Pressure

Pressure is the force exerted by something pushing on a surface, spread out over the area of that surface. When you blow up a balloon, for example, the air molecules inside constantly bump into the rubber walls, and that collective pushing creates the pressure that keeps the balloon inflated. The more force pushing down on a smaller area, the greater the pressure, which is why a sharp needle can pierce skin more easily than a blunt object pushing with the same total force.