AP Physics 2 Fluids, Thermo, and Modern Physics Cheat Sheet

Key Facts

• Fluid pressure at depth is $P = P_0 + \rho g h$, where $P_0$ is surface pressure and $h$ is depth below the surface.
• Buoyant force equals the weight of displaced fluid, so $F_B = \rho_{\text{fluid}} g V_{\text{disp}}$.
• For ideal incompressible flow, the continuity equation is $A_1 v_1 = A_2 v_2$.
• Bernoulli’s equation for steady ideal flow is $P + \frac{1}{2}\rho v^2 + \rho g y = \text{constant}$ along a streamline.
• The first law of thermodynamics is $\Delta U = Q - W$, where $W$ is work done by the system.
• Thermal efficiency for a heat engine is $e = \frac{W}{Q_H} = 1 - \frac{Q_C}{Q_H}$, and the maximum Carnot efficiency is $e_C = 1 - \frac{T_C}{T_H}$ using kelvin temperatures.
• Photon energy is quantized by $E = hf = \frac{hc}{\lambda}$, where $h$ is Planck’s constant.
• Mass-energy equivalence is $E = mc^2$, and nuclear energy changes can be found from $\Delta E = \Delta m c^2$.

Vocabulary

Gauge pressure

Gauge pressure is the pressure above atmospheric pressure, often written as $P_g = \rho g h$ for a fluid at rest.

Buoyant force

Buoyant force is the upward force on an object in a fluid caused by pressure increasing with depth.

Ideal fluid

An ideal fluid is incompressible, nonviscous, and flows steadily without turbulence.

Entropy

Entropy is a measure of energy dispersal or microscopic disorder, and for a reversible process $\Delta S = \frac{Q_{\text{rev}}}{T}$.

Photon

A photon is a quantum of electromagnetic radiation with energy $E = hf$.

Binding energy

Binding energy is the energy required to separate a nucleus into its individual protons and neutrons.