Pressure exists on surfaces, in air and in liquids. On surfaces, pressure is calculated by dividing force by area. Atmospheric pressure decreases with height, and liquid pressure increases with depth. You should never swing on one leg of a chair. Not only can it break the chair, but it can also damage the floor. This is because you are applying too much pressure to the floor. To calculate pressure, you need to know two things: the force or weight exerted, and: the surface area over which the fo