you would strike) the cut across the middle is straight. but looking at the side edge reveals that the cut is a wiggly jigsaw type of joint that makes it very hard to seperate from hitting the flat surface. however if you hold the bottom half steady and push on the side edge of the top half it will slide off. this sliding ability means that i can adjust the board to be joined at half a board only or any fraction. please ask me if this is unclear as it is very hard to explain normally one person would grip the bottom half at the bottom edge and another person would grip the top half at the top edge, so the snapping line runs horizontally. then it would be struck near the centre of the board and it would snap leaving 2 people with half a board each. I plan to swing an iron wrecking ball into it so this method didnt seem safe to my physics teacher. Instead i am having to clamp the bottom half into a workbench and swing the wrecking ball into the top half to snap it off. after the joint has 'unclicked' and the boards are seperated they can be slotted back together. my question is how will the force required to snap the top half off be different to having it clamped at both edges and something snapping through the middle? As i can not think of any safe way to recreate the board being held at 2 edges and the ball striking through the middle i am forced to clamp the bottom half and snap the top half off. so can my results of froce required for snapping off the top half reveal the force required to break through the middle? its a tricky question but im sure you guys can help me.