Pressure — Science definition

Defined in 2 courses:

Where it is taught

In use

Within a stationary liquid, pressure increases with depth because more fluid lies above.

Pressure & Buoyant Forces

Keep the amount of gas constant and you are left with three players to juggle: pressure (P), volume (V), and temperature (T).

The Gas Laws

Questions using pressure

Problem 1

For a fixed force, spreading it over a larger area makes pressure…
  1. larger
  2. smaller
  3. always zero
  4. independent of area
Answer and explanation

smaller

Pressure = force ÷ area.

Problem 2

A 200 N force is spread over 0.5 m². Find pressure and compare with the same force on 0.25 m². Explain the reasoning in your own words.
Answer and explanation

400 Pa initially; reducing the area by half doubles pressure to 800 Pa.

Pressure=force/area=200/0.5=400 Pa.

Halving area gives 200/0.25=800 Pa.

Response criteria

  • Use the stated conditions.
  • Show the evidence or calculation.
  • Explain the conclusion and any stated limitation.

Problem 3

Illustrative pistons share fluid pressure 2,000 Pa. Areas are 0.01 and 0.04 m². A floating object separately displaces water with weight 8 N. Calculate piston forces and explain why a force gain is not free energy. Identify the upward force in the floating model.
Answer and explanation

Using force = pressure × area, the piston forces are 20 N and 80 N. In an ideal hydraulic arrangement, the larger force acts through a smaller distance while displaced volumes balance, so energy is not created. The displaced-fluid model gives an 8 N buoyant force; floating equilibrium also requires the object’s weight to be balanced.

Using force = pressure × area, the piston forces are 20 N and 80 N. In an ideal hydraulic arrangement, the larger force acts through a smaller distance while displaced volumes balance, so energy is not created. The displaced-fluid model gives an 8 N buoyant force; floating equilibrium also requires the object’s weight to be balanced.

Response criteria

  • Use the supplied conditions and relevant evidence.
  • Explain the scientific mechanism or calculation.
  • State a meaningful limitation or testable next step.

Problem 4

Deeper fluid exerts greater pressure on an equal-area patchDeeper fluid exerts greater pressure on an equal-area patchStationary waterShallower patchDeeper patchEqual patch areasGreater depth gives greater pressure above the surface reference in this model.Fluid pressure pushes in all directions; only selected side patches are shown.
The selected equal-area side patches compare pressure effects at different depths in stationary water. The deeper patch experiences a greater pressure contribution relative to the surface reference. The arrows are comparative forces on equal-area patches, not a claim that pressure is itself a vector only pointing sideways. A full fluid model includes pushes in all directions and the pressure at the surface.
For this unit’s illustrated case, would a downward-only force drawing fully describe pressure on a submerged object? Explain what is missing.
Answer and explanation

No. Fluid pushes on all surfaces, including sides and top/bottom. Pressure varies with depth; comparing the complete surface forces is needed to explain net buoyancy.

Depth means vertical distance below the fluid surface. Pressure is force per area, and direction belongs to the force on each surface. A single selected arrow cannot represent every force acting on an immersed object.

No. Fluid pushes on all surfaces, including sides and top/bottom. Pressure varies with depth; comparing the complete surface forces is needed to explain net buoyancy.

Response criteria

  • Use the named labels, directions or supplied quantities accurately.
  • Connect the visual evidence to the scientific mechanism or calculation.
  • State the relevant model conditions or limitation.

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