Here you have to block the matchstick inside the prongs of 2 intertwined forks. Place them carefully on the edge of the glass feeling for the point where the whole thing is balanced. With a bit of practice you can do it very quickly and always be very impressing!
Here I have represented the fulcrum point of the 2 forks by G1 and by G2. These being exactly the same, the fulcrum point of the whole is in the middle of G1G2 that is G. This point is precisely on the vertical from the point of contact P of the match on the glass. This last condition is necessary for the balance of the system. As G is situated lower than P so balance is stable that is you can move it a bit without it falling down...
