in activity you learned about center of gravity.
What is role of center of gravity with the nail balancer why don’t the overhanging nails tip the system over? Did you ever see a tightrope walker? They usually carry a low bending pole. Can you see a similarity with the nail balance? Do some research about tightrope walkers and learn What you can about the way they use center of gravity to their advantage.
Note:
Although nails are stretching out in two directions, the fourteen nails will balance one the first nail, because the centre of gravity is at the centre of system of nails. The overhanging nails actually hold the system in balance, instead of tipping it over as one might expect at first glance. Tightrope walkers use low bending poles to help them balance for the same reason.