1. Pressure is defined as force per unit area and can be calculated using the equation p=F/A. 2. Atmospheric pressure can be measured using a mercury barometer, where atmospheric pressure pushes mercury up the tube. Pressure decreases with increasing altitude. 3. Pressure increases with depth in liquids and depends on the density of the liquid. Higher density liquids exert greater pressure at the same depth. 4. Hydraulic systems use incompressible liquids to multiply force through differences in applied and reacted areas. A small force applied to a small area can produce a larger force from the same pressure over a larger area.