# Physics - Pressure

> Source: https://ollybritton.com/notes/a-level/physics/topics/pressure/ · Updated: 2020-11-09 · Tags: physics, pressure, year-1

See also:
- [Physics - Archimedes' Principle](https://ollybritton.com/notes/a-level/physics/topics/archimedes-principle/)

##### What is the word formula for pressure??
$$
\text{pressure} = \frac{\text{force}}{\text{area}}
$$

##### What are the units of pressure??
pascals, $\text{Pa}$

##### What is one Pascal equal to??
$1Nm^{-2}$, one Newton per square metre.

##### What is atmospheric pressure approximately equal to??
$$
1\times10^{5} Pa
$$

##### What is the symbol formula for pressure??
$$
P = \frac{F}{A}
$$

##### What is a fluid??
A gas or a liquid.

##### What is the symbol formula for the pressure in a fluid??
$$
P = \rho h g
$$

##### What is the word formula for the pressure in a fluid??
$$
\text{pressure} = \text{density} \times \text{height} \times \text{gravitational field strength}
$$

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

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

##### If you have a cyclinder with mass $m$, what is the formula for its weight??
$$
W = m \times g
$$

##### If you have a cylinder with weight $w$ and cross-sectional surface area $A$, what is a formula for the pressure in the fluid??
$$
P = \frac{w}{A}
$$

##### What is the symbol formula for pressure in a fluid??
$$
P = \rho h g
$$

##### What seems "magic" about the formula for pressure in a fluid??
The surface area does not matter.

##### Why does the surface area part of the pressure in a fluid equation dissapear??
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??
$$
\text{density} \times \text{height} \times \text{gravitational field strength}
$$

##### What does $\rho$ represent in the pressure in a fluid equation??
The density of the fluid.

##### What assumption are you making for the pressure in a fluid equation??
That the density of the fluid stays constant.

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