Explain the physics formulas: Combined Gas Law, Density, Pressure, and Hydrostatic Pressure.

Here are the explanations for the physics formulas shown in your notes:

1. The Combined Gas Law:

   $$\frac{P_1 V_1}{T_1} = \frac{P_2 V_2}{T_2}$$

   This formula relates the pressure ($P$), volume ($V$), and absolute temperature ($T$) of a fixed amount of gas. The subscripts 1 and 2 denote the initial and final states of the gas, respectively.

2. Density:

   $$\rho = \frac{m}{V}$$

   This formula defines density ($\rho$) as the mass ($m$) of a substance per unit volume ($V$).

3. Pressure:

   $$P = \frac{F}{A}$$

   This is the fundamental definition of pressure ($P$), which is the force ($F$) applied perpendicular to a surface divided by the area ($A$) over which the force is distributed.

4. Hydrostatic Pressure:

   $$P = \rho g h$$

   This formula calculates the hydrostatic pressure ($P$) at a certain depth within a fluid. Here, $\rho$ is the density of the fluid, $g$ is the acceleration due to gravity, and $h$ is the depth or height of the fluid column.