Stubborn balloon

Balloons pop when they are put on one nail and do not pop when they are placed on a lots of nails. Nails are sharp because they have a point with very little surface area. One nail point has a lot less surface area than, ten or more nail points. To pop a balloon, a nail has to exert a lot of pressure on the balloon (p=F/A). Pressure = force / area, so the smaller the area, the more pressure is exerted by the same amount of force. On a board with nails, the force is distributed over those nail points, so the pressure is lower and the balloon doesn't pop as easily.

Pushing against many points spreads the force and reduces pressure. In this experiment a balloon pushed hard against a bed of nails doesn't pop, but when pushed gently against a single nail, the nail penetrates the skin of the balloon and it pops easily.