1. Pressure

2. What is Pressure? Pressure refers to a force exerted on a surface Due to the force of gravity, your feet exert a force on the ground in the form of pressure Force and pressure are related, but they are not the same thing Pressure decreases as the area over which a force is distributed increases The larger the area over which the force is distributed, the less pressure is exerted

3. Fluid Pressure The SI unit of pressure is the pascal (Pa) A fluid is a material that can easily flow Particles in a fluid constantly move in all directions and collide with each other and any surface that they meet As the particles collide, they exert a force on the surface All of the forces exerted by the individual particles in a fluid combine to make up the pressure exerted by the fluid Air is a fluid that exerts pressure because it has mass The weight of the air is the force that produces air pressure Air pressure can be both balanced and unbalanced

4. Variations in Fluid Pressure Atmospheric Pressure and Elevation Water Pressure and Depth At higher elevations, there is less air above you, therefore less air pressure As elevation increases, atmospheric pressure decreases The “popping” of your ears as you go up a mountain, is your body’s way of balancing out the pressure inside your body to match the outside pressure Fluid pressure depends on depth Water pressure increases as depth increases The pressure in the water is not just due to the water itself, but it is also due to the air in the atmosphere pushing down on the water

5. Measuring Pressure A barometer is the instrument used to measure atmospheric pressure There are two types of barometers: a mercury barometer and an aneroid barometer Weather forecasters use the pressure reading from a barometer to help forecast weather Rapidly decreasing atmospheric pressure usually means a storm Increasing pressure is often a sign of fair weather