Question 1

Why does pressure increase with depth in a fluid?

Accepted Answer

At any depth, the fluid must support the weight of all the fluid above it. The greater the depth, the more fluid mass overhead, and therefore the greater the downward force per unit area (pressure). Mathematically, considering a thin horizontal slice of fluid at depth h, the pressure must equal the weight per unit area of the column above: P = ρgh. This is why the pressure at 10 m depth in water is approximately one additional atmosphere (101 kPa).

Question 2

How does a hydraulic press multiply force?

Accepted Answer

A hydraulic press has two pistons connected by an enclosed fluid. Pressing down on the small piston (area A₁) with force F₁ creates pressure P = F₁/A₁. Pascal's principle transmits this pressure undiminished to the large piston (area A₂), which experiences an upward force F₂ = P·A₂ = F₁·(A₂/A₁). If A₂ is 100 times A₁, the force is multiplied 100-fold. The small piston must move 100 times farther than the large piston, so no energy is created—work in equals work out (minus friction losses).

Question 3

What is gauge pressure versus absolute pressure?

Accepted Answer

Absolute pressure is total pressure measured relative to perfect vacuum. Gauge pressure is the pressure relative to local atmospheric pressure: P_gauge = P_absolute − P_atm. A tire inflated to 35 psi (gauge) actually contains air at about 50 psi absolute (35 + 14.7 atmospheric). Vacuum gauges read negative gauge pressure. Gauge pressure is more practically useful since instruments and systems typically interact with the local atmosphere as their reference, but absolute pressure is needed for thermodynamic calculations.

Question 4

Why do fluids exert pressure in all directions, not just downward?

Accepted Answer

Pressure in a fluid is isotropic because fluid molecules are in constant random thermal motion and strike surfaces from all angles with equal average momentum per unit area. If pressure were not isotropic, fluid elements would accelerate until equilibrium was restored. This isotropy is what makes hydraulic systems work—pushing on one side transmits pressure sideways and upward equally.

Question 5

How does Archimedes' principle relate to fluid pressure?

Accepted Answer

A submerged object experiences an upward buoyant force equal to the weight of fluid it displaces, because the bottom of the object sits at greater depth (higher pressure) than the top. The pressure difference integrated over the object's surface always equals rho_fluid * g * V_displaced, regardless of shape.

Question 6

What do the density presets (water, oil, seawater, mercury, ethanol) actually change?

Accepted Answer

Each preset sets rho directly (water 1000, oil 850, seawater 1025, mercury 13600, ethanol 789 kg/m3). Since P = P0 + rho*g*h, switching from water to mercury multiplies the hydrostatic term 13.6x — why mercury barometers need only ~76 cm to balance one atmosphere versus 10+ m for water.

Question 7

Why does moving the Column Height slider change pressure in a straight line rather than curving?

Accepted Answer

Hydrostatic pressure is computed as Ph = rho*g*colH, a direct linear multiplication. Doubling the column height doubles the added pressure because each metre of fluid overhead adds the same fixed weight per unit area, unlike atmospheric pressure which falls off exponentially in a compressible gas.

Question 8

How is the Hydraulic F2 readout calculated from Piston 1 and Piston 2 areas?

Accepted Answer

F2 is computed as F1*(A2/A1). With the default 10 cm2 small piston and 100 cm2 large piston the mechanical advantage is 10x, so a 100 N push yields 1000 N at the large piston; increasing A2 while A1 stays fixed increases this ratio directly.

Question 9

Is the acceleration due to gravity adjustable in this simulation?

Accepted Answer

No — g is fixed at 9.81 m/s2 throughout, since it appears in the hydrostatic and buoyancy formulas. Only fluid density, applied pressure, column height, and piston areas are exposed as sliders, keeping focus on how those four variables interact.

Question 10

How does the simulation compute the buoyant force Fb shown in the formula panel?

Accepted Answer

The panel shows Fb = rho*g*V using a fixed representative displaced volume of 0.1 m3, so the buoyancy formula can be read alongside the hydrostatic and hydraulic ones. Because rho is the same density slider used for the column, switching to mercury multiplies Fb by 13.6x, showing why identical objects feel more buoyant in denser fluids.

💧 Fluid Pressure — Pascal's Law & Hydrostatics

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