Pressure & Fluids

Pressure

• Pressure = Force / Area.
• More force or less area → more pressure.
• Atmospheric pressure at sea level ≈ 101 kPa (1 atm).

Pressure in Fluids

• Pressure increases with depth.
• At greater depth, more fluid above pushes down.
• Pressure at depth: $P = P_0 + \rho g h$.

Buoyancy

• Objects float when their density is less than the fluid's.
• Buoyant force = weight of displaced fluid.
• A more dense fluid provides more buoyant force (e.g., saltwater vs. freshwater).

Pascal's Principle

• Pressure applied to an enclosed fluid is transmitted equally in all directions.
• Basis of hydraulic systems (small force on small piston → large force on large piston).

Atmospheric Pressure

• Decreases with altitude (less air above).
• Affects boiling point: lower pressure → lower boiling point.

Passage summary: Students measure pressure at various depths in a water tank.

Q: What is the relationship between depth and pressure?

A: Pressure increases linearly with depth — about 10 kPa per meter (which equals $\rho g \approx 1000 \times 9.8 \approx 10\ \text{kPa/m}$).

• Pressure = Force/Area; increases with depth in fluids.
• Buoyancy: objects float if less dense than the fluid.
• Atmospheric pressure decreases with altitude.
• Pascal's principle: pressure is transmitted equally in enclosed fluids.