Pressure and Pressure Differences in Fluid

• A fluid can be a liquid or a gas.
• In any fluid, the forces due to pressure act on a given surface at right angles (normal to) the surface.
• The equation used to calculate pressure is Pressure = Force/Area, where Pressure is in Pascals, Force is in Newtons, and Area is in metre².
• The density of the atmosphere decreases with increasing altitude.
• Atmospheric pressure decreases with an increase in height because pressure is created by collisions of air molecules, the quantity of molecules (and so weight) decreases as the height increases.
• The Earth’s atmosphere is a thin (relative to the magnitude of the Earth) layer of gas surrounding the Earth.
• In fluids, pressure increases with depth because as the depth increases, the mass of liquid above that depth also increases, meaning that the force due to the mass increases.
• An object with a density greater than that of water can never float because upthrust is equal to the weight of the displaced fluid.
• Upthrust is an upwards force that acts on an object when it is submerged in a fluid, equal to the weight of the fluid that the object displaces.
• Upthrust is always equal to the weight of the fluid that the object displaces.
• The force on a fluid has increased whilst the area has remained constant, resulting in an increase in pressure.
• The magnitude of pressure in liquids can be calculated using the equation P = hρg.
• The factors that influence whether an object will sink or float include upthrust, weight, and the density of the fluid.
• As the density of a fluid increases, the number of particles in a given volume increases, leading to a greater weight of the fluid and a larger force from the fluid above a certain point.