Pressure is the force per unit area that is applied perpendicular to the surface of an object. It is measured in units of Pascals (Pa), which is equivalent to one Newton of force per square meter of area. Pressure plays a significant role in Chemistry and Physics, where it can affect chemical reactions, fluid behavior, and thermodynamic phenomena. Atmospheric pressure is caused by the weight of air molecules pressing down on the Earth’s surface, and it decreases with elevation due to the decreasing density of the atmosphere. This is why high-altitude climbers may experience altitude sickness, and why pilots need to carefully monitor their aircraft’s internal cabin pressure. Furthermore, pressure differences can cause numerous phenomena, including wind, sound waves, and the flow of fluids such as blood through the circulatory system.