Physics - Pressure

OCR A-Level Physics 2022

Created: November 09, 2020 | Read markdown | About these notes | View in context | Study these flashcards |

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Definition and units of pressure

What is the word formula for pressure?

pressure-word-formula
\[\text{pressure} = \frac{\text{force}}{\text{area}}\]

What are the units of pressure?

pressure-units

pascals, $\text{Pa}$

What is one Pascal equal to?

pascal-equivalent

$1Nm^{-2}$, one Newton per square metre.

What is atmospheric pressure approximately equal to?

atmospheric-pressure-value
\[1\times10^{5} Pa\]

What is the symbol formula for pressure?

pressure-symbol-formula
\[P = \frac{F}{A}\]

Pressure in a fluid

What is a fluid?

fluid-definition

A gas or a liquid.

What is the symbol formula for the pressure in a fluid?

fluid-pressure-symbol-formula
\[P = \rho h g\]

What is the word formula for the pressure in a fluid?

fluid-pressure-word-formula
\[\text{pressure} = \text{density} \times \text{height} \times \text{gravitational field strength}\]

Deriving fluid pressure from a cylinder

If you have a cylinder with cross-sectional surface area $A$ and height $h$, what is the formula for its volume?

cylinder-volume-formula
\[V = A \times h\]

If you have a cylinder with volume $V$ and density $\rho$, what is the formula for its mass?

cylinder-mass-formula
\[m = V\rho\]

If you have a cylinder with mass $m$, what is the formula for its weight?

cylinder-weight-formula
\[W = m \times g\]

If you have a cylinder with weight $w$ and cross-sectional surface area $A$, what is a formula for the pressure in the fluid?

cylinder-pressure-from-weight
\[P = \frac{w}{A}\]

What is the symbol formula for pressure in a fluid?

fluid-pressure-symbol-formula-recap
\[P = \rho h g\]

Why area drops out of fluid pressure

What seems “magic” about the formula for pressure in a fluid?

fluid-pressure-area-independence

The surface area does not matter.

Why does the surface area part of the pressure in a fluid equation disappear?

fluid-pressure-area-cancellation

Because the area component of volume cancels out:

\[\frac{\rho g h \text{\sout{A}}}{\text{\sout{A}}}\]

What is the word formula for pressure in a fluid?

fluid-pressure-word-formula-recap
\[\text{density} \times \text{height} \times \text{gravitational field strength}\]

What does $\rho$ represent in the pressure in a fluid equation?

rho-meaning-fluid-pressure

The density of the fluid.

What assumption are you making for the pressure in a fluid equation?

fluid-pressure-constant-density-assumption

That the density of the fluid stays constant.



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